[ConstantFolding] Avoid assert when folding ptrtoint of vectorized GEP

Summary:
Got asserts in llvm::CastInst::getCastOpcode saying:
`DestBits == SrcBits && "Illegal cast to vector (wrong type or size)"' failed.

Problem seemed to be that llvm::ConstantFoldCastInstruction did
not handle ptrtoint cast of a getelementptr returning a vector
correctly. I assume such situations are quite rare, since the
GEP needs to be considered as a constant value (base pointer
being null).
The solution used here is to simply avoid the constant fold
of ptrtoint when the value is a vector. It is not supported,
and by bailing out we do not fail on assertions later on.

Reviewers: craig.topper, majnemer, davide, filcab, efriedma

Reviewed By: efriedma

Subscribers: efriedma, filcab, llvm-commits

Differential Revision: https://reviews.llvm.org/D38546

llvm-svn: 316430

1 files changed, 9 insertions, 0 deletions

diff --git a/llvm/lib/IR/ConstantFold.cpp b/llvm/lib/IR/ConstantFold.cpp
index 60dd20e4659..044cc1ff449 100644
--- a/llvm/lib/IR/ConstantFold.cpp
+++ b/llvm/lib/IR/ConstantFold.cpp
@@ -629,6 +629,15 @@ Constant *llvm::ConstantFoldCastInstruction(unsigned opc, Constant *V,
     if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
       if (CE->getOpcode() == Instruction::GetElementPtr &&
           CE->getOperand(0)->isNullValue()) {
+        // FIXME: Looks like getFoldedSizeOf(), getFoldedOffsetOf() and
+        // getFoldedAlignOf() don't handle the case when DestTy is a vector of
+        // pointers yet. We end up in asserts in CastInst::getCastOpcode (see
+        // test/Analysis/ConstantFolding/cast-vector.ll). I've only seen this
+        // happen in one "real" C-code test case, so it does not seem to be an
+        // important optimization to handle vectors here. For now, simply bail
+        // out.
+        if (DestTy->isVectorTy())
+          return nullptr;
         GEPOperator *GEPO = cast<GEPOperator>(CE);
         Type *Ty = GEPO->getSourceElementType();
         if (CE->getNumOperands() == 2) {