[llvm] [DirectX] Address PR comments to #131221 (PR #131706)

[Justin Bogner via llvm-commits]

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@@ -61,47 +43,66 @@ static void fixI8TruncUseChain(Instruction &I,
         // Note: options here are sext or sextOrTrunc.
         // Since i8 isn't supported, we assume new values
         // will always have a higher bitness.
+        assert(NewBitWidth > Value.getBitWidth() &&
+               "Replacement's BitWidth should be larger than Current.");
         APInt NewValue = Value.sext(NewBitWidth);
         NewOperands.push_back(ConstantInt::get(InstrType, NewValue));
       } else {
         assert(!Op->getType()->isIntegerTy(8));
         NewOperands.push_back(Op);
       }
     }
-
-    Value *NewInst = nullptr;
-    if (auto *BO = dyn_cast<BinaryOperator>(&I)) {
-      NewInst =
-          Builder.CreateBinOp(BO->getOpcode(), NewOperands[0], NewOperands[1]);
-
-      if (auto *OBO = dyn_cast<OverflowingBinaryOperator>(&I)) {
-        if (OBO->hasNoSignedWrap())
-          cast<BinaryOperator>(NewInst)->setHasNoSignedWrap();
-        if (OBO->hasNoUnsignedWrap())
-          cast<BinaryOperator>(NewInst)->setHasNoUnsignedWrap();
-      }
-    } else if (Cmp) {
-      NewInst = Builder.CreateCmp(Cmp->getPredicate(), NewOperands[0],
-                                  NewOperands[1]);
-      Cmp->replaceAllUsesWith(NewInst);
+  };
+  IRBuilder<> Builder(&I);
+  if (auto *Trunc = dyn_cast<TruncInst>(&I)) {
+    if (Trunc->getDestTy()->isIntegerTy(8)) {
+      ReplacedValues[Trunc] = Trunc->getOperand(0);
+      ToRemove.push_back(Trunc);
----------------
bogner wrote:

Would make sense to return here - none of the following code is possible if the instruction is a trunc.

https://github.com/llvm/llvm-project/pull/131706