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Rollup merge of #108246 - saethlin:instcombine-redundant-casts, r=compiler-errors

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Add an InstCombine for redundant casts

`@rustbot` label +A-mir-opt
This commit is contained in:
Guillaume Gomez 2023-02-22 10:35:09 +01:00 committed by GitHub
commit 4658210565
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5 changed files with 80 additions and 0 deletions
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9
compiler/rustc_mir_transform/src/instcombine.rs
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@ -30,6 +30,7 @@ impl<'tcx> MirPass<'tcx> for InstCombine {
ctx.combine_bool_cmp(&statement.source_info, rvalue);
ctx.combine_ref_deref(&statement.source_info, rvalue);
ctx.combine_len(&statement.source_info, rvalue);
ctx.combine_cast(&statement.source_info, rvalue);
}
_ => {}
}
@ -142,6 +143,14 @@ impl<'tcx> InstCombineContext<'tcx, '_> {
}
}
fn combine_cast(&self, _source_info: &SourceInfo, rvalue: &mut Rvalue<'tcx>) {
if let Rvalue::Cast(_kind, operand, ty) = rvalue {
if operand.ty(self.local_decls, self.tcx) == *ty {
*rvalue = Rvalue::Use(operand.clone());
}
}
}
fn combine_primitive_clone(
&self,
terminator: &mut Terminator<'tcx>,

25
tests/mir-opt/casts.redundant.InstCombine.diff Normal file
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@ -0,0 +1,25 @@
- // MIR for `redundant` before InstCombine
+ // MIR for `redundant` after InstCombine
fn redundant(_1: *const &u8) -> *const &u8 {
debug x => _1; // in scope 0 at $DIR/casts.rs:+0:30: +0:31
let mut _0: *const &u8; // return place in scope 0 at $DIR/casts.rs:+0:51: +0:64
let mut _2: *const &u8; // in scope 0 at $DIR/casts.rs:+1:5: +1:55
let mut _3: *const &u8; // in scope 0 at $DIR/casts.rs:+1:36: +1:37
scope 1 (inlined generic_cast::<&u8, &u8>) { // at $DIR/casts.rs:6:5: 6:38
debug x => _3; // in scope 1 at $DIR/casts.rs:10:23: 10:24
}
bb0: {
StorageLive(_2); // scope 0 at $DIR/casts.rs:+1:5: +1:55
StorageLive(_3); // scope 0 at $DIR/casts.rs:+1:36: +1:37
_3 = _1; // scope 0 at $DIR/casts.rs:+1:36: +1:37
- _2 = _3 as *const &u8 (PtrToPtr); // scope 1 at $DIR/casts.rs:11:5: 11:18
+ _2 = _3; // scope 1 at $DIR/casts.rs:11:5: 11:18
StorageDead(_3); // scope 0 at $DIR/casts.rs:+1:37: +1:38
_0 = _2; // scope 0 at $DIR/casts.rs:+1:5: +1:55
StorageDead(_2); // scope 0 at $DIR/casts.rs:+2:1: +2:2
return; // scope 0 at $DIR/casts.rs:+2:2: +2:2
}
}

14
tests/mir-opt/casts.redundant.PreCodegen.after.mir Normal file
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@ -0,0 +1,14 @@
// MIR for `redundant` after PreCodegen
fn redundant(_1: *const &u8) -> *const &u8 {
debug x => _1; // in scope 0 at $DIR/casts.rs:+0:30: +0:31
let mut _0: *const &u8; // return place in scope 0 at $DIR/casts.rs:+0:51: +0:64
scope 1 (inlined generic_cast::<&u8, &u8>) { // at $DIR/casts.rs:6:5: 6:38
debug x => _1; // in scope 1 at $DIR/casts.rs:10:23: 10:24
}
bb0: {
_0 = _1; // scope 0 at $DIR/casts.rs:+1:5: +1:55
return; // scope 0 at $DIR/casts.rs:+2:2: +2:2
}
}

15
tests/mir-opt/casts.roundtrip.PreCodegen.after.mir Normal file
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@ -0,0 +1,15 @@
// MIR for `roundtrip` after PreCodegen
fn roundtrip(_1: *const u8) -> *const u8 {
debug x => _1; // in scope 0 at $DIR/casts.rs:+0:18: +0:19
let mut _0: *const u8; // return place in scope 0 at $DIR/casts.rs:+0:35: +0:44
let mut _2: *mut u8; // in scope 0 at $DIR/casts.rs:+1:5: +1:17
bb0: {
StorageLive(_2); // scope 0 at $DIR/casts.rs:+1:5: +1:17
_2 = _1 as *mut u8 (PtrToPtr); // scope 0 at $DIR/casts.rs:+1:5: +1:17
_0 = move _2 as *const u8 (Pointer(MutToConstPointer)); // scope 0 at $DIR/casts.rs:+1:5: +1:17
StorageDead(_2); // scope 0 at $DIR/casts.rs:+1:16: +1:17
return; // scope 0 at $DIR/casts.rs:+2:2: +2:2
}
}

17
tests/mir-opt/casts.rs Normal file
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@ -0,0 +1,17 @@
#![crate_type = "lib"]
// EMIT_MIR casts.redundant.InstCombine.diff
// EMIT_MIR casts.redundant.PreCodegen.after.mir
pub fn redundant<'a, 'b: 'a>(x: *const &'a u8) -> *const &'a u8 {
generic_cast::<&'a u8, &'b u8>(x) as *const &'a u8
}
#[inline]
fn generic_cast<T, U>(x: *const T) -> *const U {
x as *const U
}
// EMIT_MIR casts.roundtrip.PreCodegen.after.mir
pub fn roundtrip(x: *const u8) -> *const u8 {
x as *mut u8 as *const u8
}