[InstCombine] Add check to avoid dependent optimization order, NFC

Since PR86428, foldPowiReassoc is called by both FMul and FDiv,
as the optimization of FDiv is placed after the FMul, so now
it is correct we don't add the checking of FDiv for powi(X, Y) / X.
But, we may add more matching scenarios later, so add the checking opcode
explicitly is easier to understand.

Author: vfdff

llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp

@@ -582,6 +582,9 @@ Instruction *InstCombinerImpl::foldPowiReassoc(BinaryOperator &I) {
   };
 
   Value *X, *Y, *Z;
+  unsigned Opcode = I.getOpcode();
+  assert((Opcode == Instruction::FMul || Opcode == Instruction::FDiv) &&
+         "Unexpected opcode");
 
   // powi(X, Y) * X --> powi(X, Y+1)
   // X * powi(X, Y) --> powi(X, Y+1)
@@ -596,7 +599,7 @@ Instruction *InstCombinerImpl::foldPowiReassoc(BinaryOperator &I) {
   // powi(x, y) * powi(x, z) -> powi(x, y + z)
   Value *Op0 = I.getOperand(0);
   Value *Op1 = I.getOperand(1);
-  if (I.isOnlyUserOfAnyOperand() &&
+  if (Opcode == Instruction::FMul && I.isOnlyUserOfAnyOperand() &&
       match(Op0, m_AllowReassoc(
                      m_Intrinsic<Intrinsic::powi>(m_Value(X), m_Value(Y)))) &&
       match(Op1, m_AllowReassoc(m_Intrinsic<Intrinsic::powi>(m_Specific(X),
@@ -608,7 +611,7 @@ Instruction *InstCombinerImpl::foldPowiReassoc(BinaryOperator &I) {
   // This is legal when (Y - 1) can't wraparound, in which case reassoc and nnan
   // are required.
   // TODO: Multi-use may be also better off creating Powi(x,y-1)
-  if (I.hasAllowReassoc() && I.hasNoNaNs() &&
+  if (Opcode == Instruction::FDiv && I.hasAllowReassoc() && I.hasNoNaNs() &&
       match(Op0, m_OneUse(m_AllowReassoc(m_Intrinsic<Intrinsic::powi>(
                      m_Specific(Op1), m_Value(Y))))) &&
       willNotOverflowSignedSub(Y, ConstantInt::get(Y->getType(), 1), I)) {