[TypePromotion] Don't mutate the result type of SwitchInst.

SwitchInst should have a void result type.

Add a check to the verifier to catch this error.

Reviewed By: samparker

Differential Revision: https://reviews.llvm.org/D108084

Author: topperc

llvm/lib/CodeGen/TypePromotion.cpp

@@ -539,8 +539,8 @@ void IRPromoter::PromoteTree() {
         I->setOperand(i, UndefValue::get(ExtTy));
     }
 
-    // Mutate the result type, unless this is an icmp.
-    if (!isa<ICmpInst>(I)) {
+    // Mutate the result type, unless this is an icmp or switch.
+    if (!isa<ICmpInst>(I) && !isa<SwitchInst>(I)) {
       I->mutateType(ExtTy);
       Promoted.insert(I);
     }

llvm/lib/IR/Verifier.cpp

@@ -2691,6 +2691,7 @@ void Verifier::visitReturnInst(ReturnInst &RI) {
 }
 
 void Verifier::visitSwitchInst(SwitchInst &SI) {
+  Assert(SI.getType()->isVoidTy(), "Switch must have void result type!", &SI);
   // Check to make sure that all of the constants in the switch instruction
   // have the same type as the switched-on value.
   Type *SwitchTy = SI.getCondition()->getType();