[llvm] [CostModel][AArch64] Make extractelement, with fmul user, free whenev… (PR #111479)

[Sushant Gokhale via llvm-commits]

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@@ -3145,12 +3153,16 @@ InstructionCost AArch64TTIImpl::getCFInstrCost(unsigned Opcode,
   return 0;
 }
 
-InstructionCost AArch64TTIImpl::getVectorInstrCostHelper(const Instruction *I,
-                                                         Type *Val,
-                                                         unsigned Index,
-                                                         bool HasRealUse) {
+InstructionCost AArch64TTIImpl::getVectorInstrCostHelper(
+    std::variant<const Instruction *, const unsigned> InstOrOpcode, Type *Val,
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sushgokh wrote:

You really cant merge the code for instruction and opcode, atleast for the patch, because the change wont be reflected in the cost-model tests.  
1. When `opcode!=null` , less information is available  and we bail out early in general. 
2. When `I!=null`, more analysis needs to be done.

I will keep seperate `instruction` and `opcode` parameter as you say.

https://github.com/llvm/llvm-project/pull/111479