Merge pull request #2565 from cfallin/debug-value-labels

Detailed debug-info (DWARF) support in new backends (initially x64).

.github/workflows/main.yml

@@ -292,6 +292,14 @@ jobs:
       env:
         RUST_BACKTRACE: 1
 
+    # Test debug (DWARF) related functionality on new backend.
+    - run: |
+        sudo apt-get update && sudo apt-get install -y gdb
+        cargo test --features experimental_x64 test_debug_dwarf -- --ignored --test-threads 1 --test debug::
+      if: matrix.os == 'ubuntu-latest'
+      env:
+        RUST_BACKTRACE: 1
+
     # Build and test lightbeam. Note that
     # Lightbeam tests fail right now, but we don't want to block on that.
     - run: cargo build --package lightbeam

cranelift/codegen/Cargo.toml

@@ -74,7 +74,7 @@ all-arch = [
 ]
 
 # For dependent crates that want to serialize some parts of cranelift
-enable-serde = ["serde"]
+enable-serde = ["serde", "regalloc/enable-serde"]
 
 # Allow snapshotting regalloc test cases. Useful only to report bad register
 # allocation failures, or for regalloc.rs developers.

cranelift/codegen/src/context.rs

@@ -473,6 +473,7 @@ impl Context {
         Ok(build_value_labels_ranges::<ComparableSourceLoc>(
             &self.func,
             &self.regalloc,
+            self.mach_compile_result.as_ref(),
             isa,
         ))
     }

cranelift/codegen/src/ir/mod.rs

@@ -58,6 +58,7 @@ pub use crate::ir::table::TableData;
 pub use crate::ir::trapcode::TrapCode;
 pub use crate::ir::types::Type;
 pub use crate::ir::valueloc::{ArgumentLoc, ValueLoc};
+pub use crate::value_label::LabelValueLoc;
 pub use cranelift_codegen_shared::condcodes;
 
 use crate::binemit;

cranelift/codegen/src/isa/aarch64/inst/emit.rs

@@ -2371,6 +2371,9 @@ impl MachInstEmit for Inst {
                     sink.bind_label(jump_around_label);
                 }
             }
+            &Inst::ValueLabelMarker { .. } => {
+                // Nothing; this is only used to compute debug info.
+            }
         }
 
         let end_off = sink.cur_offset();

cranelift/codegen/src/isa/aarch64/inst/mod.rs

@@ -7,7 +7,7 @@ use crate::binemit::CodeOffset;
 use crate::ir::types::{
     B1, B128, B16, B32, B64, B8, F32, F64, FFLAGS, I128, I16, I32, I64, I8, I8X16, IFLAGS, R32, R64,
 };
-use crate::ir::{ExternalName, MemFlags, Opcode, SourceLoc, TrapCode, Type};
+use crate::ir::{ExternalName, MemFlags, Opcode, SourceLoc, TrapCode, Type, ValueLabel};
 use crate::isa::CallConv;
 use crate::machinst::*;
 use crate::{settings, CodegenError, CodegenResult};
@@ -1210,6 +1210,12 @@ pub enum Inst {
         /// The needed space before the next deadline.
         needed_space: CodeOffset,
     },
+
+    /// A definition of a value label.
+    ValueLabelMarker {
+        reg: Reg,
+        label: ValueLabel,
+    },
 }
 
 fn count_zero_half_words(mut value: u64, num_half_words: u8) -> usize {
@@ -2017,6 +2023,9 @@ fn aarch64_get_regs(inst: &Inst, collector: &mut RegUsageCollector) {
             memarg_regs(mem, collector);
         }
         &Inst::VirtualSPOffsetAdj { .. } => {}
+        &Inst::ValueLabelMarker { reg, .. } => {
+            collector.add_use(reg);
+        }
         &Inst::EmitIsland { .. } => {}
     }
 }
@@ -2767,6 +2776,9 @@ fn aarch64_map_regs<RUM: RegUsageMapper>(inst: &mut Inst, mapper: &RUM) {
         }
         &mut Inst::VirtualSPOffsetAdj { .. } => {}
         &mut Inst::EmitIsland { .. } => {}
+        &mut Inst::ValueLabelMarker { ref mut reg, .. } => {
+            map_use(mapper, reg);
+        }
     }
 }
 
@@ -2962,6 +2974,17 @@ impl MachInst for Inst {
     fn ref_type_regclass(_: &settings::Flags) -> RegClass {
         RegClass::I64
     }
+
+    fn gen_value_label_marker(label: ValueLabel, reg: Reg) -> Self {
+        Inst::ValueLabelMarker { label, reg }
+    }
+
+    fn defines_value_label(&self) -> Option<(ValueLabel, Reg)> {
+        match self {
+            Inst::ValueLabelMarker { label, reg } => Some((*label, *reg)),
+            _ => None,
+        }
+    }
 }
 
 //=============================================================================
@@ -4071,6 +4094,10 @@ impl Inst {
                 format!("virtual_sp_offset_adjust {}", offset)
             }
             &Inst::EmitIsland { needed_space } => format!("emit_island {}", needed_space),
+
+            &Inst::ValueLabelMarker { label, reg } => {
+                format!("value_label {:?}, {}", label, reg.show_rru(mb_rru))
+            }
         }
     }
 }

cranelift/codegen/src/isa/aarch64/mod.rs

@@ -79,6 +79,7 @@ impl MachBackend for AArch64Backend {
             frame_size,
             disasm,
             unwind_info,
+            value_labels_ranges: None,
         })
     }
 

cranelift/codegen/src/isa/arm32/mod.rs

@@ -74,6 +74,7 @@ impl MachBackend for Arm32Backend {
             frame_size,
             disasm,
             unwind_info: None,
+            value_labels_ranges: None,
         })
     }
 

cranelift/codegen/src/isa/mod.rs

@@ -325,6 +325,12 @@ pub trait TargetIsa: fmt::Display + Send + Sync {
         Err(RegisterMappingError::UnsupportedArchitecture)
     }
 
+    #[cfg(feature = "unwind")]
+    /// Map a regalloc::Reg to its corresponding DWARF register.
+    fn map_regalloc_reg_to_dwarf(&self, _: ::regalloc::Reg) -> Result<u16, RegisterMappingError> {
+        Err(RegisterMappingError::UnsupportedArchitecture)
+    }
+
     /// Returns an iterator over legal encodings for the instruction.
     fn legal_encodings<'a>(
         &'a self,

cranelift/codegen/src/isa/x64/inst/emit.rs

@@ -3029,6 +3029,10 @@ pub(crate) fn emit(
             sink.put1(0xff);
             sink.put1(0x17);
         }
+
+        Inst::ValueLabelMarker { .. } => {
+            // Nothing; this is only used to compute debug info.
+        }
     }
 
     state.clear_post_insn();

cranelift/codegen/src/isa/x64/inst/mod.rs

@@ -1,7 +1,7 @@
 //! This module defines x86_64-specific machine instruction types.
 
 use crate::binemit::{CodeOffset, StackMap};
-use crate::ir::{types, ExternalName, Opcode, SourceLoc, TrapCode, Type};
+use crate::ir::{types, ExternalName, Opcode, SourceLoc, TrapCode, Type, ValueLabel};
 use crate::isa::x64::abi::X64ABIMachineSpec;
 use crate::isa::x64::settings as x64_settings;
 use crate::isa::CallConv;
@@ -484,6 +484,9 @@ pub enum Inst {
     /// A Mach-O TLS symbol access. Returns address of the TLS
     /// symbol in rax.
     MachOTlsGetAddr { symbol: ExternalName },
+
+    /// A definition of a value label.
+    ValueLabelMarker { reg: Reg, label: ValueLabel },
 }
 
 pub(crate) fn low32_will_sign_extend_to_64(x: u64) -> bool {
@@ -544,7 +547,8 @@ impl Inst {
             | Inst::XmmMinMaxSeq { .. }
             | Inst::XmmUninitializedValue { .. }
             | Inst::ElfTlsGetAddr { .. }
-            | Inst::MachOTlsGetAddr { .. } => None,
+            | Inst::MachOTlsGetAddr { .. }
+            | Inst::ValueLabelMarker { .. } => None,
 
