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Auto merge of #78195 - tmiasko:instcombine, r=jonas-schievink

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Disable "optimization to avoid load of address" in InstCombine

The transformation is incorrect #78192. Disable it.
This commit is contained in:
bors 2020-10-21 17:44:48 +00:00
commit 1d2726726f
4 changed files with 8 additions and 3 deletions
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5
compiler/rustc_mir/src/transform/instcombine.rs
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@ -119,6 +119,11 @@ impl OptimizationFinder<'b, 'tcx> {
}
fn find_deref_of_address(&mut self, rvalue: &Rvalue<'tcx>, location: Location) -> Option<()> {
// FIXME(#78192): This optimization can result in unsoundness.
if !self.tcx.sess.opts.debugging_opts.unsound_mir_opts {
return None;
}
// Look for the sequence
//
// _2 = &_1;

2
src/test/mir-opt/const_prop/ref_deref.main.ConstProp.diff
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@ -19,7 +19,7 @@
// + span: $DIR/ref_deref.rs:5:6: 5:10
// + literal: Const { ty: &i32, val: Unevaluated(WithOptConstParam { did: DefId(0:3 ~ ref_deref[317d]::main), const_param_did: None }, [], Some(promoted[0])) }
_2 = _4; // scope 0 at $DIR/ref_deref.rs:5:6: 5:10
- _1 = (*_4); // scope 0 at $DIR/ref_deref.rs:5:5: 5:10
- _1 = (*_2); // scope 0 at $DIR/ref_deref.rs:5:5: 5:10
+ _1 = const 4_i32; // scope 0 at $DIR/ref_deref.rs:5:5: 5:10
StorageDead(_2); // scope 0 at $DIR/ref_deref.rs:5:10: 5:11
StorageDead(_1); // scope 0 at $DIR/ref_deref.rs:5:10: 5:11

2
src/test/mir-opt/const_prop/ref_deref_project.main.ConstProp.diff
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@ -19,7 +19,7 @@
// + span: $DIR/ref_deref_project.rs:5:6: 5:17
// + literal: Const { ty: &(i32, i32), val: Unevaluated(WithOptConstParam { did: DefId(0:3 ~ ref_deref_project[317d]::main), const_param_did: None }, [], Some(promoted[0])) }
_2 = &((*_4).1: i32); // scope 0 at $DIR/ref_deref_project.rs:5:6: 5:17
_1 = ((*_4).1: i32); // scope 0 at $DIR/ref_deref_project.rs:5:5: 5:17
_1 = (*_2); // scope 0 at $DIR/ref_deref_project.rs:5:5: 5:17
StorageDead(_2); // scope 0 at $DIR/ref_deref_project.rs:5:17: 5:18
StorageDead(_1); // scope 0 at $DIR/ref_deref_project.rs:5:17: 5:18
_0 = const (); // scope 0 at $DIR/ref_deref_project.rs:4:11: 6:2

2
src/test/mir-opt/inst_combine_deref.rs
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@ -1,4 +1,4 @@
// compile-flags: -O
// compile-flags: -O -Zunsound-mir-opts
// EMIT_MIR inst_combine_deref.simple_opt.InstCombine.diff
fn simple_opt() -> u64 {
let x = 5;