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[InstCombine] Do not combine atomic and non-atomic loads 

Before this change, InstCombine was willing to fold atomic and
non-atomic loads through a PHI node as long as the first PHI argument
is not an atomic load. The combined load would be non-atomic, which is
incorrect.

Fix this by only combining the loads in a PHI node when all of the
arguments are non-atomic loads.

Thanks to Eli Friedman for pointing out the bug at
https://github.com/llvm/llvm-project/issues/50777#issuecomment-981045342!

Fixes #50777

Differential Revision: https://reviews.llvm.org/D115113
This commit is contained in:
Ricky Zhou 2022-01-30 09:28:56 -05:00 committed by Sanjay Patel
parent de80b53d1a
commit a2bb7313e6
1 changed files with 25 additions and 0 deletions
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25
llvm/test/Transforms/InstCombine/phi.ll
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@ -547,6 +547,31 @@ bb2: ; preds = %bb1, %entry
ret i32 %res
}
; FIXME: Atomic and non-atomic loads should not be combined.
define i32 @PR51435(i32* %ptr, i32* %atomic_ptr, i1 %c) {
; CHECK-LABEL: @PR51435(
; CHECK: entry:
; CHECK-NEXT: br i1 %c, label %if, label %end
; CHECK: if:
; CHECK-NEXT: [[ATOMIC:%.*]] = load atomic i32, i32* %atomic_ptr acquire, align 4
; CHECK-NEXT: br label %end
; CHECK: end:
; CHECK-NEXT: [[COND_IN:%.*]] = phi i32* [ %ptr, %entry ], [ %atomic_ptr, %if ]
; CHECK-NEXT: [[COND:%.*]] = load i32, i32* [[COND_IN]], align 4
; CHECK-NEXT: ret i32 [[COND]]
entry:
%x = load i32, i32* %ptr, align 4
br i1 %c, label %if, label %end
if:
%y = load atomic i32, i32* %atomic_ptr acquire, align 4
br label %end
end:
%cond = phi i32 [ %x, %entry ], [ %y, %if ]
ret i32 %cond
}
define i1 @test18(i1 %cond) {
; CHECK-LABEL: @test18(
; CHECK-NEXT: br i1 [[COND:%.*]], label [[TRUE:%.*]], label [[FALSE:%.*]]