CastInst::castIsValid should return true if the dest type is the same as
Value's current type. The casting is trivial even for aggregate type.

llvm-svn: 172143
diff --git a/llvm/lib/IR/Instructions.cpp b/llvm/lib/IR/Instructions.cpp
index f2e9813..26398ce 100644
--- a/llvm/lib/IR/Instructions.cpp
+++ b/llvm/lib/IR/Instructions.cpp
@@ -2624,6 +2624,11 @@
 
   // Check for type sanity on the arguments
   Type *SrcTy = S->getType();
+
+  // If this is a cast to the same type then it's trivially true.
+  if (SrcTy == DstTy)
+    return true;
+
   if (!SrcTy->isFirstClassType() || !DstTy->isFirstClassType() ||
       SrcTy->isAggregateType() || DstTy->isAggregateType())
     return false;