update per copilot suggestion

Author: wenju-he

llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp

@@ -1529,13 +1529,13 @@ Instruction *InstCombinerImpl::visitSExt(SExtInst &Sext) {
 
   // Try to extend the entire expression tree to the wide destination type.
   bool shouldExtendExpression = true;
-  Value *X = nullptr;
+  Value *Trunc = nullptr;
   // Do not extend expression in the trunc + sext pattern when destination type
   // is narrower than original (pre-trunc) type: modern architectures typically
   // provide efficient sign-extend instruction, so preserving the sext is
   // preferable here.
-  if (match(Src, m_Trunc(m_Value(X))))
-    if (X->getType()->getScalarSizeInBits() > DestBitSize)
+  if (match(Src, m_Trunc(m_Value(Trunc))))
+    if (Trunc->getType()->getScalarSizeInBits() > DestBitSize)
       shouldExtendExpression = false;
   if (shouldExtendExpression && shouldChangeType(SrcTy, DestTy) &&
       canEvaluateSExtd(Src, DestTy)) {
@@ -1558,6 +1558,7 @@ Instruction *InstCombinerImpl::visitSExt(SExtInst &Sext) {
                                       ShAmt);
   }
 
+  Value *X = Trunc;
   if (X) {
     // If the input has more sign bits than bits truncated, then convert
     // directly to final type.