[MergeICmps] Do not perform the transformation if GEP is used outside of block

Summary:
This patch prevents MergeICmps to performn the transformation if the address operand GEP of the load instruction has a use outside of the load's parent block. Without this patch, compiler crashes with the given test case because the use of `%first.i` is still around when the basic block is erased from https://github.com/llvm-mirror/llvm/blob/master/lib/Transforms/Scalar/MergeICmps.cpp#L620. I think checking `isUsedOutsideOfBlock` with `GEP` is the original intention of the code, as the checking for `LoadI` is already performed in the same function.

This patch is incomplete though, as this makes the pass overly conservative and fails the test `tuple-four-int8.ll`. I believe what needs to be done is checking if GEP has a use outside of block that is not the part of "Comparisons" chain. Submit the patch as of now to prevent compiler crash.

Reviewers: courbet, trentxintong

Reviewed By: courbet

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D54089

llvm-svn: 346151

1 files changed, 1 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Scalar/MergeICmps.cpp b/llvm/lib/Transforms/Scalar/MergeICmps.cpp
index 3633485d5d5..69fd8b163a0 100644
--- a/llvm/lib/Transforms/Scalar/MergeICmps.cpp
+++ b/llvm/lib/Transforms/Scalar/MergeICmps.cpp
@@ -98,7 +98,7 @@ BCEAtom visitICmpLoadOperand(Value *const Val) {
     Value *const Addr = LoadI->getOperand(0);
     if (auto *const GEP = dyn_cast<GetElementPtrInst>(Addr)) {
       LLVM_DEBUG(dbgs() << "GEP\n");
-      if (LoadI->isUsedOutsideOfBlock(LoadI->getParent())) {
+      if (GEP->isUsedOutsideOfBlock(LoadI->getParent())) {
         LLVM_DEBUG(dbgs() << "used outside of block\n");
         return {};
       }