Some assembler-level optimizations on ARM.

src/arm/lithium-codegen-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 3910 matching lines @@
                                 bool deoptimize_on_undefined,
                                 bool deoptimize_on_minus_zero,
                                 LEnvironment* env) {
   Register scratch = scratch0();
   SwVfpRegister flt_scratch = double_scratch0().low();
   ASSERT(!result_reg.is(double_scratch0()));
 
   Label load_smi, heap_number, done;
 
   // Smi check.
-  __ JumpIfSmi(input_reg, &load_smi);
+  STATIC_CHECK(kSmiTagSize == 1 && kSmiTag == 0);

[ulan, 2012/01/27 13:19:11]

UntagAndJumpIfSmi

+  __ mov(scratch, Operand(input_reg, ASR, kSmiTagSize), SetCC);
+  __ b(cc, &load_smi);  // Shifter carry is not set for a smi.
 
   // Heap number map check.
   __ ldr(scratch, FieldMemOperand(input_reg, HeapObject::kMapOffset));
   __ LoadRoot(ip, Heap::kHeapNumberMapRootIndex);
   __ cmp(scratch, Operand(ip));
   if (deoptimize_on_undefined) {
     DeoptimizeIf(ne, env);
   } else {
     Label heap_number;
     __ b(eq, &heap_number);
@@ skipping 18 matching lines @@
     __ cmp(ip, Operand(0));
     __ b(ne, &done);
     __ vmov(ip, result_reg.high());
     __ cmp(ip, Operand(HeapNumber::kSignMask));
     DeoptimizeIf(eq, env);
   }
   __ jmp(&done);
 
   // Smi to double register conversion
   __ bind(&load_smi);
-  __ SmiUntag(input_reg);  // Untag smi before converting to float.
-  __ vmov(flt_scratch, input_reg);
+  // scratch: untagged value of input_reg
+  __ vmov(flt_scratch, scratch);
   __ vcvt_f64_s32(result_reg, flt_scratch);
-  __ SmiTag(input_reg);  // Retag smi.
   __ bind(&done);
 }
 
 
 void LCodeGen::DoDeferredTaggedToI(LTaggedToI* instr) {
   Register input_reg = ToRegister(instr->InputAt(0));
   Register scratch1 = scratch0();
   Register scratch2 = ToRegister(instr->TempAt(0));
   DwVfpRegister double_scratch = double_scratch0();
   SwVfpRegister single_scratch = double_scratch.low();
@@ skipping 265 matching lines @@
 
 
 void LCodeGen::DoClampTToUint8(LClampTToUint8* instr) {
   Register scratch = scratch0();
   Register input_reg = ToRegister(instr->unclamped());
   Register result_reg = ToRegister(instr->result());
   DoubleRegister temp_reg = ToDoubleRegister(instr->TempAt(0));
   Label is_smi, done, heap_number;
 
   // Both smi and heap number cases are handled.
-  __ JumpIfSmi(input_reg, &is_smi);
+  STATIC_ASSERT(kSmiTagSize == 1 && kSmiTag == 0);
+  __ mov(result_reg, Operand(input_reg, ASR, kSmiTagSize), SetCC);
+  __ b(cc, &is_smi);  // Shifter carry is not set for a smi.
 
   // Check for heap number
   __ ldr(scratch, FieldMemOperand(input_reg, HeapObject::kMapOffset));
   __ cmp(scratch, Operand(factory()->heap_number_map()));
   __ b(eq, &heap_number);
 
   // Check for undefined. Undefined is converted to zero for clamping
   // conversions.
   __ cmp(input_reg, Operand(factory()->undefined_value()));
   DeoptimizeIf(ne, instr->environment());
   __ mov(result_reg, Operand(0));
   __ jmp(&done);
 
   // Heap number
   __ bind(&heap_number);
   __ vldr(double_scratch0(), FieldMemOperand(input_reg,
                                              HeapNumber::kValueOffset));
   __ ClampDoubleToUint8(result_reg, double_scratch0(), temp_reg);
   __ jmp(&done);
 
   // smi
   __ bind(&is_smi);
-  __ SmiUntag(result_reg, input_reg);
   __ ClampUint8(result_reg, result_reg);
 
   __ bind(&done);
 }
 
 
 void LCodeGen::DoCheckPrototypeMaps(LCheckPrototypeMaps* instr) {
   Register temp1 = ToRegister(instr->TempAt(0));
   Register temp2 = ToRegister(instr->TempAt(1));
 
@@ skipping 507 matching lines @@
   ASSERT(osr_pc_offset_ == -1);
   osr_pc_offset_ = masm()->pc_offset();
 }
 
 
 
 
 #undef __
 
 } }  // namespace v8::internal