[Evaluator] Bitcast result of pointer stripping

Trying to evaluate a GEP would assert with
  "Ty == cast<PointerType>(C->getType()->getScalarType())->getElementType()"
because the type of the pointer we would evaluate the GEP argument to
would be a different type than the GEP was expecting. We should treat
pointer stripping as a bitcast.

The test adds a redundant GEP that would crash due to type mismatch.

Reviewed By: rnk

Differential Revision: https://reviews.llvm.org/D100970

llvm/lib/Transforms/Utils/Evaluator.cpp

@@ -566,6 +566,7 @@ bool Evaluator::EvaluateBlock(BasicBlock::iterator CurInst, BasicBlock *&NextBB,
                        << "Stripped pointer casts for alias analysis for "
                           "intrinsic call.\n");
             StrippedPointerCastsForAliasAnalysis = true;
+            InstResult = ConstantExpr::getBitCast(InstResult, II->getType());
           } else {
             LLVM_DEBUG(dbgs() << "Unknown intrinsic. Cannot evaluate.\n");
             return false;

llvm/test/Transforms/GlobalOpt/invariant.group.ll

@@ -32,9 +32,10 @@ enter:
 
   %0 = bitcast i32* %valptr to i8*
   %barr = call i8* @llvm.launder.invariant.group(i8* %0)
-  %1 = bitcast i8* %barr to i32*
+  %1 = getelementptr i8, i8* %barr, i32 0
+  %2 = bitcast i8* %1 to i32*
 
-  %val2 = load i32, i32* %1
+  %val2 = load i32, i32* %2
   store i32 %val2, i32* @tmp2
   ret void
 }