[TypePromotion] Refine fix sext/zext for promoted constant from D125294.

[craig.topper]

Summary

Reviewing the code again, I believe the sext is needed on the LHS
or RHS for ICmp and only on the RHS for Add/Sub.

Add an opcode check before checking the operand number.

[craig.topper]

Add test

[craig.topper]

I went ahead and pushed this to close out PR55627 which @regehr found. If we need to we can address any comments with a followup patch.

llvm/lib/CodeGen/TypePromotion.cpp

 //===----- TypePromotion.cpp ----------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
if (Sinks.count(I))
       continue;
 
     for (unsigned i = 0, e = I->getNumOperands(); i < e; ++i) {
       Value *Op = I->getOperand(i);
       if ((Op->getType() == ExtTy) || !isa<IntegerType>(Op->getType()))
         continue;
 
       if (auto *Const = dyn_cast<ConstantInt>(Op)) {
-        Constant *NewConst = (SafeWrap.contains(I) && i == 1)
+        // For ICmp, the constant can be on the LHS or RHS. For Add/Sub the
+        // constant we checked for sext is on the RHS.
+        Constant *NewConst = (SafeWrap.contains(I) &&
+                              (I->getOpcode() == Instruction::ICmp || i == 1))
                                  ? ConstantExpr::getSExt(Const, ExtTy)
                                  : ConstantExpr::getZExt(Const, ExtTy);
         I->setOperand(i, NewConst);
       } else if (isa<UndefValue>(Op))
         I->setOperand(i, ConstantInt::get(ExtTy, 0));
     }
 
     // Mutate the result type, unless this is an icmp or switch.