[llvm] [WebAssembly] Implement more of getCastInstrCost (PR #164612)

[Sam Parker via llvm-commits]

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@@ -119,18 +119,82 @@ InstructionCost WebAssemblyTTIImpl::getCastInstrCost(
     }
   }
 
-  // extend_low
   static constexpr TypeConversionCostTblEntry ConversionTbl[] = {
+      // extend_low
       {ISD::SIGN_EXTEND, MVT::v2i64, MVT::v2i32, 1},
       {ISD::ZERO_EXTEND, MVT::v2i64, MVT::v2i32, 1},
       {ISD::SIGN_EXTEND, MVT::v4i32, MVT::v4i16, 1},
       {ISD::ZERO_EXTEND, MVT::v4i32, MVT::v4i16, 1},
       {ISD::SIGN_EXTEND, MVT::v8i16, MVT::v8i8, 1},
       {ISD::ZERO_EXTEND, MVT::v8i16, MVT::v8i8, 1},
+      // 2 x extend_low
       {ISD::SIGN_EXTEND, MVT::v2i64, MVT::v2i16, 2},
       {ISD::ZERO_EXTEND, MVT::v2i64, MVT::v2i16, 2},
       {ISD::SIGN_EXTEND, MVT::v4i32, MVT::v4i8, 2},
       {ISD::ZERO_EXTEND, MVT::v4i32, MVT::v4i8, 2},
+      // extend_low, extend_high
+      {ISD::SIGN_EXTEND, MVT::v4i64, MVT::v4i32, 2},
+      {ISD::ZERO_EXTEND, MVT::v4i64, MVT::v4i32, 2},
+      {ISD::SIGN_EXTEND, MVT::v8i32, MVT::v8i16, 2},
+      {ISD::ZERO_EXTEND, MVT::v8i32, MVT::v8i16, 2},
+      {ISD::SIGN_EXTEND, MVT::v16i16, MVT::v16i8, 2},
+      {ISD::ZERO_EXTEND, MVT::v16i16, MVT::v16i8, 2},
+      // 2x extend_low, extend_high
+      {ISD::SIGN_EXTEND, MVT::v8i64, MVT::v8i32, 4},
+      {ISD::ZERO_EXTEND, MVT::v8i64, MVT::v8i32, 4},
+      {ISD::SIGN_EXTEND, MVT::v16i32, MVT::v16i16, 4},
+      {ISD::ZERO_EXTEND, MVT::v16i32, MVT::v16i16, 4},
+      // shuffle
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sparker-arm wrote:

We don't do any explicit modelling yet, so we need to implement `getShuffleCost`. Hopefully `getInterleavedMemoryOpCost` can then use that too, as well as here. In V8, I've added `CanonicalShuffles` which recognise predefined shuffle patterns so I could use that as a base to understand which shuffles are easier than others.

https://github.com/llvm/llvm-project/pull/164612