             // These use dynamic SSE opcodes.
             Inst::GprToXmm { op, .. }
@@ -1800,6 +1804,10 @@ impl PrettyPrint for Inst {
             Inst::MachOTlsGetAddr { ref symbol } => {
                 format!("macho_tls_get_addr {:?}", symbol)
             }
+
+            Inst::ValueLabelMarker { label, reg } => {
+                format!("value_label {:?}, {}", label, reg.show_rru(mb_rru))
+            }
         }
     }
 }
@@ -2071,6 +2079,10 @@ fn x64_get_regs(inst: &Inst, collector: &mut RegUsageCollector) {
                 collector.add_def(reg);
             }
         }
+
+        Inst::ValueLabelMarker { reg, .. } => {
+            collector.add_use(*reg);
+        }
     }
 }
 
@@ -2446,6 +2458,8 @@ fn x64_map_regs<RUM: RegUsageMapper>(inst: &mut Inst, mapper: &RUM) {
             dst.map_uses(mapper);
         }
 
+        Inst::ValueLabelMarker { ref mut reg, .. } => map_use(mapper, reg),
+
         Inst::Ret
         | Inst::EpiloguePlaceholder
         | Inst::JmpKnown { .. }
@@ -2536,6 +2550,25 @@ impl MachInst for Inst {
         }
     }
 
+    fn stack_op_info(&self) -> Option<MachInstStackOpInfo> {
+        match self {
+            Self::VirtualSPOffsetAdj { offset } => Some(MachInstStackOpInfo::NomSPAdj(*offset)),
+            Self::MovRM {
+                size: 8,
+                src,
+                dst: SyntheticAmode::NominalSPOffset { simm32 },
+            } => Some(MachInstStackOpInfo::StoreNomSPOff(*src, *simm32 as i64)),
+            Self::Mov64MR {
+                src: SyntheticAmode::NominalSPOffset { simm32 },
+                dst,
+            } => Some(MachInstStackOpInfo::LoadNomSPOff(
+                dst.to_reg(),
+                *simm32 as i64,
+            )),
+            _ => None,
+        }
+    }
+
     fn gen_move(dst_reg: Writable<Reg>, src_reg: Reg, ty: Type) -> Inst {
         let rc_dst = dst_reg.to_reg().get_class();
         let rc_src = src_reg.get_class();
@@ -2710,6 +2743,17 @@ impl MachInst for Inst {
         RegClass::I64
     }
 
+    fn gen_value_label_marker(label: ValueLabel, reg: Reg) -> Self {
+        Inst::ValueLabelMarker { label, reg }
+    }
+
+    fn defines_value_label(&self) -> Option<(ValueLabel, Reg)> {
+        match self {
+            Inst::ValueLabelMarker { label, reg } => Some((*label, *reg)),
+            _ => None,
+        }
+    }
+
     type LabelUse = LabelUse;
 }
 

cranelift/codegen/src/isa/x64/mod.rs

@@ -4,13 +4,14 @@ use self::inst::EmitInfo;
 
 use super::TargetIsa;
 use crate::ir::{condcodes::IntCC, Function};
+use crate::isa::unwind::systemv::RegisterMappingError;
 use crate::isa::x64::{inst::regs::create_reg_universe_systemv, settings as x64_settings};
 use crate::isa::Builder as IsaBuilder;
 use crate::machinst::{compile, MachBackend, MachCompileResult, TargetIsaAdapter, VCode};
 use crate::result::CodegenResult;
 use crate::settings::{self as shared_settings, Flags};
 use alloc::boxed::Box;
-use regalloc::{PrettyPrint, RealRegUniverse};
+use regalloc::{PrettyPrint, RealRegUniverse, Reg};
 use target_lexicon::Triple;
 
 mod abi;
@@ -60,6 +61,7 @@ impl MachBackend for X64Backend {
         let buffer = buffer.finish();
         let frame_size = vcode.frame_size();
         let unwind_info = vcode.unwind_info()?;
+        let value_labels_ranges = vcode.value_labels_ranges()?;
 
         let disasm = if want_disasm {
             Some(vcode.show_rru(Some(&create_reg_universe_systemv(flags))))
@@ -72,6 +74,7 @@ impl MachBackend for X64Backend {
             frame_size,
             disasm,
             unwind_info,
+            value_labels_ranges,
         })
     }
 
@@ -127,6 +130,11 @@ impl MachBackend for X64Backend {
     fn create_systemv_cie(&self) -> Option<gimli::write::CommonInformationEntry> {
         Some(inst::unwind::systemv::create_cie())
     }
+
+    #[cfg(feature = "unwind")]
+    fn map_reg_to_dwarf(&self, reg: Reg) -> Result<u16, RegisterMappingError> {
+        inst::unwind::systemv::map_reg(reg).map(|reg| reg.0)
+    }
 }
 
 /// Create a new `isa::Builder`.

cranelift/codegen/src/machinst/adapter.rs

@@ -10,6 +10,9 @@ use crate::settings::Flags;
 #[cfg(feature = "testing_hooks")]
 use crate::regalloc::RegDiversions;
 
+#[cfg(feature = "unwind")]
+use crate::isa::unwind::systemv::RegisterMappingError;
+
 use core::any::Any;
 use std::borrow::Cow;
 use std::fmt;
@@ -134,6 +137,11 @@ impl TargetIsa for TargetIsaAdapter {
         self.backend.create_systemv_cie()
     }
 
+    #[cfg(feature = "unwind")]
+    fn map_regalloc_reg_to_dwarf(&self, r: Reg) -> Result<u16, RegisterMappingError> {
+        self.backend.map_reg_to_dwarf(r)
+    }
+
     fn as_any(&self) -> &dyn Any {
         self as &dyn Any
     }

