[ic] Fix megamorphic stub cache probing on some platforms.

src/ic/s390/stub-cache-s390.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.
 
 #if V8_TARGET_ARCH_S390
 
 #include "src/ic/stub-cache.h"
 #include "src/codegen.h"
 #include "src/ic/ic.h"
 #include "src/interface-descriptors.h"
 
 namespace v8 {
 namespace internal {
 
 #define __ ACCESS_MASM(masm)
 
 static void ProbeTable(StubCache* stub_cache, MacroAssembler* masm,
                        Code::Flags flags, StubCache::Table table,
                        Register receiver, Register name,
-                       // Number of the cache entry, not scaled.
+                       // The offset is scaled by 4, based on
+                       // kCacheIndexShift, which is two bits
                        Register offset, Register scratch, Register scratch2,
                        Register offset_scratch) {
   ExternalReference key_offset(stub_cache->key_reference(table));
   ExternalReference value_offset(stub_cache->value_reference(table));
   ExternalReference map_offset(stub_cache->map_reference(table));
 
   uintptr_t key_off_addr = reinterpret_cast<uintptr_t>(key_offset.address());
   uintptr_t value_off_addr =
       reinterpret_cast<uintptr_t>(value_offset.address());
   uintptr_t map_off_addr = reinterpret_cast<uintptr_t>(map_offset.address());
@@ skipping 146 matching lines @@
   __ bind(&miss);
   __ IncrementCounter(counters->megamorphic_stub_cache_misses(), 1, extra2,
                       extra3);
 }
 
 #undef __
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_S390