Cranelift: Deduplicate ABI signatures during lowering (#4829)

* Cranelift: Deduplicate ABI signatures during lowering This commit creates the `SigSet` type which interns and deduplicates the ABI signatures that we create from `ir::Signature`s. The ABI signatures are now referred to indirectly via a `Sig` (which is a `cranelift_entity` ID), and we pass around a `SigSet` to anything that needs to access the actual underlying `SigData` (which is what `ABISig` used to be). I had to change a couple methods to return a `SmallInstVec` instead of emitting directly to work around what would otherwise be shared and exclusive borrows of the lowering context overlapping. I don't expect any of these to heap allocate in practice. This does not remove the often-unnecessary allocations caused by `ensure_struct_return_ptr_is_returned`. That is left for follow up work. This also opens the door for further shuffling of signature data into more efficient representations in the future, now that we have `SigSet` to store it all in one place and it is threaded through all the code. We could potentially move each signature's parameter and return vectors into one big vector shared between all signatures, for example, which could cut down on allocations and shrink the size of `SigData` since those `SmallVec`s have pretty large inline capacity. Overall, this refactoring gives a 1-7% speedup for compilation on `pulldown-cmark`: ``` compilation :: cycles :: benchmarks/pulldown-cmark/benchmark.wasm Δ = 8754213.66 ± 7526266.23 (confidence = 99%) dedupe.so is 1.01x to 1.07x faster than main.so! [191003295 234620642.20 280597986] dedupe.so [197626699 243374855.86 321816763] main.so compilation :: cycles :: benchmarks/bz2/benchmark.wasm No difference in performance. [170406200 194299792.68 253001201] dedupe.so [172071888 193230743.11 223608329] main.so compilation :: cycles :: benchmarks/spidermonkey/benchmark.wasm No difference in performance. [3870997347 4437735062.59 5216007266] dedupe.so [4019924063 4424595349.24 4965088931] main.so ``` * Use full path instead of import to avoid warnings in some build configurations Warnings will then cause CI to fail. * Move `SigSet` into `VCode`
2022-08-31 13:39:32 -07:00
parent 62c5af68b5
commit f18a1f1488
15 changed files with 455 additions and 196 deletions
--- a/cranelift/codegen/src/machinst/abi.rs
+++ b/cranelift/codegen/src/machinst/abi.rs
@@ -102,6 +102,8 @@
 //! ABI. See each platform's `abi.rs` implementation for details.

 use crate::binemit::StackMap;
+use crate::entity::{PrimaryMap, SecondaryMap};
+use crate::fx::FxHashMap;
 use crate::ir::types::*;
 use crate::ir::{ArgumentExtension, ArgumentPurpose, DynamicStackSlot, Signature, StackSlot};
 use crate::isa::TargetIsa;
@@ -526,9 +528,14 @@ pub trait ABIMachineSpec {
 // A vector of `ABIArg`s with inline capacity, since they are typically small.
 pub type ABIArgVec = SmallVec<[ABIArg; 6]>;

+/// The id of an ABI signature within the `SigSet`.
+#[derive(Copy, Clone, PartialEq, Eq, Hash, PartialOrd, Ord)]
+pub struct Sig(u32);
+cranelift_entity::entity_impl!(Sig);
+
 /// ABI information shared between body (callee) and caller.
 #[derive(Clone)]
-pub struct ABISig {
+pub struct SigData {
    /// Argument locations (regs or stack slots). Stack offsets are relative to
    /// SP on entry to function.
    args: ABIArgVec,
@@ -545,11 +552,11 @@ pub struct ABISig {
    call_conv: isa::CallConv,
 }

-impl ABISig {
+impl SigData {
    pub fn from_func_sig<M: ABIMachineSpec>(
        sig: &ir::Signature,
        flags: &settings::Flags,
-    ) -> CodegenResult<ABISig> {
+    ) -> CodegenResult<SigData> {
        let sig = ensure_struct_return_ptr_is_returned(sig);

        // Compute args and retvals from signature. Handle retvals first,
@@ -580,7 +587,7 @@ impl ABISig {
            stack_ret_arg,
        );

-        Ok(ABISig {
+        Ok(SigData {
            args,
            rets,
            sized_stack_arg_space,
@@ -698,12 +705,138 @@ impl ABISig {
    }
 }