cranelift/codegen/src/machinst/debug.rs

@@ -0,0 +1,500 @@
+//! Debug info analysis: computes value-label ranges from value-label markers in
+//! generated VCode.
+//!
+//! We "reverse-engineer" debug info like this because it is far more reliable
+//! than generating it while emitting code and keeping it in sync.
+//!
+//! This works by (i) observing "value-label marker" instructions, which are
+//! semantically just an assignment from a register to a "value label" (which
+//! one can think of as another register; they represent, e.g., Wasm locals) at
+//! a certain point in the code, and (ii) observing loads and stores to the
+//! stack and register moves.
+//!
+//! We track, at every program point, the correspondence between each value
+//! label and *all* locations in which it resides. E.g., if it is stored to the
+//! stack, we remember that it is in both a register and the stack slot; but if
+//! the register is later overwritten, then we have it just in the stack slot.
+//! This allows us to avoid false-positives observing loads/stores that we think
+//! are spillslots but really aren't.
+//!
+//! We do a standard forward dataflow analysis to compute this info.
+
+use crate::ir::ValueLabel;
+use crate::machinst::*;
+use crate::value_label::{LabelValueLoc, ValueLabelsRanges, ValueLocRange};
+use log::trace;
+use regalloc::{Reg, RegUsageCollector};
+use std::collections::{HashMap, HashSet};
+use std::hash::Hash;
+
+/// Location of a labeled value: in a register or in a stack slot. Note that a
+/// value may live in more than one location; `AnalysisInfo` maps each
+/// value-label to multiple `ValueLoc`s.
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
+enum ValueLoc {
+    Reg(Reg),
+    /// Nominal-SP offset.
+    Stack(i64),
+}
+
+impl From<ValueLoc> for LabelValueLoc {
+    fn from(v: ValueLoc) -> Self {
+        match v {
+            ValueLoc::Reg(r) => LabelValueLoc::Reg(r),
+            ValueLoc::Stack(off) => LabelValueLoc::SPOffset(off),
+        }
+    }
+}
+
+impl ValueLoc {
+    fn is_reg(self) -> bool {
+        match self {
+            ValueLoc::Reg(_) => true,
+            _ => false,
+        }
+    }
+    fn is_stack(self) -> bool {
+        match self {
+            ValueLoc::Stack(_) => true,
+            _ => false,
+        }
+    }
+}
+
+/// Mappings at one program point.
+#[derive(Clone, Debug)]
+struct AnalysisInfo {
+    /// Nominal SP relative to real SP. If `None`, then the offset is
+    /// indeterminate (i.e., we merged to the lattice 'bottom' element). This
+    /// should not happen in well-formed code.
+    nominal_sp_offset: Option<i64>,
+    /// Forward map from labeled values to sets of locations.
+    label_to_locs: HashMap<ValueLabel, HashSet<ValueLoc>>,
+    /// Reverse map for each register indicating the value it holds, if any.
+    reg_to_label: HashMap<Reg, ValueLabel>,
+    /// Reverse map for each stack offset indicating the value it holds, if any.
+    stack_to_label: HashMap<i64, ValueLabel>,
+}
+
+/// Get the registers written (mod'd or def'd) by a machine instruction.
+fn get_inst_writes<M: MachInst>(m: &M) -> Vec<Reg> {
+    // TODO: expose this part of regalloc.rs's interface publicly.
+    let mut vecs = RegUsageCollector::get_empty_reg_vecs_test_framework_only(false);
+    let mut coll = RegUsageCollector::new(&mut vecs);
+    m.get_regs(&mut coll);
+    vecs.defs.extend(vecs.mods.into_iter());
+    vecs.defs
+}
+
+impl AnalysisInfo {
+    /// Create a new analysis state. This is the "top" lattice element at which
+    /// the fixpoint dataflow analysis starts.
+    fn new() -> Self {
+        AnalysisInfo {
+            nominal_sp_offset: Some(0),
+            label_to_locs: HashMap::new(),
+            reg_to_label: HashMap::new(),
+            stack_to_label: HashMap::new(),
+        }
+    }
+
+    /// Remove all locations for a given labeled value. Used when the labeled
+    /// value is redefined (so old values become stale).
+    fn clear_label(&mut self, label: ValueLabel) {
+        if let Some(locs) = self.label_to_locs.remove(&label) {
+            for loc in locs {
+                match loc {
+                    ValueLoc::Reg(r) => {
+                        self.reg_to_label.remove(&r);
+                    }
+                    ValueLoc::Stack(off) => {
+                        self.stack_to_label.remove(&off);
+                    }
+                }
+            }
+        }
+    }
+
+    /// Remove a label from a register, if any. Used, e.g., if the register is
+    /// overwritten.
+    fn clear_reg(&mut self, reg: Reg) {
+        if let Some(label) = self.reg_to_label.remove(&reg) {
+            if let Some(locs) = self.label_to_locs.get_mut(&label) {
+                locs.remove(&ValueLoc::Reg(reg));
+            }
+        }
+    }
+
+    /// Remove a label from a stack offset, if any. Used, e.g., when the stack
+    /// slot is overwritten.
+    fn clear_stack_off(&mut self, off: i64) {
+        if let Some(label) = self.stack_to_label.remove(&off) {
+            if let Some(locs) = self.label_to_locs.get_mut(&label) {
+                locs.remove(&ValueLoc::Stack(off));
+            }
+        }
+    }
+
+    /// Indicate that a labeled value is newly defined and its new value is in
+    /// `reg`.
+    fn def_label_at_reg(&mut self, label: ValueLabel, reg: Reg) {
+        self.clear_label(label);
+        self.label_to_locs
+            .entry(label)
+            .or_insert_with(|| HashSet::new())
+            .insert(ValueLoc::Reg(reg));
+        self.reg_to_label.insert(reg, label);
+    }
+
+    /// Process a store from a register to a stack slot (offset).
+    fn store_reg(&mut self, reg: Reg, off: i64) {
+        self.clear_stack_off(off);
+        if let Some(label) = self.reg_to_label.get(&reg) {
+            if let Some(locs) = self.label_to_locs.get_mut(label) {
+                locs.insert(ValueLoc::Stack(off));
+            }
+            self.stack_to_label.insert(off, *label);
+        }
+    }
+
+    /// Process a load from a stack slot (offset) to a register.
+    fn load_reg(&mut self, reg: Reg, off: i64) {
+        self.clear_reg(reg);
+        if let Some(&label) = self.stack_to_label.get(&off) {
+            if let Some(locs) = self.label_to_locs.get_mut(&label) {
+                locs.insert(ValueLoc::Reg(reg));
+            }
+            self.reg_to_label.insert(reg, label);
+        }
+    }
+
+    /// Process a move from one register to another.
+    fn move_reg(&mut self, to: Reg, from: Reg) {
+        self.clear_reg(to);
+        if let Some(&label) = self.reg_to_label.get(&from) {
+            if let Some(locs) = self.label_to_locs.get_mut(&label) {
+                locs.insert(ValueLoc::Reg(to));
+            }
+            self.reg_to_label.insert(to, label);
+        }
+    }
+
+    /// Update the analysis state w.r.t. an instruction's effects. Given the
+    /// state just before `inst`, this method updates `self` to be the state
+    /// just after `inst`.
+    fn step<M: MachInst>(&mut self, inst: &M) {
+        for write in get_inst_writes(inst) {
+            self.clear_reg(write);
+        }
+        if let Some((label, reg)) = inst.defines_value_label() {
+            self.def_label_at_reg(label, reg);
+        }
+        match inst.stack_op_info() {
+            Some(MachInstStackOpInfo::LoadNomSPOff(reg, offset)) => {
+                self.load_reg(reg, offset + self.nominal_sp_offset.unwrap());
+            }
+            Some(MachInstStackOpInfo::StoreNomSPOff(reg, offset)) => {
+                self.store_reg(reg, offset + self.nominal_sp_offset.unwrap());
+            }
+            Some(MachInstStackOpInfo::NomSPAdj(offset)) => {
+                if self.nominal_sp_offset.is_some() {
+                    self.nominal_sp_offset = Some(self.nominal_sp_offset.unwrap() + offset);
+                }
+            }
+            _ => {}
+        }
+        if let Some((to, from)) = inst.is_move() {
+            let to = to.to_reg();
+            self.move_reg(to, from);
+        }
+    }
+}
+
+/// Trait used to implement the dataflow analysis' meet (intersect) function
+/// onthe `AnalysisInfo` components. For efficiency, this is implemented as a
+/// mutation on the LHS, rather than a pure functional operation.
+trait IntersectFrom {
+    fn intersect_from(&mut self, other: &Self) -> IntersectResult;
+}
+
+/// Result of an intersection operation. Indicates whether the mutated LHS
+/// (which becomes the intersection result) differs from the original LHS. Also
+/// indicates if the value has become "empty" and should be removed from a
+/// parent container, if any.
+struct IntersectResult {
+    /// Did the intersection change the LHS input (the one that was mutated into
+    /// the result)? This is needed to drive the fixpoint loop; when no more
+    /// changes occur, then we have converted.
+    changed: bool,
+    /// Is the resulting value "empty"? This can be used when a container, such
+    /// as a map, holds values of this (intersection result) type; when
+    /// `is_empty` is true for the merge of the values at a particular key, we
+    /// can remove that key from the merged (intersected) result. This is not
+    /// necessary for analysis correctness but reduces the memory and runtime
+    /// cost of the fixpoint loop.
+    is_empty: bool,
+}
+
+impl IntersectFrom for AnalysisInfo {
+    fn intersect_from(&mut self, other: &Self) -> IntersectResult {
+        let mut changed = false;
+        changed |= self
+            .nominal_sp_offset
+            .intersect_from(&other.nominal_sp_offset)
+            .changed;
