[llvm] [AArch64] Add costs for ROTR and ROTL. (PR #169335)

[Matthew Devereau via llvm-commits]

================
@@ -921,8 +921,19 @@ AArch64TTIImpl::getIntrinsicInstrCost(const IntrinsicCostAttributes &ICA,
     if (ICA.getArgs().empty())
       break;
 
-    // TODO: Add handling for fshl where third argument is not a constant.
     const TTI::OperandValueInfo OpInfoZ = TTI::getOperandInfo(ICA.getArgs()[2]);
+
+    // ROTR / ROTL on integer registers can be done in a single instruction. A
+    // fshl with a non-constant shift uses a neg + ror.
+    if (RetTy->isIntegerTy() && ICA.getArgs()[0] == ICA.getArgs()[1] &&
+        (RetTy->getPrimitiveSizeInBits() == 32 ||
+         RetTy->getPrimitiveSizeInBits() == 64)) {
+      InstructionCost NegCost =
+          (ICA.getID() == Intrinsic::fshl && !OpInfoZ.isConstant()) ? 1 : 0;
+      return 1 + NegCost;
----------------
MDevereau wrote:

Can you just do
```suggestion
      return 1 + (ICA.getID() == Intrinsic::fshl && !OpInfoZ.isConstant());
```
?

https://github.com/llvm/llvm-project/pull/169335