+/// A (mostly) deduplicated set of ABI signatures.
+///
+/// We say "mostly" because we do not dedupe between signatures interned via
+/// `ir::SigRef` (direct and indirect calls; the vast majority of signatures in
+/// this set) vs via `ir::Signature` (the callee itself and libcalls). Doing
+/// this final bit of deduplication would require filling out the
+/// `ir_signature_to_abi_sig`, which is a bunch of allocations (not just the
+/// hash map itself but params and returns vecs in each signature) that we want
+/// to avoid.
+///
+/// In general, prefer using the `ir::SigRef`-taking methods to the
+/// `ir::Signature`-taking methods when you can get away with it, as they don't
+/// require cloning non-copy types that will trigger heap allocations.
+///
+/// This type can be indexed by `Sig` to access its associated `SigData`.
+pub struct SigSet {
+    /// Interned `ir::Signature`s that we already have an ABI signature for.
+    ir_signature_to_abi_sig: FxHashMap<ir::Signature, Sig>,
+
+    /// Interned `ir::SigRef`s that we already have an ABI signature for.
+    ir_sig_ref_to_abi_sig: SecondaryMap<ir::SigRef, Option<Sig>>,
+
+    /// The actual ABI signatures, keyed by `Sig`.
+    sigs: PrimaryMap<Sig, SigData>,
+}
+
+impl SigSet {
+    /// Construct a new `SigSet`, interning all of the signatures used by the
+    /// given function.
+    pub fn new<M>(func: &ir::Function, flags: &settings::Flags) -> CodegenResult<Self>
+    where
+        M: ABIMachineSpec,
+    {
+        let mut sigs = SigSet {
+            ir_signature_to_abi_sig: FxHashMap::default(),
+            ir_sig_ref_to_abi_sig: SecondaryMap::with_capacity(func.dfg.signatures.len()),
+            sigs: PrimaryMap::with_capacity(1 + func.dfg.signatures.len()),
+        };
+
+        sigs.make_abi_sig_from_ir_signature::<M>(func.signature.clone(), flags)?;
+        for sig_ref in func.dfg.signatures.keys() {
+            sigs.make_abi_sig_from_ir_sig_ref::<M>(sig_ref, &func.dfg, flags)?;
+        }
+
+        Ok(sigs)
+    }
+
+    /// Have we already interned an ABI signature for the given `ir::Signature`?
+    pub fn have_abi_sig_for_signature(&self, signature: &ir::Signature) -> bool {
+        self.ir_signature_to_abi_sig.contains_key(signature)
+    }
+
+    /// Construct and intern an ABI signature for the given `ir::Signature`.
+    pub fn make_abi_sig_from_ir_signature<M>(
+        &mut self,
+        signature: ir::Signature,
+        flags: &settings::Flags,
+    ) -> CodegenResult<Sig>
+    where
+        M: ABIMachineSpec,
+    {
+        // Because the `HashMap` entry API requires taking ownership of the
+        // lookup key -- and we want to avoid unnecessary clones of
+        // `ir::Signature`s, even at the cost of duplicate lookups -- we can't
+        // have a single, get-or-create-style method for interning
+        // `ir::Signature`s into ABI signatures. So at least (debug) assert that
+        // we aren't creating duplicate ABI signatures for the same
+        // `ir::Signature`.
+        debug_assert!(!self.have_abi_sig_for_signature(&signature));
+
+        let legalized_signature = crate::machinst::ensure_struct_return_ptr_is_returned(&signature);
+        let sig_data = SigData::from_func_sig::<M>(&legalized_signature, flags)?;
+        let sig = self.sigs.push(sig_data);
+        self.ir_signature_to_abi_sig.insert(signature, sig);
+        Ok(sig)
+    }
+
+    fn make_abi_sig_from_ir_sig_ref<M>(
+        &mut self,
+        sig_ref: ir::SigRef,
+        dfg: &ir::DataFlowGraph,
+        flags: &settings::Flags,
+    ) -> CodegenResult<Sig>
+    where
+        M: ABIMachineSpec,
+    {
+        if let Some(sig) = self.ir_sig_ref_to_abi_sig[sig_ref] {
+            return Ok(sig);
+        }
+        let signature = &dfg.signatures[sig_ref];
+        let legalized_signature = crate::machinst::ensure_struct_return_ptr_is_returned(&signature);
+        let sig_data = SigData::from_func_sig::<M>(&legalized_signature, flags)?;
+        let sig = self.sigs.push(sig_data);
+        self.ir_sig_ref_to_abi_sig[sig_ref] = Some(sig);
+        Ok(sig)
+    }
+
+    /// Get the already-interned ABI signature id for the given `ir::SigRef`.
+    pub fn abi_sig_for_sig_ref(&self, sig_ref: ir::SigRef) -> Sig {
+        self.ir_sig_ref_to_abi_sig
+            .get(sig_ref)
+            // Should have a secondary map entry...
+            .expect("must call `make_abi_sig_from_ir_sig_ref` before `get_abi_sig_for_sig_ref`")
+            // ...and that entry should be initialized.
+            .expect("must call `make_abi_sig_from_ir_sig_ref` before `get_abi_sig_for_sig_ref`")
+    }
+
+    /// Get the already-interned ABI signature id for the given `ir::Signature`.
+    pub fn abi_sig_for_signature(&self, signature: &ir::Signature) -> Sig {
+        self.ir_signature_to_abi_sig
+            .get(signature)
+            .copied()
+            .expect("must call `make_abi_sig_from_ir_signature` before `get_abi_sig_for_signature`")
+    }
+}
+
+// NB: we do _not_ implement `IndexMut` because these signatures are
+// deduplicated and shared!
+impl std::ops::Index<Sig> for SigSet {
+    type Output = SigData;
+
+    fn index(&self, sig: Sig) -> &Self::Output {
+        &self.sigs[sig]
+    }
+}
+
 /// ABI object for a function body.
 pub struct Callee<M: ABIMachineSpec> {
    /// CLIF-level signature, possibly normalized.
    ir_sig: ir::Signature,
    /// Signature: arg and retval regs.
-    sig: ABISig,
+    sig: Sig,
    /// Defined dynamic types.
    dynamic_type_sizes: HashMap<Type, u32>,
    /// Offsets to each dynamic stackslot.
@@ -761,7 +894,7 @@ pub struct Callee<M: ABIMachineSpec> {

