ARM: More micro-optimization of megamorphic lookup.

src/arm/stub-cache-arm.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 187 matching lines @@
   __ JumpIfSmi(receiver, &miss);
 
   // Get the map of the receiver and compute the hash.
   __ ldr(scratch, FieldMemOperand(name, String::kHashFieldOffset));
   __ ldr(ip, FieldMemOperand(receiver, HeapObject::kMapOffset));
   __ add(scratch, scratch, Operand(ip));
   uint32_t mask = (kPrimaryTableSize - 1) << kHeapObjectTagSize;
   // Mask down the eor argument to the minimum to keep the immediate
   // ARM-encodable.
   __ eor(scratch, scratch, Operand(flags & mask));
-  // Prefer ubfx to and_ here because the mask is not ARM-encodable.
-  __ Ubfx(scratch, scratch, kHeapObjectTagSize, kPrimaryTableBits);
+  // Prefer and_ to ubfx here because ubfx takes 2 cycles.
+  __ and_(scratch, scratch, Operand(mask));
+  __ mov(scratch, Operand(scratch, LSR, 1));
 
   // Probe the primary table.
   ProbeTable(isolate,
              masm,
              flags,
              kPrimary,
              name,
              scratch,
-             kHeapObjectTagSize,
+             1,
              extra,
              extra2);
 
   // Primary miss: Compute hash for secondary probe.

[Michael Starzinger, 2012/02/02 15:36:08]

Can the following sequence be rewritten like follows? It is your call whether to
do that.

__ sub(scratch, scratch, Operand(name, LSR, 1));
__ add(scratch, scratch, Operand(flags >> 1));
__ and_(scratch,
        scratch,
        Operand((kSecondaryTableSize - 1) << kHeapObjectTagSize - 1));

-  __ rsb(scratch, name, Operand(scratch, LSL, kHeapObjectTagSize));
+  __ rsb(scratch, name, Operand(scratch, LSL, 1));
   __ add(scratch, scratch, Operand(flags));
-  __ Ubfx(scratch, scratch, kHeapObjectTagSize, kSecondaryTableBits);
+  __ and_(scratch,
+          scratch,
+          Operand((kSecondaryTableSize - 1) << kHeapObjectTagSize));
+  __ mov(scratch, Operand(scratch, LSR, 1));
 
   // Probe the secondary table.
   ProbeTable(isolate,
              masm,
              flags,
              kSecondary,
              name,
              scratch,
-             kHeapObjectTagSize,
+             1,
              extra,
              extra2);
 
   // Cache miss: Fall-through and let caller handle the miss by
   // entering the runtime system.
   __ bind(&miss);
 }
 
 
 void StubCompiler::GenerateLoadGlobalFunctionPrototype(MacroAssembler* masm,
@@ skipping 3999 matching lines @@
   Handle<Code> ic_miss = masm->isolate()->builtins()->KeyedStoreIC_Miss();
   __ Jump(ic_miss, RelocInfo::CODE_TARGET);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM