[PATCH] D122911: [MemCpyOpt] Work around PR54682

[Nikita Popov via Phabricator via llvm-commits]

This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
Closed by commit rGa5c3b5748c11: [MemCpyOpt] Work around PR54682 (authored by nikic).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D122911/new/

https://reviews.llvm.org/D122911

Files:
  llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
  llvm/test/Transforms/MemCpyOpt/pr54682.ll


Index: llvm/test/Transforms/MemCpyOpt/pr54682.ll
===================================================================
--- llvm/test/Transforms/MemCpyOpt/pr54682.ll
+++ llvm/test/Transforms/MemCpyOpt/pr54682.ll
@@ -1,7 +1,8 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt -S -memcpyopt < %s | FileCheck %s
 
-; FIXME: This currently gets miscompiled.
+; The memcpy here is *not* dead, because it reads memory written in a previous
+; loop iteration.
 
 define void @test(i1 %c, i8* nocapture noundef readonly %path, i8* noundef writeonly %name) {
 ; CHECK-LABEL: @test(
@@ -17,6 +18,7 @@
 ; CHECK:       exit:
 ; CHECK-NEXT:    [[TMP_IV_1:%.*]] = getelementptr inbounds i8, i8* [[TMP_IV]], i64 1
 ; CHECK-NEXT:    [[LEN:%.*]] = sub nsw i64 259, [[IV]]
+; CHECK-NEXT:    call void @llvm.memcpy.p0i8.p0i8.i64(i8* align 1 [[NAME:%.*]], i8* nonnull align 1 [[TMP_IV_1]], i64 [[LEN]], i1 false)
 ; CHECK-NEXT:    ret void
 ;
 entry:
Index: llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -1427,7 +1427,8 @@
       }
 
   MemoryUseOrDef *MA = MSSA->getMemoryAccess(M);
-  MemoryAccess *AnyClobber = MSSA->getWalker()->getClobberingMemoryAccess(MA);
+  // FIXME: Not using getClobberingMemoryAccess() here due to PR54682.
+  MemoryAccess *AnyClobber = MA->getDefiningAccess();
   MemoryLocation DestLoc = MemoryLocation::getForDest(M);
   const MemoryAccess *DestClobber =
       MSSA->getWalker()->getClobberingMemoryAccess(AnyClobber, DestLoc);


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