 fn get_special_purpose_param_register(
    f: &ir::Function,
-    abi: &ABISig,
+    abi: &SigData,
    purpose: ir::ArgumentPurpose,
 ) -> Option<Reg> {
    let idx = f.signature.special_param_index(purpose)?;
@@ -776,12 +909,16 @@ fn get_special_purpose_param_register(

 impl<M: ABIMachineSpec> Callee<M> {
    /// Create a new body ABI instance.
-    pub fn new(f: &ir::Function, isa: &dyn TargetIsa, isa_flags: &M::F) -> CodegenResult<Self> {
+    pub fn new<'a>(
+        f: &ir::Function,
+        isa: &dyn TargetIsa,
+        isa_flags: &M::F,
+        sigs: &SigSet,
+    ) -> CodegenResult<Self> {
        trace!("ABI: func signature {:?}", f.signature);

        let flags = isa.flags().clone();
-        let ir_sig = ensure_struct_return_ptr_is_returned(&f.signature);
-        let sig = ABISig::from_func_sig::<M>(&ir_sig, &flags)?;
+        let sig = sigs.abi_sig_for_signature(&f.signature);

        let call_conv = f.signature.call_conv;
        // Only these calling conventions are supported.
@@ -839,9 +976,12 @@ impl<M: ABIMachineSpec> Callee<M> {
        // argument or as a global value which often calculates the stack limit
        // from the arguments.
        let stack_limit =
-            get_special_purpose_param_register(f, &sig, ir::ArgumentPurpose::StackLimit)
+            get_special_purpose_param_register(f, &sigs[sig], ir::ArgumentPurpose::StackLimit)
                .map(|reg| (reg, smallvec![]))
-                .or_else(|| f.stack_limit.map(|gv| gen_stack_limit::<M>(f, &sig, gv)));
+                .or_else(|| {
+                    f.stack_limit
+                        .map(|gv| gen_stack_limit::<M>(f, &sigs[sig], gv))
+                });

        // Determine whether a probestack call is required for large enough
        // frames (and the minimum frame size if so).
@@ -856,7 +996,7 @@ impl<M: ABIMachineSpec> Callee<M> {
        };

        Ok(Self {
-            ir_sig,
+            ir_sig: ensure_struct_return_ptr_is_returned(&f.signature),
            sig,
            dynamic_stackslots,
            dynamic_type_sizes,
@@ -959,7 +1099,7 @@ impl<M: ABIMachineSpec> Callee<M> {
 /// it's used, because we're not participating in register allocation anyway!
 fn gen_stack_limit<M: ABIMachineSpec>(
    f: &ir::Function,
-    abi: &ABISig,
+    abi: &SigData,
    gv: ir::GlobalValue,
 ) -> (Reg, SmallInstVec<M::I>) {
    let mut insts = smallvec![];
@@ -969,7 +1109,7 @@ fn gen_stack_limit<M: ABIMachineSpec>(

 fn generate_gv<M: ABIMachineSpec>(
    f: &ir::Function,
-    abi: &ABISig,
+    abi: &SigData,
    gv: ir::GlobalValue,
    insts: &mut SmallInstVec<M::I>,
 ) -> Reg {
@@ -1033,7 +1173,7 @@ fn gen_store_stack_multi<M: ABIMachineSpec>(
    ret
 }

