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

[Derek Schuff 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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dschuff wrote:

How do we model the different shuffles? It makes sense that different shuffles would have different costs because of different native lowerings, but are those more explicitly encoded anywhere in LLVM?

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