Add early-stage optimization crate (#556)

* Add simple constant folding and folding tests

cranelift/Cargo.toml

@@ -25,6 +25,7 @@ cranelift-filetests = { path = "lib/filetests", version = "0.22.0" }
 cranelift-module = { path = "lib/module", version = "0.22.0" }
 cranelift-faerie = { path = "lib/faerie", version = "0.22.0" }
 cranelift-simplejit = { path = "lib/simplejit", version = "0.22.0" }
+cranelift-preopt = { path = "lib/preopt", version = "0.22.0" }
 cranelift = { path = "lib/umbrella", version = "0.22.0" }
 filecheck = "0.4.0"
 clap = "2.32.0"

cranelift/filetests/preopt/branch.clif

@@ -0,0 +1,54 @@
+test preopt
+target x86_64
+
+function %brz_fold() -> i32 {
+ebb0:
+    v0 = bconst.b1 false
+    brz v0, ebb2
+    jump ebb1
+ebb1:
+    v1 = iconst.i32 42
+    return v1
+ebb2:
+    v2 = iconst.i32 24
+    return v2
+}
+; sameln: function %brz_fold
+; nextln: ebb0:
+; nextln:     v0 = bconst.b1 false
+; nextln:     jump ebb2
+; nextln: 
+; nextln: ebb1:
+; nextln:     v1 = iconst.i32 42
+; nextln:     return v1
+; nextln: 
+; nextln: ebb2:
+; nextln:     v2 = iconst.i32 24
+; nextln:     return v2
+; nextln: }
+
+function %brnz_fold() -> i32 {
+ebb0:
+    v0 = bconst.b1 true
+    brnz v0, ebb2
+    jump ebb1
+ebb1:
+    v1 = iconst.i32 42
+    return v1
+ebb2:
+    v2 = iconst.i32 24
+    return v2
+}
+; sameln: function %brnz_fold
+; nextln: ebb0:
+; nextln:     v0 = bconst.b1 true
+; nextln:     jump ebb2
+; nextln: 
+; nextln: ebb1:
+; nextln:     v1 = iconst.i32 42
+; nextln:     return v1
+; nextln: 
+; nextln: ebb2:
+; nextln:     v2 = iconst.i32 24
+; nextln:     return v2
+; nextln: }

cranelift/filetests/preopt/numerical.clif

@@ -0,0 +1,36 @@
+test preopt
+target x86_64
+
+function %iadd_fold() -> i32 {
+ebb0:
+    v0 = iconst.i32 37
+    v1 = iconst.i32 5
+    v2 = iadd v0, v1
+    v3 = iconst.i32 8
+    v4 = iadd v2, v3
+    return v4
+}
+; sameln: function %iadd_fold
+; nextln: ebb0:
+; nextln:     v0 = iconst.i32 37
+; nextln:     v1 = iconst.i32 5
+; nextln:     v2 = iconst.i32 42
+; nextln:     v3 = iconst.i32 8
+; nextln:     v4 = iconst.i32 50
+; nextln:     return v4
+; nextln: }
+
+function %isub_fold() -> i32 {
+ebb0:
+    v0 = iconst.i32 42
+    v1 = iconst.i32 1
+    v2 = isub v0, v1
+    return v2
+}
+; sameln: function %isub_fold
+; nextln: ebb0:
+; nextln:     v0 = iconst.i32 42
+; nextln:     v1 = iconst.i32 1
+; nextln:     v2 = iconst.i32 41
+; nextln:     return v2
+; nextln: }