-fn ensure_struct_return_ptr_is_returned(sig: &ir::Signature) -> ir::Signature {
+pub(crate) fn ensure_struct_return_ptr_is_returned(sig: &ir::Signature) -> ir::Signature {
    let params_structret = sig
        .params
        .iter()
@@ -1061,9 +1201,9 @@ impl<M: ABIMachineSpec> Callee<M> {

    /// Does the ABI-body code need temp registers (and if so, of what type)?
    /// They will be provided to `init()` as the `temps` arg if so.
-    pub fn temps_needed(&self) -> Vec<Type> {
+    pub fn temps_needed(&self, sigs: &SigSet) -> Vec<Type> {
        let mut temp_tys = vec![];
-        for arg in &self.sig.args {
+        for arg in &sigs[self.sig].args {
            match arg {
                &ABIArg::ImplicitPtrArg { pointer, .. } => match &pointer {
                    &ABIArgSlot::Reg { .. } => {}
@@ -1074,7 +1214,7 @@ impl<M: ABIMachineSpec> Callee<M> {
                _ => {}
            }
        }
-        if self.sig.stack_ret_arg.is_some() {
+        if sigs[self.sig].stack_ret_arg.is_some() {
            temp_tys.push(M::word_type());
        }
        temp_tys
@@ -1083,9 +1223,9 @@ impl<M: ABIMachineSpec> Callee<M> {
    /// Initialize. This is called after the Callee is constructed because it
    /// may be provided with a vector of temp vregs, which can only be allocated
    /// once the lowering context exists.
-    pub fn init(&mut self, temps: Vec<Writable<Reg>>) {
+    pub fn init(&mut self, sigs: &SigSet, temps: Vec<Writable<Reg>>) {
        let mut temps_iter = temps.into_iter();
-        for arg in &self.sig.args {
+        for arg in &sigs[self.sig].args {
            let temp = match arg {
                &ABIArg::ImplicitPtrArg { pointer, .. } => match &pointer {
                    &ABIArgSlot::Reg { .. } => None,
@@ -1095,7 +1235,7 @@ impl<M: ABIMachineSpec> Callee<M> {
            };
            self.arg_temp_reg.push(temp);
        }
-        if self.sig.stack_ret_arg.is_some() {
+        if sigs[self.sig].stack_ret_arg.is_some() {
            self.ret_area_ptr = Some(temps_iter.next().unwrap());
        }
    }
@@ -1113,8 +1253,8 @@ impl<M: ABIMachineSpec> Callee<M> {
    }

    /// Get the calling convention implemented by this ABI object.
-    pub fn call_conv(&self) -> isa::CallConv {
-        self.sig.call_conv
+    pub fn call_conv(&self, sigs: &SigSet) -> isa::CallConv {
+        sigs[self.sig].call_conv
    }

    /// The offsets of all sized stack slots (not spill slots) for debuginfo purposes.
@@ -1131,6 +1271,7 @@ impl<M: ABIMachineSpec> Callee<M> {
    /// register.
    pub fn gen_copy_arg_to_regs(
        &self,
+        sigs: &SigSet,
        idx: usize,
        into_regs: ValueRegs<Writable<Reg>>,
    ) -> SmallInstVec<M::I> {
@@ -1150,7 +1291,7 @@ impl<M: ABIMachineSpec> Callee<M> {
                } => {
                    // However, we have to respect the extention mode for stack
                    // slots, or else we grab the wrong bytes on big-endian.
-                    let ext = M::get_ext_mode(self.sig.call_conv, extension);
+                    let ext = M::get_ext_mode(sigs[self.sig].call_conv, extension);
                    let ty = match (ext, ty_bits(ty) as u32) {
                        (ArgumentExtension::Uext, n) | (ArgumentExtension::Sext, n)
                            if n < M::word_bits() =>
@@ -1171,7 +1312,7 @@ impl<M: ABIMachineSpec> Callee<M> {
            }
        };

