[ValueTracking] Fix a misuse of APInt in GetPointerBaseWithConstantOffset

GetPointerBaseWithConstantOffset include this code, where ByteOffset
and GEPOffset are both of type llvm::APInt :

  ByteOffset += GEPOffset.getSExtValue();

The problem with this line is that getSExtValue() returns an int64_t, but
the += matches an overload for uint64_t. The problem is that the resulting
APInt is no longer considered to be signed. That in turn causes assertion
failures later on if the relevant pointer type is > 64 bits in width and
the GEPOffset was negative.

Changing it to

  ByteOffset += GEPOffset.sextOrTrunc(ByteOffset.getBitWidth());

resolves the issue and explicitly performs the sign-extending
or truncation. Additionally, instead of asserting later if the result
is > 64 bits, it breaks out of the loop in that case.

See also
 https://reviews.llvm.org/D24729
 https://reviews.llvm.org/D24772

This commit must be merged after D38662 in order for the test to pass.

Patch by Michael Ferguson <mpfergu@gmail.com>.

Reviewers: reames, sanjoy, hfinkel

Reviewed By: hfinkel

Differential Revision: https://reviews.llvm.org/D38501

llvm-svn: 350395

1 files changed, 8 insertions, 1 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index efbab47406c..3c4cf1d88f9 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -3389,7 +3389,14 @@ Value *llvm::GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
       if (!GEP->accumulateConstantOffset(DL, GEPOffset))
         break;
 
-      ByteOffset += GEPOffset.getSExtValue();
+      APInt OrigByteOffset(ByteOffset);
+      ByteOffset += GEPOffset.sextOrTrunc(ByteOffset.getBitWidth());
+      if (ByteOffset.getMinSignedBits() > 64) {
+        // Stop traversal if the pointer offset wouldn't fit into int64_t
+        // (this should be removed if Offset is updated to an APInt)
+        ByteOffset = OrigByteOffset;
+        break;
+      }
 
       Ptr = GEP->getPointerOperand();
     } else if (Operator::getOpcode(Ptr) == Instruction::BitCast ||