[llvm] r325971 - [MemorySSA] Fix a cache invalidation bug with removed accesses

[George Burgess IV via llvm-commits]

Author: gbiv
Date: Fri Feb 23 15:07:18 2018
New Revision: 325971

URL: http://llvm.org/viewvc/llvm-project?rev=325971&view=rev
Log:
[MemorySSA] Fix a cache invalidation bug with removed accesses

I suspect there's a deeper issue here, but we probably shouldn't be
using INVALID_MEMORYSSA_ID as liveOnEntry's ID anyway.

Modified:
    llvm/trunk/include/llvm/Analysis/MemorySSA.h
    llvm/trunk/lib/Analysis/MemorySSA.cpp
    llvm/trunk/unittests/Analysis/MemorySSA.cpp

Modified: llvm/trunk/include/llvm/Analysis/MemorySSA.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Analysis/MemorySSA.h?rev=325971&r1=325970&r2=325971&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Analysis/MemorySSA.h (original)
+++ llvm/trunk/include/llvm/Analysis/MemorySSA.h Fri Feb 23 15:07:18 2018
@@ -118,10 +118,10 @@ struct DefsOnlyTag {};
 
 } // end namespace MSSAHelpers
 
-enum {
+enum : unsigned {
   // Used to signify what the default invalid ID is for MemoryAccess's
   // getID()
-  INVALID_MEMORYACCESS_ID = 0
+  INVALID_MEMORYACCESS_ID = -1U
 };
 
 template <class T> class memoryaccess_def_iterator_base;

Modified: llvm/trunk/lib/Analysis/MemorySSA.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/MemorySSA.cpp?rev=325971&r1=325970&r2=325971&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/MemorySSA.cpp (original)
+++ llvm/trunk/lib/Analysis/MemorySSA.cpp Fri Feb 23 15:07:18 2018
@@ -1033,7 +1033,7 @@ void MemorySSA::markUnreachableAsLiveOnE
 
 MemorySSA::MemorySSA(Function &Func, AliasAnalysis *AA, DominatorTree *DT)
     : AA(AA), DT(DT), F(Func), LiveOnEntryDef(nullptr), Walker(nullptr),
-      NextID(INVALID_MEMORYACCESS_ID) {
+      NextID(0) {
   buildMemorySSA();
 }
 

Modified: llvm/trunk/unittests/Analysis/MemorySSA.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/Analysis/MemorySSA.cpp?rev=325971&r1=325970&r2=325971&view=diff
==============================================================================
--- llvm/trunk/unittests/Analysis/MemorySSA.cpp (original)
+++ llvm/trunk/unittests/Analysis/MemorySSA.cpp Fri Feb 23 15:07:18 2018
@@ -909,3 +909,45 @@ TEST_F(MemorySSATest, Irreducible) {
   Updater.insertUse(LoadAccess);
   MSSA.verifyMemorySSA();
 }
+
+TEST_F(MemorySSATest, MoveToBeforeLiveOnEntryInvalidatesCache) {
+  // Create:
+  //   %1 = alloca i8
+  //   ; 1 = MemoryDef(liveOnEntry)
+  //   store i8 0, i8* %1
+  //   ; 2 = MemoryDef(1)
+  //   store i8 0, i8* %1
+  //
+  // ...And be sure that MSSA's caching doesn't give us `1` for the clobber of
+  // `2` after `1` is removed.
+  IRBuilder<> B(C);
+  F = Function::Create(
+      FunctionType::get(B.getVoidTy(), {B.getInt8PtrTy()}, false),
+      GlobalValue::ExternalLinkage, "F", &M);
+
+  BasicBlock *Entry = BasicBlock::Create(C, "if", F);
+  B.SetInsertPoint(Entry);
+
+  Value *A = B.CreateAlloca(B.getInt8Ty());
+  StoreInst *StoreA = B.CreateStore(B.getInt8(0), A);
+  StoreInst *StoreB = B.CreateStore(B.getInt8(0), A);
+
+  setupAnalyses();
+
+  MemorySSA &MSSA = *Analyses->MSSA;
+
+  auto *DefA = cast<MemoryDef>(MSSA.getMemoryAccess(StoreA));
+  auto *DefB = cast<MemoryDef>(MSSA.getMemoryAccess(StoreB));
+
+  MemoryAccess *BClobber = MSSA.getWalker()->getClobberingMemoryAccess(DefB);
+  ASSERT_EQ(DefA, BClobber);
+
+  MemorySSAUpdater(&MSSA).removeMemoryAccess(DefA);
+  StoreA->eraseFromParent();
+
+  EXPECT_EQ(DefB->getDefiningAccess(), MSSA.getLiveOnEntryDef());
+
+  EXPECT_EQ(MSSA.getWalker()->getClobberingMemoryAccess(DefB),
+            MSSA.getLiveOnEntryDef())
+      << "(DefA = " << DefA << ")";
+}