+        changed |= self
+            .label_to_locs
+            .intersect_from(&other.label_to_locs)
+            .changed;
+        changed |= self
+            .reg_to_label
+            .intersect_from(&other.reg_to_label)
+            .changed;
+        changed |= self
+            .stack_to_label
+            .intersect_from(&other.stack_to_label)
+            .changed;
+        IntersectResult {
+            changed,
+            is_empty: false,
+        }
+    }
+}
+
+impl<K, V> IntersectFrom for HashMap<K, V>
+where
+    K: Copy + Eq + Hash,
+    V: IntersectFrom,
+{
+    /// Intersection for hashmap: remove keys that are not in both inputs;
+    /// recursively intersect values for keys in common.
+    fn intersect_from(&mut self, other: &Self) -> IntersectResult {
+        let mut changed = false;
+        let mut remove_keys = vec![];
+        for k in self.keys() {
+            if !other.contains_key(k) {
+                remove_keys.push(*k);
+            }
+        }
+        for k in &remove_keys {
+            changed = true;
+            self.remove(k);
+        }
+
+        remove_keys.clear();
+        for k in other.keys() {
+            if let Some(v) = self.get_mut(k) {
+                let result = v.intersect_from(other.get(k).unwrap());
+                changed |= result.changed;
+                if result.is_empty {
+                    remove_keys.push(*k);
+                }
+            }
+        }
+        for k in &remove_keys {
+            changed = true;
+            self.remove(k);
+        }
+
+        IntersectResult {
+            changed,
+            is_empty: self.len() == 0,
+        }
+    }
+}
+impl<T> IntersectFrom for HashSet<T>
+where
+    T: Copy + Eq + Hash,
+{
+    /// Intersection for hashset: just take the set intersection.
+    fn intersect_from(&mut self, other: &Self) -> IntersectResult {
+        let mut changed = false;
+        let mut remove = vec![];
+        for val in self.iter() {
+            if !other.contains(val) {
+                remove.push(*val);
+            }
+        }
+        for val in remove {
+            changed = true;
+            self.remove(&val);
+        }
+
+        IntersectResult {
+            changed,
+            is_empty: self.len() == 0,
+        }
+    }
+}
+impl IntersectFrom for ValueLabel {
+    // Intersection for labeled value: remove if not equal. This is equivalent
+    // to a three-level lattice with top, bottom, and unordered set of
+    // individual labels in between.
+    fn intersect_from(&mut self, other: &Self) -> IntersectResult {
+        IntersectResult {
+            changed: false,
+            is_empty: *self != *other,
+        }
+    }
+}
+impl<T> IntersectFrom for Option<T>
+where
+    T: Copy + Eq,
+{
+    /// Intersectino for Option<T>: recursively intersect if both `Some`, else
+    /// `None`.
+    fn intersect_from(&mut self, other: &Self) -> IntersectResult {
+        let mut changed = false;
+        if !(self.is_some() && other.is_some() && self == other) {
+            changed = true;
+            *self = None;
+        }
+        IntersectResult {
+            changed,
+            is_empty: self.is_none(),
+        }
+    }
+}
+
+/// Compute the value-label ranges (locations for program-point ranges for
+/// labeled values) from a given `VCode` compilation result.
+///
+/// In order to compute this information, we perform a dataflow analysis on the
+/// machine code. To do so, and translate the results into a form usable by the
+/// debug-info consumers, we need to know two additional things:
+///
+/// - The machine-code layout (code offsets) of the instructions. DWARF is
+///   encoded in terms of instruction *ends* (and we reason about value
+///   locations at program points *after* instructions, to match this), so we
+///   take an array `inst_ends`, giving us code offsets for each instruction's
+///   end-point. (Note that this is one *past* the last byte; so a 4-byte
+///   instruction at offset 0 has an end offset of 4.)
+///
+/// - The locations of the labels to which branches will jump. Branches can tell
+///   us about their targets in terms of `MachLabel`s, but we don't know where
+///   those `MachLabel`s will be placed in the linear array of instructions.  We
+///   take the array `label_insn_index` to provide this info: for a label with
+///   index `l`, `label_insn_index[l]` is the index of the instruction before
+///   which that label is bound.
+pub(crate) fn compute<I: VCodeInst>(
+    insts: &[I],
+    inst_ends: &[u32],
+    label_insn_index: &[u32],
+) -> ValueLabelsRanges {
+    let inst_start = |idx: usize| if idx == 0 { 0 } else { inst_ends[idx - 1] };
+
+    trace!("compute: insts =");
+    for i in 0..insts.len() {
+        trace!(" #{} end: {} -> {:?}", i, inst_ends[i], insts[i]);
+    }
+    trace!("label_insn_index: {:?}", label_insn_index);
+
+    // Info at each block head, indexed by label.
+    let mut block_starts: HashMap<u32, AnalysisInfo> = HashMap::new();
+
+    // Initialize state at entry.
+    block_starts.insert(0, AnalysisInfo::new());
+
+    // Worklist: label indices for basic blocks.
+    let mut worklist = Vec::new();
+    let mut worklist_set = HashSet::new();
+    worklist.push(0);
+    worklist_set.insert(0);
+
+    while !worklist.is_empty() {
+        let block = worklist.pop().unwrap();
+        worklist_set.remove(&block);
+
+        let mut state = block_starts.get(&block).unwrap().clone();
+        trace!("at block {} -> state: {:?}", block, state);
+        // Iterate for each instruction in the block (we break at the first
+        // terminator we see).
+        let mut index = label_insn_index[block as usize];
+        while index < insts.len() as u32 {
+            state.step(&insts[index as usize]);
+            trace!(" -> inst #{}: {:?}", index, insts[index as usize]);
+            trace!("    --> state: {:?}", state);
+
+            let term = insts[index as usize].is_term();
+            if term.is_term() {
+                for succ in term.get_succs() {
+                    trace!("    SUCCESSOR block {}", succ.get());
+                    if let Some(succ_state) = block_starts.get_mut(&succ.get()) {
+                        trace!("       orig state: {:?}", succ_state);
+                        if succ_state.intersect_from(&state).changed {
+                            if worklist_set.insert(succ.get()) {
+                                worklist.push(succ.get());
+                            }
+                            trace!("        (changed)");
+                        }
+                        trace!("       new state: {:?}", succ_state);
+                    } else {
+                        // First time seeing this block
+                        block_starts.insert(succ.get(), state.clone());
+                        worklist.push(succ.get());
+                        worklist_set.insert(succ.get());
+                    }
+                }
+                break;
+            }
+
+            index += 1;
+        }
+    }
+
+    // Now iterate over blocks one last time, collecting
+    // value-label locations.
+
+    let mut value_labels_ranges: ValueLabelsRanges = HashMap::new();
+    for block in 0..label_insn_index.len() {
+        let start_index = label_insn_index[block];
+        let end_index = if block == label_insn_index.len() - 1 {
+            insts.len() as u32
+        } else {
+            label_insn_index[block + 1]
+        };
+        let block = block as u32;
+        let mut state = block_starts.get(&block).unwrap().clone();
+        for index in start_index..end_index {
+            let offset = inst_start(index as usize);
+            let end = inst_ends[index as usize];
+            state.step(&insts[index as usize]);
+
+            for (label, locs) in &state.label_to_locs {
+                trace!("   inst {} has label {:?} -> locs {:?}", index, label, locs);
+                // Find an appropriate loc: a register if possible, otherwise pick the first stack
+                // loc.
+                let reg = locs.iter().cloned().find(|l| l.is_reg());
+                let loc = reg.or_else(|| locs.iter().cloned().find(|l| l.is_stack()));
+                if let Some(loc) = loc {
+                    let loc = LabelValueLoc::from(loc);
+                    let list = value_labels_ranges.entry(*label).or_insert_with(|| vec![]);
+                    // If the existing location list for this value-label is
+                    // either empty, or has an end location that does not extend
+                    // to the current offset, then we have to append a new
+                    // entry. Otherwise, we can extend the current entry.
+                    //
+                    // Note that `end` is one past the end of the instruction;
+                    // it appears that `end` is exclusive, so a mapping valid at
+                    // offset 5 will have start = 5, end = 6.
+                    if list
+                        .last()
+                        .map(|last| last.end <= offset || last.loc != loc)
+                        .unwrap_or(true)
+                    {
+                        list.push(ValueLocRange {
+                            loc,
+                            start: end,
+                            end: end + 1,
+                        });
+                    } else {
+                        list.last_mut().unwrap().end = end + 1;
+                    }
+                }
+            }
+        }
+    }
+
+    trace!("ret: {:?}", value_labels_ranges);
+    value_labels_ranges
+}