cranelift/filetests/simple_preopt/div_by_const_indirect.clif

@@ -1,4 +1,4 @@
-test preopt
+test simple_preopt
 target i686 baseline
 
 ; Cases where the denominator is created by an iconst

cranelift/filetests/simple_preopt/div_by_const_non_power_of_2.clif

@@ -1,4 +1,4 @@
-test preopt
+test simple_preopt
 target i686 baseline
 
 ; -------- U32 --------

cranelift/filetests/simple_preopt/div_by_const_power_of_2.clif

@@ -1,4 +1,4 @@
-test preopt
+test simple_preopt
 target i686 baseline
 
 ; -------- U32 --------

cranelift/filetests/simple_preopt/rem_by_const_non_power_of_2.clif

@@ -1,4 +1,4 @@
-test preopt
+test simple_preopt
 target i686 baseline
 
 ; -------- U32 --------

cranelift/filetests/simple_preopt/rem_by_const_power_of_2.clif

@@ -1,4 +1,4 @@
-test preopt
+test simple_preopt
 target i686 baseline
 
 ; -------- U32 --------

cranelift/filetests/simple_preopt/simplify.clif

@@ -1,4 +1,4 @@
-test preopt
+test simple_preopt
 target i686
 
 function %iadd_imm(i32) -> i32 {

lib/codegen/src/context.rs

@@ -22,11 +22,11 @@ use licm::do_licm;
 use loop_analysis::LoopAnalysis;
 use nan_canonicalization::do_nan_canonicalization;
 use postopt::do_postopt;
-use preopt::do_preopt;
 use regalloc;
 use result::CodegenResult;
 use settings::{FlagsOrIsa, OptLevel};
 use simple_gvn::do_simple_gvn;
+use simple_preopt::do_preopt;
 use std::vec::Vec;
 use timing;
 use unreachable_code::eliminate_unreachable_code;

lib/codegen/src/lib.rs

@@ -104,12 +104,12 @@ mod nan_canonicalization;
 mod partition_slice;
 mod postopt;
 mod predicates;
-mod preopt;
 mod ref_slice;
 mod regalloc;
 mod result;
 mod scoped_hash_map;
 mod simple_gvn;
+mod simple_preopt;
 mod stack_layout;
 mod topo_order;
 mod unreachable_code;

lib/codegen/src/timing.rs

@@ -124,7 +124,7 @@ mod details {
     }
 
     /// Accumulated timing information for a single pass.
-    #[derive(Default)]
+    #[derive(Default, Copy, Clone)]
     struct PassTime {
         /// Total time spent running this pass including children.
         total: Duration,
@@ -134,17 +134,24 @@ mod details {
     }
 
     /// Accumulated timing for all passes.
-    #[derive(Default)]
     pub struct PassTimes {
         pass: [PassTime; NUM_PASSES],
     }
 
+    impl Default for PassTimes {
+        fn default() -> Self {
+            PassTimes {
+                pass: [Default::default(); NUM_PASSES],
+            }
+        }
+    }
+
     impl fmt::Display for PassTimes {
         fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
             writeln!(f, "======== ========  ==================================")?;
             writeln!(f, "   Total     Self  Pass")?;
             writeln!(f, "-------- --------  ----------------------------------")?;
-            for (time, desc) in self.pass.iter().zip(&DESCRIPTIONS) {
+            for (time, desc) in self.pass.iter().zip(&DESCRIPTIONS[..]) {
                 // Omit passes that haven't run.
                 if time.total == Duration::default() {
                     continue;
@@ -212,7 +219,7 @@ mod details {
     /// Add `timings` to the accumulated timings for the current thread.
     pub fn add_to_current(times: &PassTimes) {
         PASS_TIME.with(|rc| {
-            for (a, b) in rc.borrow_mut().pass.iter_mut().zip(&times.pass) {
+            for (a, b) in rc.borrow_mut().pass.iter_mut().zip(&times.pass[..]) {
                 a.total += b.total;
                 a.child += b.child;
             }

lib/filetests/Cargo.toml

@@ -11,6 +11,7 @@ publish = false
 [dependencies]
 cranelift-codegen = { path = "../codegen", version = "0.22.0", features = ["testing_hooks"] }
 cranelift-reader = { path = "../reader", version = "0.22.0" }
+cranelift-preopt = { path = "../preopt", version = "0.22.0" }
 file-per-thread-logger = "0.1.1"
 filecheck = "0.4.0"
 num_cpus = "1.8.0"

lib/filetests/src/lib.rs

@@ -24,6 +24,7 @@
 )]
 
 extern crate cranelift_codegen;
+extern crate cranelift_preopt;
 extern crate cranelift_reader;
 extern crate file_per_thread_logger;
 extern crate filecheck;
@@ -56,6 +57,7 @@ mod test_print_cfg;
 mod test_regalloc;
 mod test_shrink;
 mod test_simple_gvn;
+mod test_simple_preopt;
 mod test_verifier;
 
 /// The result of running the test in a file.
@@ -127,12 +129,13 @@ fn new_subtest(parsed: &TestCommand) -> subtest::SubtestResult<Box<subtest::SubT
         "legalizer" => test_legalizer::subtest(parsed),
         "licm" => test_licm::subtest(parsed),
         "postopt" => test_postopt::subtest(parsed),
-        "preopt" => test_preopt::subtest(parsed),
+        "simple_preopt" => test_simple_preopt::subtest(parsed),
         "print-cfg" => test_print_cfg::subtest(parsed),
         "regalloc" => test_regalloc::subtest(parsed),
         "shrink" => test_shrink::subtest(parsed),
         "simple-gvn" => test_simple_gvn::subtest(parsed),
         "verifier" => test_verifier::subtest(parsed),
+        "preopt" => test_preopt::subtest(parsed),
         _ => Err(format!("unknown test command '{}'", parsed.command)),
     }
 }

lib/filetests/src/test_preopt.rs

@@ -1,10 +1,14 @@
-//! Test command for testing the preopt pass.
+//! Test command for testing the constant folding pass.
+//!
+//! The `dce` test command runs each function through the constant folding pass after ensuring
+//! that all instructions are legal for the target.
 //!
 //! The resulting function is sent to `filecheck`.
 
 use cranelift_codegen;
 use cranelift_codegen::ir::Function;
 use cranelift_codegen::print_errors::pretty_error;
+use cranelift_preopt::optimize;
 use cranelift_reader::TestCommand;
 use std::borrow::Cow;
 use subtest::{run_filecheck, Context, SubTest, SubtestResult};
@@ -29,16 +33,18 @@ impl SubTest for TestPreopt {
         true
     }
 
-    fn run(&self, func: Cow<Function>, context: &Context) -> SubtestResult<()> {
+    fn needs_isa(&self) -> bool {
-        let mut comp_ctx = cranelift_codegen::Context::for_function(func.into_owned());
+        true
-        let isa = context.isa.expect("preopt needs an ISA");
+    }
 
-        comp_ctx.flowgraph();
+    fn run(&self, func: Cow<Function>, context: &Context) -> SubtestResult<()> {
-        comp_ctx
+        let isa = context.isa.expect("compile needs an ISA");
-            .preopt(isa)
+        let mut comp_ctx = cranelift_codegen::Context::for_function(func.into_owned());
+
+        optimize(&mut comp_ctx, isa)
             .map_err(|e| pretty_error(&comp_ctx.func, context.isa, Into::into(e)))?;
 
-        let text = &comp_ctx.func.display(isa).to_string();
+        let text = comp_ctx.func.display(context.isa).to_string();
         run_filecheck(&text, context)
     }
 }

