[llvm] a2bb731 - [InstCombine] Do not combine atomic and non-atomic loads

[Sanjay Patel via llvm-commits]

Author: Ricky Zhou
Date: 2022-01-30T09:28:56-05:00
New Revision: a2bb7313e62daa8aaa9b06fe57386ed7221a990a

URL: https://github.com/llvm/llvm-project/commit/a2bb7313e62daa8aaa9b06fe57386ed7221a990a
DIFF: https://github.com/llvm/llvm-project/commit/a2bb7313e62daa8aaa9b06fe57386ed7221a990a.diff

LOG: [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

Added: 
    

Modified: 
    llvm/test/Transforms/InstCombine/phi.ll

Removed: 
    


################################################################################
diff  --git a/llvm/test/Transforms/InstCombine/phi.ll b/llvm/test/Transforms/InstCombine/phi.ll
index b9f54862b8947..51d5baf0ef53d 100644
--- a/llvm/test/Transforms/InstCombine/phi.ll
+++ b/llvm/test/Transforms/InstCombine/phi.ll
@@ -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:%.*]]