cranelift/codegen/src/machinst/lower.rs

@@ -13,6 +13,7 @@ use crate::ir::instructions::BranchInfo;
 use crate::ir::{
     ArgumentPurpose, Block, Constant, ConstantData, ExternalName, Function, GlobalValueData, Inst,
     InstructionData, MemFlags, Opcode, Signature, SourceLoc, Type, Value, ValueDef,
+    ValueLabelAssignments, ValueLabelStart,
 };
 use crate::machinst::{
     writable_value_regs, ABICallee, BlockIndex, BlockLoweringOrder, LoweredBlock, MachLabel, VCode,
@@ -24,7 +25,7 @@ use alloc::vec::Vec;
 use core::convert::TryInto;
 use log::debug;
 use regalloc::{Reg, StackmapRequestInfo, Writable};
-use smallvec::SmallVec;
+use smallvec::{smallvec, SmallVec};
 use std::fmt::Debug;
 
 /// An "instruction color" partitions CLIF instructions by side-effecting ops.
@@ -492,6 +493,14 @@ impl<'func, I: VCodeInst> Lower<'func, I> {
     }
 
     fn gen_retval_setup(&mut self, gen_ret_inst: GenerateReturn) {
+        // Hack: to keep `vmctx` alive, if it exists, we emit a value label here
+        // for it if debug info is requested. This ensures that it exists either
+        // in a register or spillslot throughout the entire function body, and
+        // allows for a better debugging experience.
+        if let Some(vmctx_val) = self.f.special_param(ArgumentPurpose::VMContext) {
+            self.emit_value_label_marks_for_value(vmctx_val);
+        }
+
         let retval_regs = self.retval_regs.clone();
         for (i, regs) in retval_regs.into_iter().enumerate() {
             let regs = writable_value_regs(regs);
@@ -725,6 +734,9 @@ impl<'func, I: VCodeInst> Lower<'func, I> {
             if has_side_effect || value_needed {
                 debug!("lowering: inst {}: {:?}", inst, self.f.dfg[inst]);
                 backend.lower(self, inst)?;
+                // Emit value-label markers if needed, to later recover debug
+                // mappings.
+                self.emit_value_label_markers_for_inst(inst);
             }
             if data.opcode().is_return() {
                 // Return: handle specially, using ABI-appropriate sequence.
@@ -744,6 +756,80 @@ impl<'func, I: VCodeInst> Lower<'func, I> {
         Ok(())
     }
 
+    fn get_value_labels<'a>(&'a self, val: Value, depth: usize) -> Option<&'a [ValueLabelStart]> {
+        if let Some(ref values_labels) = self.f.dfg.values_labels {
+            debug!(
+                "get_value_labels: val {} -> {} -> {:?}",
+                val,
+                self.f.dfg.resolve_aliases(val),
+                values_labels.get(&self.f.dfg.resolve_aliases(val))
+            );
+            let val = self.f.dfg.resolve_aliases(val);
+            match values_labels.get(&val) {
+                Some(&ValueLabelAssignments::Starts(ref list)) => Some(&list[..]),
+                Some(&ValueLabelAssignments::Alias { value, .. }) if depth < 10 => {
+                    self.get_value_labels(value, depth + 1)
+                }
+                _ => None,
+            }
+        } else {
+            None
+        }
+    }
+
+    fn emit_value_label_marks_for_value(&mut self, val: Value) {
+        let mut markers: SmallVec<[I; 4]> = smallvec![];
+        let regs = self.value_regs[val];
+        if regs.len() > 1 {
+            return;
+        }
+        let reg = regs.only_reg().unwrap();
+
+        if let Some(label_starts) = self.get_value_labels(val, 0) {
+            let labels = label_starts
+                .iter()
+                .map(|&ValueLabelStart { label, .. }| label)
+                .collect::<FxHashSet<_>>();
+            for label in labels {
+                debug!(
+                    "value labeling: defines val {:?} -> reg {:?} -> label {:?}",
+                    val, reg, label,
+                );
+                markers.push(I::gen_value_label_marker(label, reg));
+            }
+        }
+        for marker in markers {
+            self.emit(marker);
+        }
+    }
+
+    fn emit_value_label_markers_for_inst(&mut self, inst: Inst) {
+        if self.f.dfg.values_labels.is_none() {
+            return;
+        }
+
+        debug!(
+            "value labeling: srcloc {}: inst {}",
+            self.srcloc(inst),
+            inst
+        );
+        for &val in self.f.dfg.inst_results(inst) {
+            self.emit_value_label_marks_for_value(val);
+        }
+    }
+
+    fn emit_value_label_markers_for_block_args(&mut self, block: Block) {
+        if self.f.dfg.values_labels.is_none() {
+            return;
+        }
+
+        debug!("value labeling: block {}", block);
+        for &arg in self.f.dfg.block_params(block) {
+            self.emit_value_label_marks_for_value(arg);
+        }
+        self.finish_ir_inst(SourceLoc::default());
+    }
+
     fn finish_ir_inst(&mut self, loc: SourceLoc) {
         // `bb_insts` is kept in reverse order, so emit the instructions in
         // reverse order.
@@ -885,6 +971,7 @@ impl<'func, I: VCodeInst> Lower<'func, I> {
             // Original block body.
             if let Some(bb) = lb.orig_block() {
                 self.lower_clif_block(backend, bb)?;
+                self.emit_value_label_markers_for_block_args(bb);
             }
             // In-edge phi moves.
             if let Some((pred, inst, succ)) = lb.in_edge() {

cranelift/codegen/src/machinst/mod.rs

@@ -52,45 +52,9 @@
 //!         |                        - all symbolic stack references to
 //!         |                          stackslots and spillslots are resolved
 //!         |                          to concrete FP-offset mem addresses.)
-//!         | [block/insn ordering]
 //!         |
-//!     VCode<arch_backend::Inst>   (machine instructions:
+//!         | [binary emission via MachBuffer
-//!         |                        - vcode.final_block_order is filled in.
+//!         |  with streaming branch resolution/simplification]
-//!         |                        - new insn sequence from regalloc is
-//!         |                          placed back into vcode and block
-//!         |                          boundaries are updated.)
-//!         | [redundant branch/block
-//!         |  removal]
-//!         |
-//!     VCode<arch_backend::Inst>   (machine instructions:
-//!         |                        - all blocks that were just an
-//!         |                          unconditional branch are removed.)
-//!         |
-//!         | [branch finalization
-//!         |  (fallthroughs)]
-//!         |
-//!     VCode<arch_backend::Inst>   (machine instructions:
-//!         |                        - all branches are in lowered one-
-//!         |                          target form, but targets are still
-//!         |                          block indices.)
-//!         |
-//!         | [branch finalization
-//!         |  (offsets)]
-//!         |
-//!     VCode<arch_backend::Inst>   (machine instructions:
-//!         |                        - all branch offsets from start of
-//!         |                          function are known, and all branches
-//!         |                          have resolved-offset targets.)
-//!         |
-//!         | [MemArg finalization]
-//!         |
-//!     VCode<arch_backend::Inst>   (machine instructions:
-//!         |                        - all MemArg references to the constant
-//!         |                          pool are replaced with offsets.
-//!         |                        - all constant-pool data is collected
-//!         |                          in the VCode.)
-//!         |
-//!         | [binary emission]
 //!         |
 //!     Vec<u8>                     (machine code!)
 //!
@@ -98,11 +62,11 @@
 
 use crate::binemit::{CodeInfo, CodeOffset, StackMap};
 use crate::ir::condcodes::IntCC;
-use crate::ir::{Function, SourceLoc, Type};
+use crate::ir::{Function, SourceLoc, Type, ValueLabel};
 use crate::isa::unwind::input as unwind_input;
 use crate::result::CodegenResult;
 use crate::settings::Flags;
-
+use crate::value_label::ValueLabelsRanges;
 use alloc::boxed::Box;
 use alloc::vec::Vec;
 use core::fmt::Debug;
@@ -111,10 +75,13 @@ use regalloc::RegUsageCollector;
 use regalloc::{
     RealReg, RealRegUniverse, Reg, RegClass, RegUsageMapper, SpillSlot, VirtualReg, Writable,
 };
-use smallvec::SmallVec;
+use smallvec::{smallvec, SmallVec};
 use std::string::String;
 use target_lexicon::Triple;
 
+#[cfg(feature = "unwind")]
+use crate::isa::unwind::systemv::RegisterMappingError;
+
 pub mod lower;
 pub use lower::*;
 pub mod vcode;
@@ -137,6 +104,7 @@ pub mod inst_common;
 pub use inst_common::*;
 pub mod valueregs;
 pub use valueregs::*;
+pub mod debug;
 
 /// A machine instruction.
 pub trait MachInst: Clone + Debug {
@@ -163,6 +131,11 @@ pub trait MachInst: Clone + Debug {
         true
     }
 
+    /// If this is a load or store to the stack, return that info.
+    fn stack_op_info(&self) -> Option<MachInstStackOpInfo> {
+        None
+    }
+
     /// Generate a move.
     fn gen_move(to_reg: Writable<Reg>, from_reg: Reg, ty: Type) -> Self;
 