lib/filetests/src/test_simple_preopt.rs

@@ -0,0 +1,44 @@
+//! Test command for testing the preopt pass.
+//!
+//! The resulting function is sent to `filecheck`.
+
+use cranelift_codegen;
+use cranelift_codegen::ir::Function;
+use cranelift_codegen::print_errors::pretty_error;
+use cranelift_reader::TestCommand;
+use std::borrow::Cow;
+use subtest::{run_filecheck, Context, SubTest, SubtestResult};
+
+struct TestSimplePreopt;
+
+pub fn subtest(parsed: &TestCommand) -> SubtestResult<Box<SubTest>> {
+    assert_eq!(parsed.command, "simple_preopt");
+    if !parsed.options.is_empty() {
+        Err(format!("No options allowed on {}", parsed))
+    } else {
+        Ok(Box::new(TestSimplePreopt))
+    }
+}
+
+impl SubTest for TestSimplePreopt {
+    fn name(&self) -> &'static str {
+        "simple_preopt"
+    }
+
+    fn is_mutating(&self) -> bool {
+        true
+    }
+
+    fn run(&self, func: Cow<Function>, context: &Context) -> SubtestResult<()> {
+        let mut comp_ctx = cranelift_codegen::Context::for_function(func.into_owned());
+        let isa = context.isa.expect("preopt needs an ISA");
+
+        comp_ctx.flowgraph();
+        comp_ctx
+            .preopt(isa)
+            .map_err(|e| pretty_error(&comp_ctx.func, context.isa, Into::into(e)))?;
+
+        let text = &comp_ctx.func.display(isa).to_string();
+        run_filecheck(&text, context)
+    }
+}

lib/preopt/Cargo.toml

@@ -0,0 +1,27 @@
+[package]
+authors = ["The Cranelift Project Developers"]
+name = "cranelift-preopt"
+version = "0.22.0"
+description = "Support for optimizations in Cranelift"
+license = "Apache-2.0 WITH LLVM-exception"
+documentation = "https://cranelift.readthedocs.io/"
+repository = "https://github.com/CraneStation/cranelift"
+categories = ["no_std"]
+readme = "README.md"
+keywords = ["optimize", "compile", "compiler", "jit"]
+
+[dependencies]
+cranelift-codegen = { path = "../codegen", version = "0.22.0", default-features = false }
+cranelift-entity = { path = "../entity", version = "0.22.0", default-features = false }
+# This is commented out because it doesn't build on Rust 1.25.0, which
+# cranelift currently supports.
+# rustc_apfloat = { version = "0.1.2", default-features = false }
+
+[features]
+default = ["std"]
+std = ["cranelift-codegen/std", "cranelift-entity/std"]
+core = ["cranelift-codegen/core"]
+
+[badges]
+maintenance = { status = "experimental" }
+travis-ci = { repository = "CraneStation/cranelift" }

lib/preopt/LICENSE

@@ -0,0 +1,219 @@
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lib/preopt/README.md

@@ -0,0 +1 @@
+This crate performes early-stage optimizations on [Cranelift](https://crates.io/crates/cranelift) IR.

