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

src/ic/arm/stub-cache-arm.cc

 // Copyright 2012 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_ARM
 
 #include "src/codegen.h"
 #include "src/ic/ic.h"
 #include "src/ic/stub-cache.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));
 
   uint32_t key_off_addr = reinterpret_cast<uint32_t>(key_offset.address());
   uint32_t value_off_addr = reinterpret_cast<uint32_t>(value_offset.address());
   uint32_t map_off_addr = reinterpret_cast<uint32_t>(map_offset.address());
 
   // Check the relative positions of the address fields.
   DCHECK(value_off_addr > key_off_addr);
   DCHECK((value_off_addr - key_off_addr) % 4 == 0);
   DCHECK((value_off_addr - key_off_addr) < (256 * 4));
   DCHECK(map_off_addr > key_off_addr);
   DCHECK((map_off_addr - key_off_addr) % 4 == 0);
   DCHECK((map_off_addr - key_off_addr) < (256 * 4));
 
   Label miss;
   Register base_addr = scratch;
   scratch = no_reg;
 
   // Multiply by 3 because there are 3 fields per entry (name, code, map).
   __ add(offset_scratch, offset, Operand(offset, LSL, 1));
 
   // Calculate the base address of the entry.
-  __ mov(base_addr, Operand(key_offset));
-  __ add(base_addr, base_addr, Operand(offset_scratch, LSL, kPointerSizeLog2));
+  __ add(base_addr, offset_scratch, Operand(key_offset));
 
   // Check that the key in the entry matches the name.
   __ ldr(ip, MemOperand(base_addr, 0));
   __ cmp(name, ip);
   __ b(ne, &miss);
 
   // Check the map matches.
   __ ldr(ip, MemOperand(base_addr, map_off_addr - key_off_addr));
   __ ldr(scratch2, FieldMemOperand(receiver, HeapObject::kMapOffset));
   __ cmp(ip, scratch2);
@@ skipping 74 matching lines @@
   __ IncrementCounter(counters->megamorphic_stub_cache_probes(), 1, extra2,
                       extra3);
 
   // Check that the receiver isn't a smi.
   __ JumpIfSmi(receiver, &miss);
 
   // Get the map of the receiver and compute the hash.
   __ ldr(scratch, FieldMemOperand(name, Name::kHashFieldOffset));
   __ ldr(ip, FieldMemOperand(receiver, HeapObject::kMapOffset));
   __ add(scratch, scratch, Operand(ip));
-  uint32_t mask = kPrimaryTableSize - 1;
-  // We shift out the last two bits because they are not part of the hash and
-  // they are always 01 for maps.
-  __ mov(scratch, Operand(scratch, LSR, kCacheIndexShift));
-  // Mask down the eor argument to the minimum to keep the immediate
-  // ARM-encodable.
-  __ eor(scratch, scratch, Operand((flags >> kCacheIndexShift) & mask));
-  // Prefer and_ to ubfx here because ubfx takes 2 cycles.
-  __ and_(scratch, scratch, Operand(mask));
+  __ eor(scratch, scratch, Operand(flags));
+  __ mov(ip, Operand(kPrimaryTableSize - 1));
+  __ and_(scratch, scratch, Operand(ip, LSL, kCacheIndexShift));
 
   // Probe the primary table.
   ProbeTable(this, masm, flags, kPrimary, receiver, name, scratch, extra,
              extra2, extra3);
 
   // Primary miss: Compute hash for secondary probe.
-  __ sub(scratch, scratch, Operand(name, LSR, kCacheIndexShift));
-  uint32_t mask2 = kSecondaryTableSize - 1;
-  __ add(scratch, scratch, Operand((flags >> kCacheIndexShift) & mask2));
-  __ and_(scratch, scratch, Operand(mask2));
+  __ sub(scratch, scratch, Operand(name));
+  __ add(scratch, scratch, Operand(flags));
+  __ mov(ip, Operand(kSecondaryTableSize - 1));
+  __ and_(scratch, scratch, Operand(ip, LSL, kCacheIndexShift));
 
   // Probe the secondary table.
   ProbeTable(this, masm, flags, kSecondary, receiver, name, scratch, extra,
              extra2, extra3);
 
   // Cache miss: Fall-through and let caller handle the miss by
   // entering the runtime system.
   __ bind(&miss);
   __ IncrementCounter(counters->megamorphic_stub_cache_misses(), 1, extra2,
                       extra3);
 }
 
 
 #undef __
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_ARM