InstCombine: Fix an edge case where constant icmps could sneak into ConstantFoldInstOperands and crash.

Have to refactor the ConstantFolder interface one day to define bugs like this away. Fixes PR14131.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@166374 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/InstCombine/InstCombineSelect.cpp b/lib/Transforms/InstCombine/InstCombineSelect.cpp
index ecce242..a2d4c88 100644
--- a/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -333,6 +333,10 @@
 
     // All operands were constants, fold it.
     if (ConstOps.size() == I->getNumOperands()) {
+      if (CmpInst *C = dyn_cast<CmpInst>(I))
+        return ConstantFoldCompareInstOperands(C->getPredicate(), ConstOps[0],
+                                               ConstOps[1], TD, TLI);
+
       if (LoadInst *LI = dyn_cast<LoadInst>(I))
         if (!LI->isVolatile())
           return ConstantFoldLoadFromConstPtr(ConstOps[0], TD);