[LoopVectorize] Don't crash on zero-sized types in isInductionPHI

isInductionPHI wants to calculate the stride based on the pointee size.
However, this is not possible when the pointee is zero sized.

This fixes PR23763.

llvm-svn: 239143
diff --git a/llvm/lib/Transforms/Utils/LoopUtils.cpp b/llvm/lib/Transforms/Utils/LoopUtils.cpp
index a5890c0..5f25e6b 100644
--- a/llvm/lib/Transforms/Utils/LoopUtils.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUtils.cpp
@@ -491,6 +491,9 @@
 
   const DataLayout &DL = Phi->getModule()->getDataLayout();
   int64_t Size = static_cast<int64_t>(DL.getTypeAllocSize(PointerElementType));
+  if (!Size)
+    return false;
+
   int64_t CVSize = CV->getSExtValue();
   if (CVSize % Size)
     return false;