-        match &self.sig.args[idx] {
+        match &sigs[self.sig].args[idx] {
            &ABIArg::Slots { ref slots, .. } => {
                assert_eq!(into_regs.len(), slots.len());
                for (slot, into_reg) in slots.iter().zip(into_regs.regs().iter()) {
@@ -1233,12 +1374,13 @@ impl<M: ABIMachineSpec> Callee<M> {
    /// Generate an instruction which copies a source register to a return value slot.
    pub fn gen_copy_regs_to_retval(
        &self,
+        sigs: &SigSet,
        idx: usize,
        from_regs: ValueRegs<Writable<Reg>>,
    ) -> SmallInstVec<M::I> {
        let mut ret = smallvec![];
        let word_bits = M::word_bits() as u8;
-        match &self.sig.rets[idx] {
+        match &sigs[self.sig].rets[idx] {
            &ABIArg::Slots { ref slots, .. } => {
                assert_eq!(from_regs.len(), slots.len());
                for (slot, &from_reg) in slots.iter().zip(from_regs.regs().iter()) {
@@ -1247,7 +1389,7 @@ impl<M: ABIMachineSpec> Callee<M> {
                            reg, ty, extension, ..
                        } => {
                            let from_bits = ty_bits(ty) as u8;
-                            let ext = M::get_ext_mode(self.sig.call_conv, extension);
+                            let ext = M::get_ext_mode(sigs[self.sig].call_conv, extension);
                            let reg: Writable<Reg> = Writable::from_reg(Reg::from(reg));
                            match (ext, from_bits) {
                                (ArgumentExtension::Uext, n) | (ArgumentExtension::Sext, n)
@@ -1281,7 +1423,7 @@ impl<M: ABIMachineSpec> Callee<M> {
                            let off = i32::try_from(offset).expect(
                                "Argument stack offset greater than 2GB; should hit impl limit first",
                                );
-                            let ext = M::get_ext_mode(self.sig.call_conv, extension);
+                            let ext = M::get_ext_mode(sigs[self.sig].call_conv, extension);
                            // Trash the from_reg; it should be its last use.
                            match (ext, from_bits) {
                                (ArgumentExtension::Uext, n) | (ArgumentExtension::Sext, n)
@@ -1326,9 +1468,10 @@ impl<M: ABIMachineSpec> Callee<M> {
    /// values or an otherwise large return value that must be passed on the
    /// stack; typically the ABI specifies an extra hidden argument that is a
    /// pointer to that memory.
-    pub fn gen_retval_area_setup(&self) -> Option<M::I> {
-        if let Some(i) = self.sig.stack_ret_arg {
-            let insts = self.gen_copy_arg_to_regs(i, ValueRegs::one(self.ret_area_ptr.unwrap()));
+    pub fn gen_retval_area_setup(&self, sigs: &SigSet) -> Option<M::I> {
+        if let Some(i) = sigs[self.sig].stack_ret_arg {
+            let insts =
+                self.gen_copy_arg_to_regs(sigs, i, ValueRegs::one(self.ret_area_ptr.unwrap()));
            let inst = insts.into_iter().next().unwrap();
            trace!(
                "gen_retval_area_setup: inst {:?}; ptr reg is {:?}",
@@ -1343,9 +1486,9 @@ impl<M: ABIMachineSpec> Callee<M> {
    }

    /// Generate a return instruction.
-    pub fn gen_ret(&self) -> M::I {
+    pub fn gen_ret(&self, sigs: &SigSet) -> M::I {
        let mut rets = vec![];
-        for ret in &self.sig.rets {
+        for ret in &sigs[self.sig].rets {
            match ret {
                ABIArg::Slots { slots, .. } => {
                    for slot in slots {
@@ -1473,7 +1616,7 @@ impl<M: ABIMachineSpec> Callee<M> {
    /// other methods (`load_arg`, `store_retval`, and spillslot accesses.)
    /// `self` is mutable so that we can store information in it which will be
    /// useful when creating the epilogue.
-    pub fn gen_prologue(&mut self) -> SmallInstVec<M::I> {
+    pub fn gen_prologue(&mut self, sigs: &SigSet) -> SmallInstVec<M::I> {
        let bytes = M::word_bytes();
        let total_stacksize = self.stackslots_size + bytes * self.spillslots.unwrap() as u32;
        let mask = M::stack_align(self.call_conv) - 1;
@@ -1490,7 +1633,7 @@ impl<M: ABIMachineSpec> Callee<M> {
        self.setup_frame = self.flags.preserve_frame_pointers()
            || M::is_frame_setup_needed(
                self.is_leaf,
-                self.stack_args_size(),
+                self.stack_args_size(sigs),
                clobbered_callee_saves.len(),
                self.fixed_frame_storage_size,
            );
@@ -1597,8 +1740,8 @@ impl<M: ABIMachineSpec> Callee<M> {
    }

    /// Returns the size of arguments expected on the stack.
-    pub fn stack_args_size(&self) -> u32 {
-        self.sig.sized_stack_arg_space as u32
+    pub fn stack_args_size(&self, sigs: &SigSet) -> u32 {
+        sigs[self.sig].sized_stack_arg_space as u32
    }