lib/preopt/src/constant_folding.rs

@@ -0,0 +1,254 @@
+//! Fold operations on constants at compile time.
+
+use cranelift_codegen::{
+    cursor::{Cursor, FuncCursor},
+    ir::{self, InstBuilder},
+};
+// use rustc_apfloat::{
+//     ieee::{Double, Single},
+//     Float,
+// };
+
+enum ConstImm {
+    Bool(bool),
+    I64(i64),
+    Ieee32(f32), // Ieee32 and Ieee64 will be replaced with `Single` and `Double` from the rust_apfloat library eventually.
+    Ieee64(f64),
+}
+
+impl ConstImm {
+    fn unwrap_i64(self) -> i64 {
+        if let ConstImm::I64(imm) = self {
+            imm
+        } else {
+            panic!("self did not contain an `i64`.")
+        }
+    }
+
+    fn evaluate_truthiness(self) -> bool {
+        match self {
+            ConstImm::Bool(b) => b,
+            ConstImm::I64(imm) => imm != 0,
+            _ => panic!(
+                "Only a `ConstImm::Bool` and `ConstImm::I64` can be evaluated for \"truthiness\""
+            ),
+        }
+    }
+}
+
+/// Fold operations on constants.
+///
+/// It's important to note that this will not remove unused constants. It's
+/// assumed that the DCE pass will take care of them.
+pub fn fold_constants(func: &mut ir::Function) {
+    let mut pos = FuncCursor::new(func);
+
+    while let Some(_ebb) = pos.next_ebb() {
+        while let Some(inst) = pos.next_inst() {
+            use self::ir::InstructionData::*;
+            match pos.func.dfg[inst] {
+                Binary { opcode, args } => {
+                    fold_binary(&mut pos.func.dfg, inst, opcode, args);
+                }
+                Unary { opcode, arg } => {
+                    fold_unary(&mut pos.func.dfg, inst, opcode, arg);
+                }
+                Branch {
+                    opcode,
+                    args: _,
+                    destination: _,
+                } => {
+                    fold_branch(&mut pos, inst, opcode);
+                }
+                _ => {}
+            }
+        }
+    }
+}
+
+fn resolve_value_to_imm(dfg: &ir::DataFlowGraph, value: ir::Value) -> Option<ConstImm> {
+    let original = dfg.resolve_aliases(value);
+
+    let inst = dfg.value_def(original).unwrap_inst();
+
+    use self::ir::{InstructionData::*, Opcode::*};
+    match dfg[inst] {
+        UnaryImm {
+            opcode: Iconst,
+            imm,
+        } => Some(ConstImm::I64(imm.into())),
+        UnaryIeee32 {
+            opcode: F32const,
+            imm,
+        } => {
+            // See https://doc.rust-lang.org/std/primitive.f32.html#method.from_bits for caveats.
+            let ieee_f32 = f32::from_bits(imm.bits());
+            Some(ConstImm::Ieee32(ieee_f32))
+        }
+        UnaryIeee64 {
+            opcode: F64const,
+            imm,
+        } => {
+            // See https://doc.rust-lang.org/std/primitive.f32.html#method.from_bits for caveats.
+            let ieee_f64 = f64::from_bits(imm.bits());
+            Some(ConstImm::Ieee64(ieee_f64))
+        }
+        UnaryBool {
+            opcode: Bconst,
+            imm,
+        } => Some(ConstImm::Bool(imm)),
+        _ => None,
+    }
+}
+
+fn evaluate_binary(opcode: ir::Opcode, imm0: ConstImm, imm1: ConstImm) -> Option<ConstImm> {
+    use std::num::Wrapping;
+
+    match opcode {
+        ir::Opcode::Iadd => {
+            let imm0 = Wrapping(imm0.unwrap_i64());
+            let imm1 = Wrapping(imm1.unwrap_i64());
+            Some(ConstImm::I64((imm0 + imm1).0))
+        }
+        ir::Opcode::Isub => {
+            let imm0 = Wrapping(imm0.unwrap_i64());
+            let imm1 = Wrapping(imm1.unwrap_i64());
+            Some(ConstImm::I64((imm0 - imm1).0))
+        }
+        ir::Opcode::Imul => {
+            let imm0 = Wrapping(imm0.unwrap_i64());
+            let imm1 = Wrapping(imm1.unwrap_i64());
+            Some(ConstImm::I64((imm0 * imm1).0))
+        }
+        ir::Opcode::Udiv => {
+            let imm0 = Wrapping(imm0.unwrap_i64());
+            let imm1 = Wrapping(imm1.unwrap_i64());
+            if imm1.0 == 0 {
+                panic!("Cannot divide by a zero.")
+            }
+            Some(ConstImm::I64((imm0 / imm1).0))
+        }
+        ir::Opcode::Fadd => match (imm0, imm1) {
+            (ConstImm::Ieee32(imm0), ConstImm::Ieee32(imm1)) => Some(ConstImm::Ieee32(imm0 + imm1)),
