[llvm] cb2cb2d - [InstCombine] Avoid deleting volatile memcpys.

[Patrick Walton via llvm-commits]

Author: Patrick Walton
Date: 2022-10-30T02:40:16-07:00
New Revision: cb2cb2d201811d95d4f35337817faea05654d8f0

URL: https://github.com/llvm/llvm-project/commit/cb2cb2d201811d95d4f35337817faea05654d8f0
DIFF: https://github.com/llvm/llvm-project/commit/cb2cb2d201811d95d4f35337817faea05654d8f0.diff

LOG: [InstCombine] Avoid deleting volatile memcpys.

InstCombine can replace memcpy to an alloca with a pointer directly to the
source in certain cases. Unfortunately, it also did so for volatile memcpys.
This patch makes it stop doing that.

This was discovered in D136822.

Differential Revision: https://reviews.llvm.org/D137031

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
    llvm/test/Transforms/InstCombine/memcpy-from-global.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index a1f29cb69efc0..23f6207a6b584 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -111,12 +111,14 @@ isOnlyCopiedFromConstantMemory(AAResults *AA,
       if (!MI)
         return false;
 
+      // If the transfer is volatile, reject it.
+      if (MI->isVolatile())
+        return false;
+
       // If the transfer is using the alloca as a source of the transfer, then
       // ignore it since it is a load (unless the transfer is volatile).
-      if (U.getOperandNo() == 1) {
-        if (MI->isVolatile()) return false;
+      if (U.getOperandNo() == 1)
         continue;
-      }
 
       // If we already have seen a copy, reject the second one.
       if (TheCopy) return false;

diff  --git a/llvm/test/Transforms/InstCombine/memcpy-from-global.ll b/llvm/test/Transforms/InstCombine/memcpy-from-global.ll
index 67fb0596e1a9e..a0cd39b233eed 100644
--- a/llvm/test/Transforms/InstCombine/memcpy-from-global.ll
+++ b/llvm/test/Transforms/InstCombine/memcpy-from-global.ll
@@ -366,10 +366,12 @@ define void @memcpy_from_just_readonly(ptr readonly align 8 dereferenceable(124)
   ret void
 }
 
-; FIXME: Test that we incorrectly elide a volatile memcpy.
+; Test that we don't elide a volatile memcpy.
 define void @volatile_memcpy() {
 ; CHECK-LABEL: @volatile_memcpy(
-; CHECK-NEXT:    call void @bar(ptr nonnull @H) #[[ATTR3]]
+; CHECK-NEXT:    [[A:%.*]] = alloca [[U:%.*]], align 16
+; CHECK-NEXT:    call void @llvm.memcpy.p0.p0.i64(ptr align 4 [[A]], ptr align 4 @H, i64 20, i1 true)
+; CHECK-NEXT:    call void @bar(ptr nonnull [[A]]) #[[ATTR3]]
 ; CHECK-NEXT:    ret void
 ;
   %A = alloca %U, align 16