[arm][arm64] Improve CountTrailingZero implementation.

src/compiler/wasm-compiler.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/wasm-compiler.h"
 
 #include "src/isolate-inl.h"
 
 #include "src/base/platform/platform.h"
 
@@ skipping 710 matching lines @@
     case wasm::kExprI32ReinterpretF32:
       op = m->BitcastFloat32ToInt32();
       break;
     case wasm::kExprI32Clz:
       op = m->Word32Clz();
       break;
     case wasm::kExprI32Ctz: {
       if (m->Word32Ctz().IsSupported()) {
         op = m->Word32Ctz().op();
         break;
+      } else if (m->Word32ReverseBits().IsSupported()) {
+        Node* reversed = graph()->NewNode(m->Word32ReverseBits().op(), input);
+        Node* result = graph()->NewNode(m->Word32Clz(), reversed);
+        return result;
       } else {
         return BuildI32Ctz(input);
       }
     }
     case wasm::kExprI32Popcnt: {
       if (m->Word32Popcnt().IsSupported()) {
         op = m->Word32Popcnt().op();
         break;
       } else {
         return BuildI32Popcnt(input);
@@ skipping 107 matching lines @@
     case wasm::kExprI64ReinterpretF64:
       op = m->BitcastFloat64ToInt64();
       break;
     case wasm::kExprI64Clz:
       op = m->Word64Clz();
       break;
     case wasm::kExprI64Ctz: {
       if (m->Word64Ctz().IsSupported()) {
         op = m->Word64Ctz().op();
         break;
+      } else if (m->Word64ReverseBits().IsSupported()) {
+        Node* reversed = graph()->NewNode(m->Word64ReverseBits().op(), input);
+        Node* result = graph()->NewNode(m->Word64Clz(), reversed);
+        return result;
       } else {
         return BuildI64Ctz(input);
       }
     }
     case wasm::kExprI64Popcnt: {
       if (m->Word64Popcnt().IsSupported()) {
         op = m->Word64Popcnt().op();
         break;
       } else {
         return BuildI64Popcnt(input);
@@ skipping 1281 matching lines @@
         module_env->module->GetName(function.name_offset));
   }
 
   return code;
 }
 
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8