[Evaluator] Bitcast result of pointer stripping

[aeubanks]

Summary

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.

[rnk]

lgtm

llvm/lib/Transforms/Utils/Evaluator.cpp

if (StoreInst *SI = dyn_cast<StoreInst>(CurInst)) {
           if (Stripped != &*CurInst) {
             InstResult = getVal(Stripped);
           }
           if (InstResult) {
             LLVM_DEBUG(dbgs()
                        << "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;
           }
         }
       }
 
       if (!InstResult) {

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

enter:
   %valptr = alloca i32
 
   %val = call i32 @TheAnswerToLifeTheUniverseAndEverything()
   store i32 %val, i32* @tmp
   store i32 %val, i32* %valptr
 
   %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
 }
 
 ; We can't step through launder.invariant.group here, because that would change
 ; this load in @usage_of_globals()
 ; %val = load i32, i32* %ptrVal, !invariant.group !0
 ; into