[llvm] 4fbde1e - Fix MemorySSAUpdater::insertDef for dead code

[Artur Pilipenko via llvm-commits]

Author: Artur Pilipenko
Date: 2022-03-31T16:32:35-07:00
New Revision: 4fbde1ef40e6fa550b428b20a085a90d1fdfb071

URL: https://github.com/llvm/llvm-project/commit/4fbde1ef40e6fa550b428b20a085a90d1fdfb071
DIFF: https://github.com/llvm/llvm-project/commit/4fbde1ef40e6fa550b428b20a085a90d1fdfb071.diff

LOG: Fix MemorySSAUpdater::insertDef for dead code

Fix for https://github.com/llvm/llvm-project/issues/51257.

Differential Revision: https://reviews.llvm.org/D122601

Added: 
    llvm/test/Transforms/GVN/mssa-update-dead-def.ll

Modified: 
    llvm/lib/Analysis/MemorySSAUpdater.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/MemorySSAUpdater.cpp b/llvm/lib/Analysis/MemorySSAUpdater.cpp
index 4e94bc2b9e2d5..eb75118210b9a 100644
--- a/llvm/lib/Analysis/MemorySSAUpdater.cpp
+++ b/llvm/lib/Analysis/MemorySSAUpdater.cpp
@@ -305,6 +305,12 @@ static void setMemoryPhiValueForBlock(MemoryPhi *MP, const BasicBlock *BB,
 // point to the correct new defs, to ensure we only have one variable, and no
 // disconnected stores.
 void MemorySSAUpdater::insertDef(MemoryDef *MD, bool RenameUses) {
+  // Don't bother updating dead code.
+  if (!MSSA->DT->isReachableFromEntry(MD->getBlock())) {
+    MD->setDefiningAccess(MSSA->getLiveOnEntryDef());
+    return;
+  }
+
   VisitedBlocks.clear();
   InsertedPHIs.clear();
 
@@ -422,10 +428,10 @@ void MemorySSAUpdater::insertDef(MemoryDef *MD, bool RenameUses) {
   if (NewPhiSize)
     tryRemoveTrivialPhis(ArrayRef<WeakVH>(&InsertedPHIs[NewPhiIndex], NewPhiSize));
 
-  // Now that all fixups are done, rename all uses if we are asked. Skip
-  // renaming for defs in unreachable blocks.
+  // Now that all fixups are done, rename all uses if we are asked. The defs are
+  // guaranteed to be in reachable code due to the check at the method entry.
   BasicBlock *StartBlock = MD->getBlock();
-  if (RenameUses && MSSA->getDomTree().getNode(StartBlock)) {
+  if (RenameUses) {
     SmallPtrSet<BasicBlock *, 16> Visited;
     // We are guaranteed there is a def in the block, because we just got it
     // handed to us in this function.

diff  --git a/llvm/test/Transforms/GVN/mssa-update-dead-def.ll b/llvm/test/Transforms/GVN/mssa-update-dead-def.ll
new file mode 100644
index 0000000000000..db7a4a3a30c4f
--- /dev/null
+++ b/llvm/test/Transforms/GVN/mssa-update-dead-def.ll
@@ -0,0 +1,33 @@
+; RUN: opt -passes='require<memoryssa>,gvn' -verify-memoryssa -S %s | FileCheck %s
+
+; This is a regression test for a bug in MemorySSA updater.
+; Make sure that we don't crash and end up with a valid MemorySSA.
+
+; CHECK: @test()
+define void @test() personality i32* ()* null {
+  invoke void @bar()
+          to label %bar.normal unwind label %exceptional
+
+bar.normal:
+  ret void
+
+dead.block:
+  br label %baz.invoke
+
+baz.invoke:
+  invoke void @baz()
+          to label %baz.normal unwind label %exceptional
+
+baz.normal:
+  ret void
+
+exceptional:
+  %tmp9 = landingpad { i8*, i32 }
+          cleanup
+  call void @foo()
+  ret void
+}
+
+declare void @foo()
+declare void @bar()
+declare void @baz()