[Attributor][Fix] Use right type to replace expressions

[jdoerfert]

Summary

This should be obsolete once the functionality in D66967 is integrated.

[uenoku]

LGTM.

llvm/lib/Transforms/IPO/Attributor.cpp

if (auto *UniqueRVArg = dyn_cast<Argument>(UniqueRV.getValue())) {
     getIRPosition() = IRPosition::argument(*UniqueRVArg);
     Changed = IRAttribute::manifest(A);
   } else if (auto *RVC = dyn_cast<Constant>(UniqueRV.getValue())) {
     // We can replace the returned value with the unique returned constant.
     Value &AnchorValue = getAnchorValue();
     if (Function *F = dyn_cast<Function>(&AnchorValue)) {
       for (const Use &U : F->uses())
         if (CallBase *CB = dyn_cast<CallBase>(U.getUser()))
-          if (CB->isCallee(&U))
-            Changed = ReplaceCallSiteUsersWith(*CB, *RVC) | Changed;
+          if (CB->isCallee(&U)) {
+            Constant *RVCCast =
+                ConstantExpr::getTruncOrBitCast(RVC, CB->getType());
+            Changed = ReplaceCallSiteUsersWith(*CB, *RVCCast) | Changed;
+          }
     } else {
       assert(isa<CallBase>(AnchorValue) &&
              "Expcected a function or call base anchor!");
-      Changed = ReplaceCallSiteUsersWith(cast<CallBase>(AnchorValue), *RVC);
+      Constant *RVCCast =
+          ConstantExpr::getTruncOrBitCast(RVC, AnchorValue.getType());
+      Changed = ReplaceCallSiteUsersWith(cast<CallBase>(AnchorValue), *RVCCast);
     }
     if (Changed == ChangeStatus::CHANGED)
       STATS_DECLTRACK(UniqueConstantReturnValue, FunctionReturn,
                       "Number of function returns replaced by constant return");
   }
 
   return Changed;
 }

llvm/test/Transforms/FunctionAttrs/arg_returned.ll

 ; CHECK:  %add2 = add i32 %add1, %c2
 ; CHECK:  %add3 = add i32 %add2, %c3
   %add1 = add i32 %c0, %c1
   %add2 = add i32 %add1, %c2
   %add3 = add i32 %add2, %c4
   ret i32 %add3
 }
 
+@G = external global i8
+define i32* @ret_const() {
+  %bc = bitcast i8* @G to i32*
+  ret i32* %bc
+}
+define i32* @use_const() {
+  %c = call i32* @ret_const()
+  ; CHECK: ret i32* bitcast (i8* @G to i32*)
+  ret i32* %c
+}
+
 attributes #0 = { noinline nounwind uwtable }
 
 ; BOTH-NOT: attributes #
 ; BOTH-DAG: attributes #{{[0-9]*}} = { nofree noinline norecurse nosync nounwind readnone uwtable willreturn }
 ; BOTH-DAG: attributes #{{[0-9]*}} = { nofree noinline nosync nounwind readnone uwtable }
 ; BOTH-DAG: attributes #{{[0-9]*}} = { nofree noinline noreturn nosync nounwind readonly uwtable }
 ; BOTH-DAG: attributes #{{[0-9]*}} = { noinline nounwind uwtable }
 ; BOTH-DAG: attributes #{{[0-9]*}} = { noreturn }
 ; BOTH-DAG: attributes #{{[0-9]*}} = { nofree nosync willreturn }
 ; BOTH-DAG: attributes #{{[0-9]*}} = { nofree nosync }
 ; BOTH-DAG: attributes #{{[0-9]*}} = { nofree noreturn nosync }
 ; BOTH-NOT: attributes #