+            (ConstImm::Ieee64(imm0), ConstImm::Ieee64(imm1)) => Some(ConstImm::Ieee64(imm0 + imm1)),
+            _ => unreachable!(),
+        },
+        ir::Opcode::Fsub => match (imm0, imm1) {
+            (ConstImm::Ieee32(imm0), ConstImm::Ieee32(imm1)) => Some(ConstImm::Ieee32(imm0 - imm1)),
+            (ConstImm::Ieee64(imm0), ConstImm::Ieee64(imm1)) => Some(ConstImm::Ieee64(imm0 - imm1)),
+            _ => unreachable!(),
+        },
+        ir::Opcode::Fmul => match (imm0, imm1) {
+            (ConstImm::Ieee32(imm0), ConstImm::Ieee32(imm1)) => Some(ConstImm::Ieee32(imm0 * imm1)),
+            (ConstImm::Ieee64(imm0), ConstImm::Ieee64(imm1)) => Some(ConstImm::Ieee64(imm0 * imm1)),
+            _ => unreachable!(),
+        },
+        ir::Opcode::Fdiv => match (imm0, imm1) {
+            (ConstImm::Ieee32(imm0), ConstImm::Ieee32(imm1)) => Some(ConstImm::Ieee32(imm0 / imm1)),
+            (ConstImm::Ieee64(imm0), ConstImm::Ieee64(imm1)) => Some(ConstImm::Ieee64(imm0 / imm1)),
+            _ => unreachable!(),
+        },
+        _ => None,
+    }
+}
+
+fn evaluate_unary(opcode: ir::Opcode, imm: ConstImm) -> Option<ConstImm> {
+    match opcode {
+        ir::Opcode::Fneg => match imm {
+            ConstImm::Ieee32(imm) => Some(ConstImm::Ieee32(-imm)),
+            ConstImm::Ieee64(imm) => Some(ConstImm::Ieee64(-imm)),
+            _ => unreachable!(),
+        },
+        ir::Opcode::Fabs => match imm {
+            ConstImm::Ieee32(imm) => Some(ConstImm::Ieee32(imm.abs())),
+            ConstImm::Ieee64(imm) => Some(ConstImm::Ieee64(imm.abs())),
+            _ => unreachable!(),
+        },
+        _ => None,
+    }
+}
+
+fn replace_inst(dfg: &mut ir::DataFlowGraph, inst: ir::Inst, const_imm: ConstImm) {
+    use self::ConstImm::*;
+    match const_imm {
+        I64(imm) => {
+            let typevar = dfg.ctrl_typevar(inst);
+            dfg.replace(inst).iconst(typevar, imm);
+        }
+        Ieee32(imm) => {
+            dfg.replace(inst)
+                .f32const(ir::immediates::Ieee32::with_bits(imm.to_bits()));
+        }
+        Ieee64(imm) => {
+            dfg.replace(inst)
+                .f64const(ir::immediates::Ieee64::with_bits(imm.to_bits()));
+        }
+        Bool(imm) => {
+            let typevar = dfg.ctrl_typevar(inst);
+            dfg.replace(inst).bconst(typevar, imm);
+        }
+    }
+}
+
+/// Fold a binary instruction.
+fn fold_binary(
+    dfg: &mut ir::DataFlowGraph,
+    inst: ir::Inst,
+    opcode: ir::Opcode,
+    args: [ir::Value; 2],
+) {
+    let (imm0, imm1) = if let (Some(imm0), Some(imm1)) = (
+        resolve_value_to_imm(dfg, args[0]),
+        resolve_value_to_imm(dfg, args[1]),
+    ) {
+        (imm0, imm1)
+    } else {
+        return;
+    };
+
+    if let Some(const_imm) = evaluate_binary(opcode, imm0, imm1) {
+        replace_inst(dfg, inst, const_imm);
+    }
+}
+
+/// Fold a unary instruction.
+fn fold_unary(dfg: &mut ir::DataFlowGraph, inst: ir::Inst, opcode: ir::Opcode, arg: ir::Value) {
+    let imm = if let Some(imm) = resolve_value_to_imm(dfg, arg) {
+        imm
+    } else {
+        return;
+    };
+
+    if let Some(const_imm) = evaluate_unary(opcode, imm) {
+        replace_inst(dfg, inst, const_imm);
+    }
+}
+
+fn fold_branch(pos: &mut FuncCursor, inst: ir::Inst, opcode: ir::Opcode) {
+    let (cond, ebb, args) = {
+        let values = pos.func.dfg.inst_args(inst);
+        let inst_data = &pos.func.dfg[inst];
+        (
+            resolve_value_to_imm(&pos.func.dfg, values[0]).unwrap(),
+            inst_data.branch_destination().unwrap(),
+            values[1..].to_vec(),
+        )
+    };
+
+    let truthiness = cond.evaluate_truthiness();
+    let branch_if_zero = match opcode {
+        ir::Opcode::Brz => true,
+        ir::Opcode::Brnz => false,
+        _ => unreachable!(),
+    };
+
+    if (branch_if_zero && !truthiness) || (!branch_if_zero && truthiness) {
+        pos.func.dfg.replace(inst).jump(ebb, &args);
+        // remove the rest of the ebb to avoid verifier errors
+        while let Some(next_inst) = pos.func.layout.next_inst(inst) {
+            pos.func.layout.remove_inst(next_inst);
+        }
+    } else {
+        pos.remove_inst_and_step_back();
+    }
+}

