[llvm] [LLVM][CostModel][AArch64] Remove magic numbers from f16 vector compares. (PR #135795)

[David Green via llvm-commits]

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@@ -4236,10 +4236,34 @@ InstructionCost AArch64TTIImpl::getCmpSelInstrCost(
   }
 
   if (isa<FixedVectorType>(ValTy) && ISD == ISD::SETCC) {
-    auto LT = getTypeLegalizationCost(ValTy);
-    // Cost v4f16 FCmp without FP16 support via converting to v4f32 and back.
-    if (LT.second == MVT::v4f16 && !ST->hasFullFP16())
-      return LT.first * 4; // fcvtl + fcvtl + fcmp + xtn
+    Type *ValScalarTy = ValTy->getScalarType();
+    if ((ValScalarTy->isHalfTy() && !ST->hasFullFP16()) ||
+        ValScalarTy->isBFloatTy()) {
+      auto *ValVTy = cast<FixedVectorType>(ValTy);
+
+      // FIXME: We currently scalarise these.
+      if (ValVTy->getNumElements() > 4)
+        return BaseT::getCmpSelInstrCost(Opcode, ValTy, CondTy, VecPred,
+                                         CostKind, Op1Info, Op2Info, I);
+
+      // Without dedicated instructions we promote [b]f16 compares to f32.
+      auto *PromotedTy =
+          VectorType::get(Type::getFloatTy(ValTy->getContext()), ValVTy);
+
+      InstructionCost Cost = 0;
+      // Promte operands to float vectors.
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davemgreen wrote:

Promte->Promote

https://github.com/llvm/llvm-project/pull/135795