[ValueTracking] Fix crash in GetPointerBaseWithConstantOffset()

Summary:
While walking defs of pointer operands we were assuming that the pointer
size would remain constant.  This is not true, because addresspacecast
instructions may cast the pointer to an address space with a different
pointer width.

This partial reverts r282612, which was a more conservative solution
to this problem.

Reviewers: reames, sanjoy, apilipenko

Subscribers: wdng, llvm-commits

Differential Revision: https://reviews.llvm.org/D24772

llvm-svn: 283557

1 files changed, 10 insertions, 9 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 64a900d2960..6a4aaf1727a 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -2855,21 +2855,22 @@ Value *llvm::GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
       break;
 
     if (GEPOperator *GEP = dyn_cast<GEPOperator>(Ptr)) {
-      APInt GEPOffset(BitWidth, 0);
+      // If one of the values we have visited is an addrspacecast, then
+      // the pointer type of this GEP may be different from the type
+      // of the Ptr parameter which was passed to this function.  This
+      // means when we construct GEPOffset, we need to use the size
+      // of GEP's pointer type rather than the size of the original
+      // pointer type.
+      APInt GEPOffset(DL.getPointerTypeSizeInBits(Ptr->getType()), 0);
       if (!GEP->accumulateConstantOffset(DL, GEPOffset))
         break;
 
-      ByteOffset += GEPOffset;
+      ByteOffset += GEPOffset.getSExtValue();
 
       Ptr = GEP->getPointerOperand();
-    } else if (Operator::getOpcode(Ptr) == Instruction::BitCast) {
+    } else if (Operator::getOpcode(Ptr) == Instruction::BitCast ||
+               Operator::getOpcode(Ptr) == Instruction::AddrSpaceCast) {
       Ptr = cast<Operator>(Ptr)->getOperand(0);
-    } else if (AddrSpaceCastInst *ASCI = dyn_cast<AddrSpaceCastInst>(Ptr)) {
-      Value *SourcePtr = ASCI->getPointerOperand();
-      // Don't look through addrspace cast which changes pointer size
-      if (BitWidth != DL.getPointerTypeSizeInBits(SourcePtr->getType()))
-        break;
-      Ptr = SourcePtr;
     } else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(Ptr)) {
       if (GA->isInterposable())
         break;