Improve ClampDoubleToUint8 on ia32/x64.

It's measured faster when:
a) clamp never happens;
b) clamp random happens ([-128,384], pseudo random).

Review URL: https://chromiumcodereview.appspot.com/11190049
Patch from Zheng Liu <zheng.z.liu@intel.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12777 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/ia32/lithium-ia32.cc

@@ -1779,7 +1779,7 @@ LInstruction* LChunkBuilder::DoClampToUint8(HClampToUint8* instr) {
   Representation input_rep = value->representation();
   if (input_rep.IsDouble()) {
     LOperand* reg = UseRegister(value);
-    return DefineAsRegister(new(zone()) LClampDToUint8(reg));
+    return DefineFixed(new(zone()) LClampDToUint8(reg), eax);
   } else if (input_rep.IsInteger32()) {
     LOperand* reg = UseFixed(value, eax);
     return DefineFixed(new(zone()) LClampIToUint8(reg), eax);

src/ia32/macro-assembler-ia32.cc

@@ -129,14 +129,22 @@ void MacroAssembler::ClampDoubleToUint8(XMMRegister input_reg,
                                         XMMRegister scratch_reg,
                                         Register result_reg) {
   Label done;
-  ExternalReference zero_ref = ExternalReference::address_of_zero();
-  movdbl(scratch_reg, Operand::StaticVariable(zero_ref));
-  Set(result_reg, Immediate(0));
-  ucomisd(input_reg, scratch_reg);
-  j(below, &done, Label::kNear);
+  Label conv_failure;
+  pxor(scratch_reg, scratch_reg);
   cvtsd2si(result_reg, input_reg);
   test(result_reg, Immediate(0xFFFFFF00));
   j(zero, &done, Label::kNear);
+  cmp(result_reg, Immediate(0x80000000));
+  j(equal, &conv_failure, Label::kNear);
+  mov(result_reg, Immediate(0));
+  setcc(above, result_reg);
+  sub(result_reg, Immediate(1));
+  and_(result_reg, Immediate(255));
+  jmp(&done, Label::kNear);
+  bind(&conv_failure);
+  Set(result_reg, Immediate(0));
+  ucomisd(input_reg, scratch_reg);
+  j(below, &done, Label::kNear);
   Set(result_reg, Immediate(255));
   bind(&done);
 }

src/x64/lithium-codegen-x64.cc

@@ -4490,8 +4490,7 @@ void LCodeGen::DoCheckMaps(LCheckMaps* instr) {
 void LCodeGen::DoClampDToUint8(LClampDToUint8* instr) {
   XMMRegister value_reg = ToDoubleRegister(instr->unclamped());
   Register result_reg = ToRegister(instr->result());
-  Register temp_reg = ToRegister(instr->temp());
-  __ ClampDoubleToUint8(value_reg, xmm0, result_reg, temp_reg);
+  __ ClampDoubleToUint8(value_reg, xmm0, result_reg);
 }
 
 
@@ -4505,8 +4504,7 @@ void LCodeGen::DoClampIToUint8(LClampIToUint8* instr) {
 void LCodeGen::DoClampTToUint8(LClampTToUint8* instr) {
   ASSERT(instr->unclamped()->Equals(instr->result()));
   Register input_reg = ToRegister(instr->unclamped());
-  Register temp_reg = ToRegister(instr->temp());
-  XMMRegister temp_xmm_reg = ToDoubleRegister(instr->temp2());
+  XMMRegister temp_xmm_reg = ToDoubleRegister(instr->temp_xmm());
   Label is_smi, done, heap_number;
 
   __ JumpIfSmi(input_reg, &is_smi);
@@ -4526,7 +4524,7 @@ void LCodeGen::DoClampTToUint8(LClampTToUint8* instr) {
   // Heap number
   __ bind(&heap_number);
   __ movsd(xmm0, FieldOperand(input_reg, HeapNumber::kValueOffset));
-  __ ClampDoubleToUint8(xmm0, temp_xmm_reg, input_reg, temp_reg);
+  __ ClampDoubleToUint8(xmm0, temp_xmm_reg, input_reg);
   __ jmp(&done, Label::kNear);
 