    /// Get the spill-slot size.
@@ -1642,7 +1785,7 @@ impl<M: ABIMachineSpec> Callee<M> {
 /// ABI object for a callsite.
 pub struct Caller<M: ABIMachineSpec> {
    /// The called function's signature.
-    sig: ABISig,
+    sig: Sig,
    /// All uses for the callsite, i.e., function args.
    uses: SmallVec<[Reg; 8]>,
    /// All defs for the callsite, i.e., return values.
@@ -1673,15 +1816,15 @@ pub enum CallDest {
 impl<M: ABIMachineSpec> Caller<M> {
    /// Create a callsite ABI object for a call directly to the specified function.
    pub fn from_func(
-        sig: &ir::Signature,
+        sigs: &SigSet,
+        sig_ref: ir::SigRef,
        extname: &ir::ExternalName,
        dist: RelocDistance,
        caller_conv: isa::CallConv,
-        flags: &settings::Flags,
+        flags: settings::Flags,
    ) -> CodegenResult<Caller<M>> {
-        let ir_sig = ensure_struct_return_ptr_is_returned(sig);
-        let sig = ABISig::from_func_sig::<M>(&ir_sig, flags)?;
-        let (uses, defs, clobbers) = sig.call_uses_defs_clobbers::<M>();
+        let sig = sigs.abi_sig_for_sig_ref(sig_ref);
+        let (uses, defs, clobbers) = sigs[sig].call_uses_defs_clobbers::<M>();
        Ok(Caller {
            sig,
            uses,
@@ -1690,7 +1833,32 @@ impl<M: ABIMachineSpec> Caller<M> {
            dest: CallDest::ExtName(extname.clone(), dist),
            opcode: ir::Opcode::Call,
            caller_conv,
-            flags: flags.clone(),
+            flags,
+            _mach: PhantomData,
+        })
+    }
+
+    /// Create a callsite ABI object for a call directly to the specified
+    /// libcall.
+    pub fn from_libcall(
+        sigs: &SigSet,
+        sig: &ir::Signature,
+        extname: &ir::ExternalName,
+        dist: RelocDistance,
+        caller_conv: isa::CallConv,
+        flags: settings::Flags,
+    ) -> CodegenResult<Caller<M>> {
+        let sig = sigs.abi_sig_for_signature(sig);
+        let (uses, defs, clobbers) = sigs[sig].call_uses_defs_clobbers::<M>();
+        Ok(Caller {
+            sig,
+            uses,
+            defs,
+            clobbers,
+            dest: CallDest::ExtName(extname.clone(), dist),
+            opcode: ir::Opcode::Call,
+            caller_conv,
+            flags,
            _mach: PhantomData,
        })
    }
@@ -1698,15 +1866,15 @@ impl<M: ABIMachineSpec> Caller<M> {
    /// Create a callsite ABI object for a call to a function pointer with the
    /// given signature.
    pub fn from_ptr(
-        sig: &ir::Signature,
+        sigs: &SigSet,
+        sig_ref: ir::SigRef,
        ptr: Reg,
        opcode: ir::Opcode,
        caller_conv: isa::CallConv,
-        flags: &settings::Flags,
+        flags: settings::Flags,
    ) -> CodegenResult<Caller<M>> {
-        let ir_sig = ensure_struct_return_ptr_is_returned(sig);
-        let sig = ABISig::from_func_sig::<M>(&ir_sig, flags)?;
-        let (uses, defs, clobbers) = sig.call_uses_defs_clobbers::<M>();
+        let sig = sigs.abi_sig_for_sig_ref(sig_ref);
+        let (uses, defs, clobbers) = sigs[sig].call_uses_defs_clobbers::<M>();
        Ok(Caller {
            sig,
            uses,
@@ -1715,7 +1883,7 @@ impl<M: ABIMachineSpec> Caller<M> {
            dest: CallDest::Reg(ptr),
            opcode,
            caller_conv,
-            flags: flags.clone(),
+            flags,
            _mach: PhantomData,
        })
    }
@@ -1734,23 +1902,26 @@ fn adjust_stack_and_nominal_sp<M: ABIMachineSpec>(ctx: &mut Lower<M::I>, off: i3

 impl<M: ABIMachineSpec> Caller<M> {
    /// Get the number of arguments expected.
-    pub fn num_args(&self) -> usize {
-        if self.sig.stack_ret_arg.is_some() {
-            self.sig.args.len() - 1
+    pub fn num_args(&self, sigs: &SigSet) -> usize {
+        let data = &sigs[self.sig];
+        if data.stack_ret_arg.is_some() {
+            data.args.len() - 1
        } else {
-            self.sig.args.len()
+            data.args.len()
        }
    }

    /// Emit code to pre-adjust the stack, prior to argument copies and call.
    pub fn emit_stack_pre_adjust(&self, ctx: &mut Lower<M::I>) {
-        let off = self.sig.sized_stack_arg_space + self.sig.sized_stack_ret_space;
+        let off =
+            ctx.sigs()[self.sig].sized_stack_arg_space + ctx.sigs()[self.sig].sized_stack_ret_space;
        adjust_stack_and_nominal_sp::<M>(ctx, off as i32, /* is_sub = */ true)
    }

    /// Emit code to post-adjust the satck, after call return and return-value copies.
    pub fn emit_stack_post_adjust(&self, ctx: &mut Lower<M::I>) {
-        let off = self.sig.sized_stack_arg_space + self.sig.sized_stack_ret_space;
+        let off =
+            ctx.sigs()[self.sig].sized_stack_arg_space + ctx.sigs()[self.sig].sized_stack_ret_space;
        adjust_stack_and_nominal_sp::<M>(ctx, off as i32, /* is_sub = */ false)
    }

@@ -1765,7 +1936,7 @@ impl<M: ABIMachineSpec> Caller<M> {
        idx: usize,
        from_regs: ValueRegs<Reg>,
    ) {
-        match &self.sig.args[idx] {
+        match &ctx.sigs()[self.sig].args[idx] {
            &ABIArg::Slots { .. } => {}
            &ABIArg::StructArg { offset, size, .. } => {
                let src_ptr = from_regs.only_reg().unwrap();
@@ -1779,7 +1950,8 @@ impl<M: ABIMachineSpec> Caller<M> {
                // N.B.: because we process StructArg params *first*, this is
                // safe w.r.t. clobbers: we have not yet filled in any other
                // arg regs.
-                let memcpy_call_conv = isa::CallConv::for_libcall(&self.flags, self.sig.call_conv);
+                let memcpy_call_conv =
+                    isa::CallConv::for_libcall(&self.flags, ctx.sigs()[self.sig].call_conv);
                for insn in
                    M::gen_memcpy(memcpy_call_conv, dst_ptr.to_reg(), src_ptr, size as usize)
                        .into_iter()
@@ -1791,18 +1963,20 @@ impl<M: ABIMachineSpec> Caller<M> {
        }
    }

-    /// Emit a copy of an argument value from a source register, prior to the call.
-    /// For large arguments with associated stack buffer, this may load the address
-    /// of the buffer into the argument register, if required by the ABI.
-    pub fn emit_copy_regs_to_arg(
+    /// Generate a copy of an argument value from a source register, prior to
+    /// the call.  For large arguments with associated stack buffer, this may
+    /// load the address of the buffer into the argument register, if required
+    /// by the ABI.
+    pub fn gen_copy_regs_to_arg(
        &self,
-        ctx: &mut Lower<M::I>,
+        ctx: &Lower<M::I>,
        idx: usize,
        from_regs: ValueRegs<Reg>,
-    ) {
+    ) -> SmallInstVec<M::I> {
+        let mut insts = smallvec![];
        let word_rc = M::word_reg_class();
        let word_bits = M::word_bits() as usize;
-        match &self.sig.args[idx] {
+        match &ctx.sigs()[self.sig].args[idx] {
            &ABIArg::Slots { ref slots, .. } => {
                assert_eq!(from_regs.len(), slots.len());
                for (slot, from_reg) in slots.iter().zip(from_regs.regs().iter()) {
@@ -1810,7 +1984,7 @@ impl<M: ABIMachineSpec> Caller<M> {
                        &ABIArgSlot::Reg {
                            reg, ty, extension, ..
                        } => {
-                            let ext = M::get_ext_mode(self.sig.call_conv, extension);
+                            let ext = M::get_ext_mode(ctx.sigs()[self.sig].call_conv, extension);
                            if ext != ir::ArgumentExtension::None && ty_bits(ty) < word_bits {
                                assert_eq!(word_rc, reg.class());
                                let signed = match ext {
@@ -1818,7 +1992,7 @@ impl<M: ABIMachineSpec> Caller<M> {
                                    ir::ArgumentExtension::Sext => true,
                                    _ => unreachable!(),
                                };
-                                ctx.emit(M::gen_extend(
+                                insts.push(M::gen_extend(
                                    Writable::from_reg(Reg::from(reg)),
                                    *from_reg,
                                    signed,
@@ -1826,7 +2000,7 @@ impl<M: ABIMachineSpec> Caller<M> {
                                    word_bits as u8,
                                ));
                            } else {
-                                ctx.emit(M::gen_move(
+                                insts.push(M::gen_move(
                                    Writable::from_reg(Reg::from(reg)),
                                    *from_reg,
                                    ty,
@@ -1840,7 +2014,7 @@ impl<M: ABIMachineSpec> Caller<M> {
                            ..
                        } => {
                            let mut ty = ty;
-                            let ext = M::get_ext_mode(self.sig.call_conv, extension);
+                            let ext = M::get_ext_mode(ctx.sigs()[self.sig].call_conv, extension);
                            if ext != ir::ArgumentExtension::None && ty_bits(ty) < word_bits {
                                assert_eq!(word_rc, from_reg.class());
                                let signed = match ext {
@@ -1851,7 +2025,7 @@ impl<M: ABIMachineSpec> Caller<M> {
                                // Extend in place in the source register. Our convention is to
                                // treat high bits as undefined for values in registers, so this
                                // is safe, even for an argument that is nominally read-only.
-                                ctx.emit(M::gen_extend(
+                                insts.push(M::gen_extend(
                                    Writable::from_reg(*from_reg),
                                    *from_reg,
                                    signed,
@@ -1861,7 +2035,7 @@ impl<M: ABIMachineSpec> Caller<M> {
                                // Store the extended version.
                                ty = M::word_type();
                            }
-                            ctx.emit(M::gen_store_stack(
+                            insts.push(M::gen_store_stack(
                                StackAMode::SPOffset(offset, ty),
                                *from_reg,
                                ty,
@@ -1875,16 +2049,18 @@ impl<M: ABIMachineSpec> Caller<M> {
            }
            &ABIArg::ImplicitPtrArg { .. } => unimplemented!(), // Only supported via ISLE.
        }
+        insts
    }

