[asm.js] Cleanup function import signature caching.

This simplifies the double-indirection used for the signature cache in
function imports and also reduces the memory its memory footprint. Also
switch to use the local zone as an underlying storage.

R=rossberg@chromium.org
BUG=v8:6127

Change-Id: I8bc6cf13f2ce9ffa02485e76b7e36f389c9e02e5
Reviewed-on: https://chromium-review.googlesource.com/483443Reviewed-by: Andreas Rossberg <rossberg@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44768}

src/asmjs/asm-parser.cc

@@ -550,8 +550,9 @@ bool AsmJsParser::ValidateModuleVarImport(VarInfo* info,
       return true;
     }
     info->kind = VarKind::kImportedFunction;
-    function_import_info_.resize(function_import_info_.size() + 1);
-    info->import = &function_import_info_.back();
+    info->import =
+        new (zone()->New(sizeof(FunctionImportInfo))) FunctionImportInfo(
+            {nullptr, 0, WasmModuleBuilder::SignatureMap(zone())});
     // TODO(bradnelson): Refactor memory management here.
     // AsmModuleBuilder should really own import names.
     info->import->function_name = zone()->NewArray<char>(import_name.size());
@@ -2162,16 +2163,16 @@ AsmType* AsmJsParser::ValidateCall() {
     }
     DCHECK(function_info->import != nullptr);
     // TODO(bradnelson): Factor out.
-    uint32_t cache_index = function_info->import->cache.FindOrInsert(sig);
     uint32_t index;
-    if (cache_index >= function_info->import->cache_index.size()) {
+    auto it = function_info->import->cache.find(sig);
+    if (it != function_info->import->cache.end()) {
+      index = it->second;
+    } else {
       index = module_builder_->AddImport(
           function_info->import->function_name,
           static_cast<uint32_t>(function_info->import->function_name_size),
           sig);
-      function_info->import->cache_index.push_back(index);
-    } else {
-      index = function_info->import->cache_index[cache_index];
+      function_info->import->cache[sig] = index;
     }
     current_function_builder_->AddAsmWasmOffset(call_pos, to_number_pos);
     current_function_builder_->Emit(kExprCallFunction);

src/asmjs/asm-parser.h

@@ -5,14 +5,12 @@
 #ifndef V8_ASMJS_ASM_PARSER_H_
 #define V8_ASMJS_ASM_PARSER_H_
 
-#include <list>
 #include <string>
 #include <vector>
 
 #include "src/asmjs/asm-scanner.h"
 #include "src/asmjs/asm-typer.h"
 #include "src/asmjs/asm-types.h"
-#include "src/wasm/signature-map.h"
 #include "src/wasm/wasm-module-builder.h"
 #include "src/zone/zone-containers.h"
 
@@ -61,8 +59,7 @@ class AsmJsParser {
   struct FunctionImportInfo {
     char* function_name;
     size_t function_name_size;
-    SignatureMap cache;
-    std::vector<uint32_t> cache_index;
+    WasmModuleBuilder::SignatureMap cache;
   };
 
   struct VarInfo {
@@ -100,9 +97,8 @@ class AsmJsParser {
   WasmModuleBuilder* module_builder_;
   WasmFunctionBuilder* current_function_builder_;
   AsmType* return_type_;
-  std::uintptr_t stack_limit_;
+  uintptr_t stack_limit_;
   AsmTyper::StdlibSet stdlib_uses_;
-  std::list<FunctionImportInfo> function_import_info_;
   ZoneVector<VarInfo> global_var_info_;
   ZoneVector<VarInfo> local_var_info_;