[LICM] allow MemoryAccess creation failure

Author: dianqk

llvm/include/llvm/Analysis/MemorySSAUpdater.h

@@ -190,7 +190,8 @@ class MemorySSAUpdater {
   /// inaccessible and it *must* have removeMemoryAccess called on it.
   MemoryAccess *createMemoryAccessInBB(Instruction *I, MemoryAccess *Definition,
                                        const BasicBlock *BB,
-                                       MemorySSA::InsertionPlace Point);
+                                       MemorySSA::InsertionPlace Point,
+                                       bool CreationMustSucceed = true);
 
   /// Create a MemoryAccess in MemorySSA before an existing MemoryAccess.
   ///

llvm/lib/Analysis/MemorySSAUpdater.cpp

@@ -1403,9 +1403,11 @@ void MemorySSAUpdater::changeToUnreachable(const Instruction *I) {
 
 MemoryAccess *MemorySSAUpdater::createMemoryAccessInBB(
     Instruction *I, MemoryAccess *Definition, const BasicBlock *BB,
-    MemorySSA::InsertionPlace Point) {
-  MemoryUseOrDef *NewAccess = MSSA->createDefinedAccess(I, Definition);
-  MSSA->insertIntoListsForBlock(NewAccess, BB, Point);
+    MemorySSA::InsertionPlace Point, bool CreationMustSucceed) {
+  MemoryUseOrDef *NewAccess = MSSA->createDefinedAccess(
+      I, Definition, /*Template=*/nullptr, CreationMustSucceed);
+  if (NewAccess)
+    MSSA->insertIntoListsForBlock(NewAccess, BB, Point);
   return NewAccess;
 }
 

llvm/lib/Transforms/Scalar/LICM.cpp

@@ -1465,8 +1465,11 @@ static Instruction *cloneInstructionInExitBlock(
 
   if (MSSAU.getMemorySSA()->getMemoryAccess(&I)) {
     // Create a new MemoryAccess and let MemorySSA set its defining access.
+    // After running some passes, MemorySSA might be outdated, and the
+    // instruction `I` may have become a non-memory touching instruction.
     MemoryAccess *NewMemAcc = MSSAU.createMemoryAccessInBB(
-        New, nullptr, New->getParent(), MemorySSA::Beginning);
+        New, nullptr, New->getParent(), MemorySSA::Beginning,
+        /*CreationMustSucceed=*/false);
     if (NewMemAcc) {
       if (auto *MemDef = dyn_cast<MemoryDef>(NewMemAcc))
         MSSAU.insertDef(MemDef, /*RenameUses=*/true);

llvm/test/Transforms/SimpleLoopUnswitch/nontrivial-unswitch-pred-removed.ll renamed to llvm/test/Transforms/LICM/PR116813-memoryssa-outdated.ll

@@ -1,4 +1,8 @@
 ; RUN: opt -passes='loop-mssa(simple-loop-unswitch<nontrivial>),print<memoryssa>' -verify-memoryssa -disable-output -S < %s 2>&1 | FileCheck %s
+; RUN: opt -passes='loop-mssa(simple-loop-unswitch<nontrivial>,licm)' -verify-memoryssa -disable-output -S
+
+; Check that SimpleLoopUnswitch preserves the MemoryDef of `call i32 @bar()`.
+; Also, check that running LICM after SimpleLoopUnswitch does not result in a crash.
 
 ; CHECK: preds = %bb2{{$}}
 ; CHECK-NEXT: MemoryDef