[llvm] [AArch64] Add sve bf16 fpext and fpround costs. (PR #150485)

[Paul Walker via llvm-commits]

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@@ -3093,6 +3093,12 @@ InstructionCost AArch64TTIImpl::getCastInstrCost(unsigned Opcode, Type *Dst,
       {ISD::FP_ROUND, MVT::v2bf16, MVT::v2f64, 2}, // bfcvtn+fcvtn
       {ISD::FP_ROUND, MVT::v4bf16, MVT::v4f64, 3}, // fcvtn+fcvtl2+bfcvtn
       {ISD::FP_ROUND, MVT::v8bf16, MVT::v8f64, 6}, // 2 * fcvtn+fcvtn2+bfcvtn
+      {ISD::FP_ROUND, MVT::nxv2bf16, MVT::nxv2f32, 1}, // bfcvt
+      {ISD::FP_ROUND, MVT::nxv4bf16, MVT::nxv4f32, 1}, // bfcvt
+      {ISD::FP_ROUND, MVT::nxv8bf16, MVT::nxv8f32, 3}, // bfcvt+bfcvt+uzp1
+      {ISD::FP_ROUND, MVT::nxv2bf16, MVT::nxv2f64, 2}, // fcvtx+bfcvt
+      {ISD::FP_ROUND, MVT::nxv4bf16, MVT::nxv4f64, 5}, // fcvtx+bfcvt+bfcvt+uzp1
+      {ISD::FP_ROUND, MVT::nxv8bf16, MVT::nxv8f64, 11}, // 4*fcvt+4*bfcvt+3*uzp
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paulwalker-arm wrote:

`fcvtx` requires SVE2 and there's no support for scalable vector double -> bfloat conversions without it.

https://github.com/llvm/llvm-project/pull/150485