    /// Emit a copy a return value into a destination register, after the call returns.
-    pub fn emit_copy_retval_to_regs(
+    pub fn gen_copy_retval_to_regs(
        &self,
-        ctx: &mut Lower<M::I>,
+        ctx: &Lower<M::I>,
        idx: usize,
        into_regs: ValueRegs<Writable<Reg>>,
-    ) {
-        match &self.sig.rets[idx] {
+    ) -> SmallInstVec<M::I> {
+        let mut insts = smallvec![];
+        match &ctx.sigs()[self.sig].rets[idx] {
            &ABIArg::Slots { ref slots, .. } => {
                assert_eq!(into_regs.len(), slots.len());
                for (slot, into_reg) in slots.iter().zip(into_regs.regs().iter()) {
@@ -1892,11 +2068,11 @@ impl<M: ABIMachineSpec> Caller<M> {
                        // Extension mode doesn't matter because we're copying out, not in,
                        // and we ignore high bits in our own registers by convention.
                        &ABIArgSlot::Reg { reg, ty, .. } => {
-                            ctx.emit(M::gen_move(*into_reg, Reg::from(reg), ty));
+                            insts.push(M::gen_move(*into_reg, Reg::from(reg), ty));
                        }
                        &ABIArgSlot::Stack { offset, ty, .. } => {
-                            let ret_area_base = self.sig.sized_stack_arg_space;
-                            ctx.emit(M::gen_load_stack(
+                            let ret_area_base = ctx.sigs()[self.sig].sized_stack_arg_space;
+                            insts.push(M::gen_load_stack(
                                StackAMode::SPOffset(offset + ret_area_base, ty),
                                *into_reg,
                                ty,
@@ -1912,6 +2088,7 @@ impl<M: ABIMachineSpec> Caller<M> {
                panic!("ImplicitPtrArg not supported in return position");
            }
        }
+        insts
    }

    /// Emit the call itself.
@@ -1933,15 +2110,17 @@ impl<M: ABIMachineSpec> Caller<M> {
            mem::replace(&mut self.defs, Default::default()),
        );
        let word_type = M::word_type();
-        if let Some(i) = self.sig.stack_ret_arg {
+        if let Some(i) = ctx.sigs()[self.sig].stack_ret_arg {
            let rd = ctx.alloc_tmp(word_type).only_reg().unwrap();
-            let ret_area_base = self.sig.sized_stack_arg_space;
+            let ret_area_base = ctx.sigs()[self.sig].sized_stack_arg_space;
            ctx.emit(M::gen_get_stack_addr(
                StackAMode::SPOffset(ret_area_base, I8),
                rd,
                I8,
            ));
-            self.emit_copy_regs_to_arg(ctx, i, ValueRegs::one(rd.to_reg()));
+            for inst in self.gen_copy_regs_to_arg(ctx, i, ValueRegs::one(rd.to_reg())) {
+                ctx.emit(inst);
+            }
        }
        let tmp = ctx.alloc_tmp(word_type).only_reg().unwrap();
        for inst in M::gen_call(
@@ -1951,7 +2130,7 @@ impl<M: ABIMachineSpec> Caller<M> {
            self.clobbers,
            self.opcode,
            tmp,
-            self.sig.call_conv,
+            ctx.sigs()[self.sig].call_conv,
            self.caller_conv,
        )
        .into_iter()