@@ -223,6 +196,17 @@ pub trait MachInst: Clone + Debug {
     /// be dependent on compilation flags.
     fn ref_type_regclass(_flags: &Flags) -> RegClass;
 
+    /// Does this instruction define a ValueLabel? Returns the `Reg` whose value
+    /// becomes the new value of the `ValueLabel` after this instruction.
+    fn defines_value_label(&self) -> Option<(ValueLabel, Reg)> {
+        None
+    }
+
+    /// Create a marker instruction that defines a value label.
+    fn gen_value_label_marker(_label: ValueLabel, _reg: Reg) -> Self {
+        Self::gen_nop(0)
+    }
+
     /// A label-use kind: a type that describes the types of label references that
     /// can occur in an instruction.
     type LabelUse: MachInstLabelUse;
@@ -285,6 +269,35 @@ pub enum MachTerminator<'a> {
     Indirect(&'a [MachLabel]),
 }
 
+impl<'a> MachTerminator<'a> {
+    /// Get the successor labels named in a `MachTerminator`.
+    pub fn get_succs(&self) -> SmallVec<[MachLabel; 2]> {
+        let mut ret = smallvec![];
+        match self {
+            &MachTerminator::Uncond(l) => {
+                ret.push(l);
+            }
+            &MachTerminator::Cond(l1, l2) => {
+                ret.push(l1);
+                ret.push(l2);
+            }
+            &MachTerminator::Indirect(ls) => {
+                ret.extend(ls.iter().cloned());
+            }
+            _ => {}
+        }
+        ret
+    }
+
+    /// Is this a terminator?
+    pub fn is_term(&self) -> bool {
+        match self {
+            MachTerminator::None => false,
+            _ => true,
+        }
+    }
+}
+
 /// A trait describing the ability to encode a MachInst into binary machine code.
 pub trait MachInstEmit: MachInst {
     /// Persistent state carried across `emit` invocations.
@@ -330,6 +343,8 @@ pub struct MachCompileResult {
     pub disasm: Option<String>,
     /// Unwind info.
     pub unwind_info: Option<unwind_input::UnwindInfo<Reg>>,
+    /// Debug info: value labels to registers/stackslots at code offsets.
+    pub value_labels_ranges: Option<ValueLabelsRanges>,
 }
 
 impl MachCompileResult {
@@ -386,13 +401,17 @@ pub trait MachBackend {
         Ok(None)
     }
 
-    /// Machine-specific condcode info needed by TargetIsa.
     /// Creates a new System V Common Information Entry for the ISA.
     #[cfg(feature = "unwind")]
     fn create_systemv_cie(&self) -> Option<gimli::write::CommonInformationEntry> {
         // By default, an ISA cannot create a System V CIE
         None
     }
+    /// Maps a regalloc::Reg to a DWARF register number.
+    #[cfg(feature = "unwind")]
+    fn map_reg_to_dwarf(&self, _: Reg) -> Result<u16, RegisterMappingError> {
+        Err(RegisterMappingError::UnsupportedArchitecture)
+    }
 }
 
 /// Expected unwind info type.
@@ -431,3 +450,15 @@ pub trait UnwindInfoGenerator<I: MachInstEmit> {
         context: UnwindInfoContext<I>,
     ) -> CodegenResult<Option<unwind_input::UnwindInfo<Reg>>>;
 }
+
+/// Info about an operation that loads or stores from/to the stack.
+#[derive(Clone, Copy, Debug)]
+pub enum MachInstStackOpInfo {
+    /// Load from an offset from the nominal stack pointer into the given reg.
+    LoadNomSPOff(Reg, i64),
+    /// Store to an offset from the nominal stack pointer from the given reg.
+    StoreNomSPOff(Reg, i64),
+    /// Adjustment of nominal-SP up or down. This value is added to subsequent
+    /// offsets in loads/stores above to produce real-SP offsets.
+    NomSPAdj(i64),
+}

cranelift/codegen/src/machinst/vcode.rs

@@ -21,7 +21,6 @@ use crate::ir::{self, types, Constant, ConstantData, SourceLoc};
 use crate::machinst::*;
 use crate::settings;
 use crate::timing;
-
 use regalloc::Function as RegallocFunction;
 use regalloc::Set as RegallocSet;
 use regalloc::{
@@ -110,11 +109,19 @@ pub struct VCode<I: VCodeInst> {
     /// Ranges for prologue and epilogue instructions.
     prologue_epilogue_ranges: Option<(InsnRange, Box<[InsnRange]>)>,
 
-    /// Instruction end offsets
+    /// Do we generate debug info?
-    insts_layout: RefCell<(Vec<u32>, u32)>,
+    generate_debug_info: bool,
+
+    /// Instruction end offsets, instruction indices at each label, and total
+    /// buffer size.  Only present if `generate_debug_info` is set.
+    insts_layout: RefCell<(Vec<u32>, Vec<u32>, u32)>,
 
     /// Constants.
     constants: VCodeConstants,
+
+    /// Are any debug value-labels present? If not, we can skip the
+    /// post-emission analysis.
+    has_value_labels: bool,
 }
 
 /// A builder for a VCode function body. This builder is designed for the
@@ -157,7 +164,13 @@ impl<I: VCodeInst> VCodeBuilder<I> {
         constants: VCodeConstants,
     ) -> VCodeBuilder<I> {
         let reftype_class = I::ref_type_regclass(abi.flags());
-        let vcode = VCode::new(abi, emit_info, block_order, constants);
+        let vcode = VCode::new(
+            abi,
+            emit_info,
+            block_order,
+            constants,
+            /* generate_debug_info = */ true,
+        );
         let stack_map_info = StackmapRequestInfo {
             reftype_class,
             reftyped_vregs: vec![],
@@ -242,6 +255,9 @@ impl<I: VCodeInst> VCodeBuilder<I> {
                 }
             }
         }
+        if insn.defines_value_label().is_some() {
+            self.vcode.has_value_labels = true;
+        }
         self.vcode.insts.push(insn);
         self.vcode.srclocs.push(self.cur_srcloc);
         if is_safepoint {
@@ -296,6 +312,7 @@ impl<I: VCodeInst> VCode<I> {
         emit_info: I::Info,
         block_order: BlockLoweringOrder,
         constants: VCodeConstants,
+        generate_debug_info: bool,
     ) -> VCode<I> {
         VCode {
             liveins: abi.liveins(),
@@ -314,8 +331,10 @@ impl<I: VCodeInst> VCode<I> {
             safepoint_insns: vec![],
             safepoint_slots: vec![],
             prologue_epilogue_ranges: None,
-            insts_layout: RefCell::new((vec![], 0)),
+            generate_debug_info,
+            insts_layout: RefCell::new((vec![], vec![], 0)),
             constants,
+            has_value_labels: false,
         }
     }
 
@@ -484,7 +503,8 @@ impl<I: VCodeInst> VCode<I> {
         buffer.reserve_labels_for_blocks(self.num_blocks() as BlockIndex);
         buffer.reserve_labels_for_constants(&self.constants);
 
-        let mut insts_layout = vec![0; self.insts.len()];
+        let mut inst_ends = vec![0; self.insts.len()];
+        let mut label_insn_iix = vec![0; self.num_blocks()];
 
         let mut safepoint_idx = 0;
         let mut cur_srcloc = None;
@@ -500,6 +520,7 @@ impl<I: VCodeInst> VCode<I> {
 
             let (start, end) = self.block_ranges[block as usize];
             buffer.bind_label(MachLabel::from_block(block));
+            label_insn_iix[block as usize] = start;
             for iix in start..end {
                 let srcloc = self.srclocs[iix as usize];
                 if cur_srcloc != Some(srcloc) {
@@ -526,7 +547,19 @@ impl<I: VCodeInst> VCode<I> {
 
                 self.insts[iix as usize].emit(&mut buffer, &self.emit_info, &mut state);
 
-                insts_layout[iix as usize] = buffer.cur_offset();
+                if self.generate_debug_info {
+                    // Buffer truncation may have happened since last inst append; trim inst-end
+                    // layout info as appropriate.
+                    let l = &mut inst_ends[0..iix as usize];
+                    for end in l.iter_mut().rev() {
+                        if *end > buffer.cur_offset() {
+                            *end = buffer.cur_offset();
+                        } else {
+                            break;
+                        }
+                    }
+                    inst_ends[iix as usize] = buffer.cur_offset();
+                }
             }
 
             if cur_srcloc.is_some() {
@@ -553,7 +586,16 @@ impl<I: VCodeInst> VCode<I> {
             buffer.defer_constant(label, data.alignment(), data.as_slice(), u32::max_value());
         }
 
-        *self.insts_layout.borrow_mut() = (insts_layout, buffer.cur_offset());
+        if self.generate_debug_info {
+            for end in inst_ends.iter_mut().rev() {
+                if *end > buffer.cur_offset() {
+                    *end = buffer.cur_offset();
+                } else {
+                    break;
+                }
+            }
+            *self.insts_layout.borrow_mut() = (inst_ends, label_insn_iix, buffer.cur_offset());
+        }
 
         buffer
     }
@@ -567,13 +609,27 @@ impl<I: VCodeInst> VCode<I> {
         let context = UnwindInfoContext {
             insts: &self.insts,
             insts_layout: &layout.0,
-            len: layout.1,
+            len: layout.2,
             prologue: prologue.clone(),
             epilogues,
         };
         I::UnwindInfo::create_unwind_info(context)
     }
 
+    /// Generates value-label ranges.
+    pub fn value_labels_ranges(&self) -> crate::result::CodegenResult<Option<ValueLabelsRanges>> {
+        if !self.has_value_labels {
+            return Ok(None);
+        }
+
+        let layout = &self.insts_layout.borrow();
+        Ok(Some(debug::compute(
+            &self.insts,
+            &layout.0[..],
+            &layout.1[..],
+        )))
+    }
+
     /// Get the IR block for a BlockIndex, if one exists.
     pub fn bindex_to_bb(&self, block: BlockIndex) -> Option<ir::Block> {
         self.block_order.lowered_order()[block as usize].orig_block()

cranelift/codegen/src/value_label.rs

@@ -1,13 +1,16 @@
 use crate::ir::{Function, SourceLoc, Value, ValueLabel, ValueLabelAssignments, ValueLoc};
 use crate::isa::TargetIsa;
+use crate::machinst::MachCompileResult;
 use crate::regalloc::{Context, RegDiversions};
 use crate::HashMap;
 use alloc::collections::BTreeMap;
 use alloc::vec::Vec;
 use core::cmp::Ordering;
+use core::convert::From;
 use core::iter::Iterator;
 use core::ops::Bound::*;
 use core::ops::Deref;
+use regalloc::Reg;
 
 #[cfg(feature = "enable-serde")]
 use serde::{Deserialize, Serialize};
@@ -17,13 +20,31 @@ use serde::{Deserialize, Serialize};
 #[cfg_attr(feature = "enable-serde", derive(Serialize, Deserialize))]
 pub struct ValueLocRange {
     /// The ValueLoc containing a ValueLabel during this range.
-    pub loc: ValueLoc,
+    pub loc: LabelValueLoc,
     /// The start of the range. It is an offset in the generated code.
     pub start: u32,
     /// The end of the range. It is an offset in the generated code.
     pub end: u32,
 }
 
+/// The particular location for a value.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[cfg_attr(feature = "enable-serde", derive(Serialize, Deserialize))]
+pub enum LabelValueLoc {
+    /// Old-backend location: RegUnit, StackSlot, or Unassigned.
+    ValueLoc(ValueLoc),
+    /// New-backend Reg.
+    Reg(Reg),
+    /// New-backend offset from stack pointer.
+    SPOffset(i64),
+}
+
+impl From<ValueLoc> for LabelValueLoc {
+    fn from(v: ValueLoc) -> Self {
+        LabelValueLoc::ValueLoc(v)
+    }
+}
+
 /// Resulting map of Value labels and their ranges/locations.
 pub type ValueLabelsRanges = HashMap<ValueLabel, Vec<ValueLocRange>>;
 
@@ -86,14 +107,18 @@ where
 pub fn build_value_labels_ranges<T>(
     func: &Function,
     regalloc: &Context,
+    mach_compile_result: Option<&MachCompileResult>,
     isa: &dyn TargetIsa,
 ) -> ValueLabelsRanges
 where
     T: From<SourceLoc> + Deref<Target = SourceLoc> + Ord + Copy,
 {
-    // FIXME(#1523): New-style backend does not yet have debug info.
+    if mach_compile_result.is_some() && mach_compile_result.unwrap().value_labels_ranges.is_some() {
-    if isa.get_mach_backend().is_some() {
+        return mach_compile_result
-        return HashMap::new();
+            .unwrap()
+            .value_labels_ranges
+            .clone()
+            .unwrap();
     }
 
     let values_labels = build_value_labels_index::<T>(func);
@@ -113,7 +138,7 @@ where
             .entry(label)
             .or_insert_with(Vec::new)
             .push(ValueLocRange {
-                loc,
+                loc: loc.into(),
                 start: range.0,
                 end: range.1,
             });

cranelift/codegen/src/write.rs

@@ -11,7 +11,7 @@ use crate::ir::{
 };
 use crate::isa::{RegInfo, TargetIsa};
 use crate::packed_option::ReservedValue;
-use crate::value_label::ValueLabelsRanges;
+use crate::value_label::{LabelValueLoc, ValueLabelsRanges};
 use crate::HashSet;
 use alloc::string::String;
 use alloc::vec::Vec;
@@ -278,11 +278,13 @@ pub fn write_block_header(
     writeln!(w, "):")
 }
 
-fn write_valueloc(w: &mut dyn Write, loc: ValueLoc, regs: &RegInfo) -> fmt::Result {
+fn write_valueloc(w: &mut dyn Write, loc: LabelValueLoc, regs: &RegInfo) -> fmt::Result {
     match loc {
-        ValueLoc::Reg(r) => write!(w, "{}", regs.display_regunit(r)),
+        LabelValueLoc::ValueLoc(ValueLoc::Reg(r)) => write!(w, "{}", regs.display_regunit(r)),
-        ValueLoc::Stack(ss) => write!(w, "{}", ss),
+        LabelValueLoc::ValueLoc(ValueLoc::Stack(ss)) => write!(w, "{}", ss),
-        ValueLoc::Unassigned => write!(w, "?"),
+        LabelValueLoc::ValueLoc(ValueLoc::Unassigned) => write!(w, "?"),
+        LabelValueLoc::Reg(r) => write!(w, "{:?}", r),
+        LabelValueLoc::SPOffset(off) => write!(w, "[sp+{}]", off),
     }
 }
 

crates/debug/src/transform/expression.rs

@@ -7,7 +7,7 @@ use std::collections::{HashMap, HashSet};
 use std::hash::{Hash, Hasher};
 use std::rc::Rc;
 use wasmtime_environ::entity::EntityRef;
-use wasmtime_environ::ir::{StackSlots, ValueLabel, ValueLabelsRanges, ValueLoc};
+use wasmtime_environ::ir::{LabelValueLoc, StackSlots, ValueLabel, ValueLabelsRanges, ValueLoc};
 use wasmtime_environ::isa::TargetIsa;
 use wasmtime_environ::wasm::{get_vmctx_value_label, DefinedFuncIndex};
 use wasmtime_environ::ModuleMemoryOffset;
@@ -131,27 +131,24 @@ impl CompiledExpression {
 const X86_64_STACK_OFFSET: i64 = 16;
 
