[wasm] Handle simple opcodes specially

Avoid the indirection via the signature, instead specialize per
signature. On a microbenchmark run locally, this speeds up Liftoff by
~5% and validation by ~15%.

R=titzer@chromium.org

Bug: v8:8423
Change-Id: Ia0e9ab0dcaa759e4ed4dcd46d2e6f16e65790915
Reviewed-on: https://chromium-review.googlesource.com/c/1373778Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58241}

src/wasm/wasm-opcodes.cc

@@ -475,20 +475,8 @@ constexpr std::array<WasmOpcodeSig, 256> kAtomicExprSigTable =
 constexpr std::array<WasmOpcodeSig, 256> kNumericExprSigTable =
     base::make_array<256>(GetNumericOpcodeSigIndex{});
 
-// Computes a direct pointer to a cached signature for a simple opcode.
-struct GetSimpleOpcodeSig {
-  constexpr const FunctionSig* operator()(byte opcode) const {
-#define CASE(name, opc, sig) opcode == opc ? &kSig_##sig:
-    return FOREACH_SIMPLE_OPCODE(CASE) nullptr;
-#undef CASE
-  }
-};
-
 }  // namespace
 
-const std::array<const FunctionSig*, 256> kSimpleOpcodeSigs =
-    base::make_array<256>(GetSimpleOpcodeSig{});
-
 FunctionSig* WasmOpcodes::Signature(WasmOpcode opcode) {
   switch (opcode >> 8) {
     case 0:

src/wasm/wasm-opcodes.h

@@ -576,8 +576,6 @@ enum TrapReason {
 #undef DECLARE_ENUM
 };
 
-extern const std::array<const FunctionSig*, 256> kSimpleOpcodeSigs;
-
 // A collection of opcode-related static methods.
 class V8_EXPORT_PRIVATE WasmOpcodes {
  public: