Fix a use-after-RAUW bug in large GEP splitting

Summary:
Large GEP splitting, introduced in rL332015, uses a `DenseMap<AssertingVH<Value>, ...>`. This causes an assertion to fail (in debug builds) or undefined behaviour to occur (in release builds) when a value is RAUWed.

This manifested itself in the 7zip benchmark from the llvm test suite built on ARM with `-fstrict-vtable-pointers` enabled while RAUWing invariant group launders and splits in CodeGenPrepare.

This patch merges the large offsets of the argument and the result of an invariant.group strip/launder intrinsic before RAUWing.

Reviewers: Prazek, javed.absar, haicheng, efriedma

Reviewed By: Prazek, efriedma

Subscribers: kristof.beyls, hiraditya, llvm-commits

Differential Revision: https://reviews.llvm.org/D51936

llvm-svn: 344802

1 files changed, 14 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/CodeGenPrepare.cpp b/llvm/lib/CodeGen/CodeGenPrepare.cpp
index dfbfae8..fa5cc4d 100644
--- a/llvm/lib/CodeGen/CodeGenPrepare.cpp
+++ b/llvm/lib/CodeGen/CodeGenPrepare.cpp
@@ -1721,11 +1721,22 @@ bool CodeGenPrepare::optimizeCallInst(CallInst *CI, bool &ModifiedDT) {
       return true;
     }
     case Intrinsic::launder_invariant_group:
-    case Intrinsic::strip_invariant_group:
-      II->replaceAllUsesWith(II->getArgOperand(0));
+    case Intrinsic::strip_invariant_group: {
+      Value *ArgVal = II->getArgOperand(0);
+      auto it = LargeOffsetGEPMap.find(II);
+      if (it != LargeOffsetGEPMap.end()) {
+          // Merge entries in LargeOffsetGEPMap to reflect the RAUW.
+          // Make sure not to have to deal with iterator invalidation
+          // after possibly adding ArgVal to LargeOffsetGEPMap.
+          auto GEPs = std::move(it->second);
+          LargeOffsetGEPMap[ArgVal].append(GEPs.begin(), GEPs.end());
+          LargeOffsetGEPMap.erase(II);
+      }
+
+      II->replaceAllUsesWith(ArgVal);
       II->eraseFromParent();
       return true;
-
+    }
     case Intrinsic::cttz:
     case Intrinsic::ctlz:
       // If counting zeros is expensive, try to avoid it.