[llvm] [LV] Add on extra cost for scalarising math calls in vector loops (PR #158611)

[David Sherwood via llvm-commits]

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@@ -1004,10 +1016,44 @@ AArch64TTIImpl::getIntrinsicInstrCost(const IntrinsicCostAttributes &ICA,
     }
     break;
   }
+  case Intrinsic::asin:
+  case Intrinsic::acos:
+  case Intrinsic::atan:
+  case Intrinsic::atan2:
+  case Intrinsic::sin:
+  case Intrinsic::cos:
+  case Intrinsic::tan:
+  case Intrinsic::sinh:
+  case Intrinsic::cosh:
+  case Intrinsic::tanh:
+  case Intrinsic::pow:
+  case Intrinsic::exp:
+  case Intrinsic::exp10:
+  case Intrinsic::exp2:
+  case Intrinsic::log:
+  case Intrinsic::log10:
+  case Intrinsic::log2: {
+    if (auto *FixedVTy = dyn_cast<FixedVectorType>(RetTy))
+      BaseCost = getCallScalarizationCost(FixedVTy->getElementCount());
+    break;
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david-arm wrote:

We could add it to the cost of scalarisation of the return type, but I didn't do this for two reasons:

1. Does the return type guarantee to represent the VF of the loop in all cases? Probably for math calls this is true as we'll always return a value.
2. We'd also have to pass in an extra Instruction pointer to provide context so that we only increase the cost for calls. It felt a bit awkward expanding the interface for this one case.

https://github.com/llvm/llvm-project/pull/158611