[ConstantFold] Fix a crash when folding a GEP that has vector index

LLVM crashes when factoring out an out-of-bound index into preceding dimension
and the preceding dimension uses vector index.  Simply bail out now when this
case happens.

Differential Revision: https://reviews.llvm.org/D38677

llvm-svn: 316824
diff --git a/llvm/lib/IR/ConstantFold.cpp b/llvm/lib/IR/ConstantFold.cpp
index 044cc1f..c826f75 100644
--- a/llvm/lib/IR/ConstantFold.cpp
+++ b/llvm/lib/IR/ConstantFold.cpp
@@ -2219,6 +2219,9 @@
       Unknown = true;
       continue;
     }
+    if (!isa<ConstantInt>(Idxs[i - 1]))
+      // FIXME: add the support of cosntant vector index.
+      continue;
     if (InRangeIndex && i == *InRangeIndex + 1) {
       // If an index is marked inrange, we cannot apply this canonicalization to
       // the following index, as that will cause the inrange index to point to