lib/preopt/src/lib.rs

@@ -0,0 +1,71 @@
+//! Performes early-stage optimizations on Cranelift IR.
+
+#![deny(
+    missing_docs,
+    trivial_numeric_casts,
+    unused_extern_crates,
+    unstable_features
+)]
+#![warn(unused_import_braces)]
+#![cfg_attr(
+    feature = "clippy",
+    plugin(clippy(conf_file = "../../clippy.toml"))
+)]
+#![cfg_attr(
+    feature = "cargo-clippy",
+    allow(new_without_default, new_without_default_derive)
+)]
+#![cfg_attr(
+    feature = "cargo-clippy",
+    warn(
+        float_arithmetic,
+        mut_mut,
+        nonminimal_bool,
+        option_map_unwrap_or,
+        option_map_unwrap_or_else,
+        print_stdout,
+        unicode_not_nfc,
+        use_self
+    )
+)]
+#![cfg_attr(not(feature = "std"), no_std)]
+#![cfg_attr(not(feature = "std"), alloc)]
+
+#[cfg(not(feature = "std"))]
+extern crate alloc;
+
+extern crate cranelift_codegen;
+// extern crate rustc_apfloat;
+
+mod constant_folding;
+
+use cranelift_codegen::{isa::TargetIsa, settings::FlagsOrIsa, CodegenResult, Context};
+
+/// Optimize the function with available optimizations.
+///
+/// Since this can be resource intensive (and code-size inflating),
+/// it is separated from `Context::compile` to allow DCE to remove it
+/// if it's not used.
+pub fn optimize(ctx: &mut Context, isa: &TargetIsa) -> CodegenResult<()> {
+    ctx.verify_if(isa)?;
+    fold_constants(ctx, isa)?;
+
+    Ok(())
+}
+
+/// Fold constants
+pub fn fold_constants<'a, FOI>(ctx: &mut Context, fisa: FOI) -> CodegenResult<()>
+where
+    FOI: Into<FlagsOrIsa<'a>>,
+{
+    constant_folding::fold_constants(&mut ctx.func);
+    ctx.verify_if(fisa)?;
+    Ok(())
+}
+
+/// This replaces `std` in builds with `core`.
+#[cfg(not(feature = "std"))]
+mod std {
+    pub use alloc::{boxed, slice, string, vec};
+    pub use core::*;
+}