   // smi

src/x64/lithium-x64.cc

@@ -1697,8 +1697,7 @@ LInstruction* LChunkBuilder::DoClampToUint8(HClampToUint8* instr) {
   Representation input_rep = value->representation();
   LOperand* reg = UseRegister(value);
   if (input_rep.IsDouble()) {
-    return DefineAsRegister(new(zone()) LClampDToUint8(reg,
-                                               TempRegister()));
+    return DefineAsRegister(new(zone()) LClampDToUint8(reg));
   } else if (input_rep.IsInteger32()) {
     return DefineSameAsFirst(new(zone()) LClampIToUint8(reg));
   } else {
@@ -1706,7 +1705,6 @@ LInstruction* LChunkBuilder::DoClampToUint8(HClampToUint8* instr) {
     // Register allocator doesn't (yet) support allocation of double
     // temps. Reserve xmm1 explicitly.
     LClampTToUint8* result = new(zone()) LClampTToUint8(reg,
-                                                        TempRegister(),
                                                         FixedTemp(xmm1));
     return AssignEnvironment(DefineSameAsFirst(result));
   }

src/x64/lithium-x64.h

@@ -2138,15 +2138,13 @@ class LCheckSmi: public LTemplateInstruction<0, 1, 0> {
 };
 
 
-class LClampDToUint8: public LTemplateInstruction<1, 1, 1> {
+class LClampDToUint8: public LTemplateInstruction<1, 1, 0> {
  public:
-  LClampDToUint8(LOperand* unclamped, LOperand* temp) {
+  explicit LClampDToUint8(LOperand* unclamped) {
     inputs_[0] = unclamped;
-    temps_[0] = temp;
   }
 
   LOperand* unclamped() { return inputs_[0]; }
-  LOperand* temp() { return temps_[0]; }
 
   DECLARE_CONCRETE_INSTRUCTION(ClampDToUint8, "clamp-d-to-uint8")
 };
@@ -2164,19 +2162,16 @@ class LClampIToUint8: public LTemplateInstruction<1, 1, 0> {
 };
 
 
-class LClampTToUint8: public LTemplateInstruction<1, 1, 2> {
+class LClampTToUint8: public LTemplateInstruction<1, 1, 1> {
  public:
   LClampTToUint8(LOperand* unclamped,
-                 LOperand* temp,
-                 LOperand* temp2) {
+                 LOperand* temp_xmm) {
     inputs_[0] = unclamped;
-    temps_[0] = temp;
-    temps_[1] = temp2;
+    temps_[0] = temp_xmm;
   }
 
   LOperand* unclamped() { return inputs_[0]; }
-  LOperand* temp() { return temps_[0]; }
-  LOperand* temp2() { return temps_[1]; }
+  LOperand* temp_xmm() { return temps_[0]; }
 
   DECLARE_CONCRETE_INSTRUCTION(ClampTToUint8, "clamp-t-to-uint8")
 };

src/x64/macro-assembler-x64.cc

@@ -2868,16 +2868,24 @@ void MacroAssembler::ClampUint8(Register reg) {
 
 void MacroAssembler::ClampDoubleToUint8(XMMRegister input_reg,
                                         XMMRegister temp_xmm_reg,
-                                        Register result_reg,
-                                        Register temp_reg) {
+                                        Register result_reg) {
   Label done;
-  Set(result_reg, 0);
+  Label conv_failure;
   xorps(temp_xmm_reg, temp_xmm_reg);
-  ucomisd(input_reg, temp_xmm_reg);
-  j(below, &done, Label::kNear);
   cvtsd2si(result_reg, input_reg);
   testl(result_reg, Immediate(0xFFFFFF00));
   j(zero, &done, Label::kNear);
+  cmpl(result_reg, Immediate(0x80000000));
+  j(equal, &conv_failure, Label::kNear);
+  movl(result_reg, Immediate(0));
+  setcc(above, result_reg);
+  subl(result_reg, Immediate(1));
+  andl(result_reg, Immediate(255));
+  jmp(&done, Label::kNear);
+  bind(&conv_failure);
+  Set(result_reg, 0);
+  ucomisd(input_reg, temp_xmm_reg);
+  j(below, &done, Label::kNear);
   Set(result_reg, 255);
   bind(&done);
 }

src/x64/macro-assembler-x64.h

@@ -942,8 +942,7 @@ class MacroAssembler: public Assembler {
 
   void ClampDoubleToUint8(XMMRegister input_reg,
                           XMMRegister temp_xmm_reg,
-                          Register result_reg,
-                          Register temp_reg);
+                          Register result_reg);
 
   void LoadUint32(XMMRegister dst, Register src, XMMRegister scratch);