 fn translate_loc(
-    loc: ValueLoc,
+    loc: LabelValueLoc,
     frame_info: Option<&FunctionFrameInfo>,
     isa: &dyn TargetIsa,
     add_stack_value: bool,
 ) -> Result<Option<Vec<u8>>> {
     Ok(match loc {
-        ValueLoc::Reg(reg) if add_stack_value => {
+        LabelValueLoc::ValueLoc(ValueLoc::Reg(reg)) => {
             let machine_reg = isa.map_dwarf_register(reg)?;
             let mut writer = ExpressionWriter::new();
+            if add_stack_value {
                 writer.write_op_reg(machine_reg)?;
-            Some(writer.into_vec())
+            } else {
-        }
-        ValueLoc::Reg(reg) => {
-            assert!(!add_stack_value);
-            let machine_reg = isa.map_dwarf_register(reg)?;
-            let mut writer = ExpressionWriter::new();
                 writer.write_op_breg(machine_reg)?;
                 writer.write_sleb128(0)?;
+            }
             Some(writer.into_vec())
         }
-        ValueLoc::Stack(ss) => {
+        LabelValueLoc::ValueLoc(ValueLoc::Stack(ss)) => {
             if let Some(frame_info) = frame_info {
                 if let Some(ss_offset) = frame_info.stack_slots[ss].offset {
                     let mut writer = ExpressionWriter::new();
@@ -165,6 +162,27 @@ fn translate_loc(
             }
             None
         }
+        LabelValueLoc::Reg(r) => {
+            let machine_reg = isa.map_regalloc_reg_to_dwarf(r)?;
+            let mut writer = ExpressionWriter::new();
+            if add_stack_value {
+                writer.write_op_reg(machine_reg)?;
+            } else {
+                writer.write_op_breg(machine_reg)?;
+                writer.write_sleb128(0)?;
+            }
+            Some(writer.into_vec())
+        }
+        LabelValueLoc::SPOffset(off) => {
+            let mut writer = ExpressionWriter::new();
+            writer.write_op_breg(X86_64::RSP.0)?;
+            writer.write_sleb128(off)?;
+            if !add_stack_value {
+                writer.write_op(gimli::constants::DW_OP_deref)?;
+            }
+            return Ok(Some(writer.into_vec()));
+        }
+
         _ => None,
     })
 }
@@ -172,13 +190,13 @@ fn translate_loc(
 fn append_memory_deref(
     buf: &mut Vec<u8>,
     frame_info: &FunctionFrameInfo,
-    vmctx_loc: ValueLoc,
+    vmctx_loc: LabelValueLoc,
     isa: &dyn TargetIsa,
 ) -> Result<bool> {
     let mut writer = ExpressionWriter::new();
     // FIXME for imported memory
     match vmctx_loc {
-        ValueLoc::Reg(vmctx_reg) => {
+        LabelValueLoc::ValueLoc(ValueLoc::Reg(vmctx_reg)) => {
             let reg = isa.map_dwarf_register(vmctx_reg)? as u8;
             writer.write_u8(gimli::constants::DW_OP_breg0.0 + reg)?;
             let memory_offset = match frame_info.vmctx_memory_offset() {
@@ -189,7 +207,7 @@ fn append_memory_deref(
             };
             writer.write_sleb128(memory_offset)?;
         }
-        ValueLoc::Stack(ss) => {
+        LabelValueLoc::ValueLoc(ValueLoc::Stack(ss)) => {
             if let Some(ss_offset) = frame_info.stack_slots[ss].offset {
                 writer.write_op_breg(X86_64::RBP.0)?;
                 writer.write_sleb128(ss_offset as i64 + X86_64_STACK_OFFSET)?;
@@ -207,6 +225,31 @@ fn append_memory_deref(
                 return Ok(false);
             }
         }
+        LabelValueLoc::Reg(r) => {
+            let reg = isa.map_regalloc_reg_to_dwarf(r)?;
+            writer.write_op_breg(reg)?;
+            let memory_offset = match frame_info.vmctx_memory_offset() {
+                Some(offset) => offset,
+                None => {
+                    return Ok(false);
+                }
+            };
+            writer.write_sleb128(memory_offset)?;
+        }
+        LabelValueLoc::SPOffset(off) => {
+            writer.write_op_breg(X86_64::RSP.0)?;
+            writer.write_sleb128(off)?;
+            writer.write_op(gimli::constants::DW_OP_deref)?;
+            writer.write_op(gimli::constants::DW_OP_consts)?;
+            let memory_offset = match frame_info.vmctx_memory_offset() {
+                Some(offset) => offset,
+                None => {
+                    return Ok(false);
+                }
+            };
+            writer.write_sleb128(memory_offset)?;
+            writer.write_op(gimli::constants::DW_OP_plus)?;
+        }
         _ => {
             return Ok(false);
         }
@@ -468,7 +511,7 @@ where
                 let _ = code_chunk; // suppresses warning for final flush
             }
         };
-    };
+    }
     // Find all landing pads by scanning bytes, do not care about
     // false location at this moment.
     // Looks hacky but it is fast; does not need to be really exact.
@@ -653,7 +696,7 @@ struct CachedValueLabelRange {
     func_index: DefinedFuncIndex,
     start: usize,
     end: usize,
-    label_location: HashMap<ValueLabel, ValueLoc>,
+    label_location: HashMap<ValueLabel, LabelValueLoc>,
 }
 
 struct ValueLabelRangesBuilder<'a, 'b> {
@@ -1179,7 +1222,7 @@ mod tests {
     fn create_mock_value_ranges() -> (ValueLabelsRanges, (ValueLabel, ValueLabel, ValueLabel)) {
         use std::collections::HashMap;
         use wasmtime_environ::entity::EntityRef;
-        use wasmtime_environ::ir::{ValueLoc, ValueLocRange};
+        use wasmtime_environ::ir::{LabelValueLoc, ValueLoc, ValueLocRange};
         let mut value_ranges = HashMap::new();
         let value_0 = ValueLabel::new(0);
         let value_1 = ValueLabel::new(1);
@@ -1187,7 +1230,7 @@ mod tests {
         value_ranges.insert(
             value_0,
             vec![ValueLocRange {
-                loc: ValueLoc::Unassigned,
+                loc: LabelValueLoc::ValueLoc(ValueLoc::Unassigned),
                 start: 0,
                 end: 25,
             }],
@@ -1195,7 +1238,7 @@ mod tests {
         value_ranges.insert(
             value_1,
             vec![ValueLocRange {
-                loc: ValueLoc::Unassigned,
+                loc: LabelValueLoc::ValueLoc(ValueLoc::Unassigned),
                 start: 5,
                 end: 30,
             }],
@@ -1204,12 +1247,12 @@ mod tests {
             value_2,
             vec![
                 ValueLocRange {
-                    loc: ValueLoc::Unassigned,
+                    loc: LabelValueLoc::ValueLoc(ValueLoc::Unassigned),
                     start: 0,
                     end: 10,
                 },
                 ValueLocRange {
-                    loc: ValueLoc::Unassigned,
+                    loc: LabelValueLoc::ValueLoc(ValueLoc::Unassigned),
                     start: 20,
                     end: 30,
                 },

crates/environ/src/data_structures.rs

@@ -3,8 +3,8 @@
 pub mod ir {
     pub use cranelift_codegen::binemit::{Reloc, StackMap};
     pub use cranelift_codegen::ir::{
-        types, AbiParam, ArgumentPurpose, JumpTableOffsets, LibCall, Signature, SourceLoc,
+        types, AbiParam, ArgumentPurpose, JumpTableOffsets, LabelValueLoc, LibCall, Signature,
-        StackSlots, TrapCode, Type, ValueLabel, ValueLoc,
+        SourceLoc, StackSlots, TrapCode, Type, ValueLabel, ValueLoc,
     };
     pub use cranelift_codegen::{ValueLabelsRanges, ValueLocRange};
 }

tests/all/debug/lldb.rs

@@ -137,7 +137,11 @@ check: exited with status
 #[ignore]
 #[cfg(all(
     any(target_os = "linux", target_os = "macos"),
-    target_pointer_width = "64"
+    target_pointer_width = "64",
+    // Ignore test on new backend. The value this is looking for is
+    // not available at the point that the breakpoint is set when
+    // compiled by the new backend.
+    not(feature = "experimental_x64"),
 ))]
 pub fn test_debug_dwarf_ptr() -> Result<()> {
     let output = lldb_with_script(

tests/all/debug/translate.rs

@@ -114,7 +114,11 @@ check:        DW_AT_decl_line	(10)
 #[cfg(all(
     any(target_os = "linux", target_os = "macos"),
     target_arch = "x86_64",
-    target_pointer_width = "64"
+    target_pointer_width = "64",
+    // Ignore test on new backend. This is a specific test with hardcoded
+    // offsets and the new backend compiles the return basic-block at a different
+    // offset, causing mismatches.
+    not(feature = "experimental_x64"),
 ))]
 fn test_debug_dwarf5_translate_lines() -> Result<()> {
     check_line_program(