Bug 910796 - SpiderMonkey: Micro-optimize clampIntToUint8. r=mjrosenb

js/src/jit/BaselineIC.cpp

@@ -5183,7 +5183,7 @@ ICSetElem_TypedArray::Compiler::generateStubCode(MacroAssembler &masm)
         Label notInt32;
         masm.branchTestInt32(Assembler::NotEqual, value, &notInt32);
         masm.unboxInt32(value, secondScratch);
-        masm.clampIntToUint8(secondScratch, secondScratch);
+        masm.clampIntToUint8(secondScratch);
 
         Label clamped;
         masm.bind(&clamped);

js/src/jit/CodeGenerator.cpp

@@ -6756,9 +6756,9 @@ CodeGenerator::visitStoreTypedArrayElementHole(LStoreTypedArrayElementHole *lir)
 bool
 CodeGenerator::visitClampIToUint8(LClampIToUint8 *lir)
 {
-    Register input = ToRegister(lir->input());
     Register output = ToRegister(lir->output());
-    masm.clampIntToUint8(input, output);
+    JS_ASSERT(output == ToRegister(lir->input()));
+    masm.clampIntToUint8(output);
     return true;
 }
 

js/src/jit/IonMacroAssembler.cpp

@@ -1629,7 +1629,7 @@ MacroAssembler::convertValueToInt(ValueOperand value, MDefinition *maybeInput,
         bind(&isInt32);
         unboxInt32(value, output);
         if (behavior == IntConversion_ClampToUint8)
-            clampIntToUint8(output, output);
+            clampIntToUint8(output);
     }
 
     bind(&done);

js/src/jit/Lowering.cpp

@@ -2386,7 +2386,7 @@ LIRGenerator::visitClampToUint8(MClampToUint8 *ins)
         return redefine(ins, in);
 
       case MIRType_Int32:
-        return define(new LClampIToUint8(useRegisterAtStart(in)), ins);
+        return defineReuseInput(new LClampIToUint8(useRegisterAtStart(in)), ins, 0);
 
       case MIRType_Double:
         return define(new LClampDToUint8(useRegisterAtStart(in), tempCopy(in, 0)), ins);

js/src/jit/arm/MacroAssembler-arm.h

@@ -1264,13 +1264,12 @@ class MacroAssemblerARMCompat : public MacroAssemblerARM
         ma_vstr(VFPRegister(src).singleOverlay(), addr.base, addr.index, scale);
     }
 
-    void clampIntToUint8(Register src, Register dest) {
-        // look at (src >> 8) if it is 0, then src shouldn't be clamped
+    void clampIntToUint8(Register reg) {
+        // look at (reg >> 8) if it is 0, then reg shouldn't be clamped
         // if it is <0, then we want to clamp to 0, otherwise, we wish to clamp to 255
-        as_mov(ScratchRegister, asr(src, 8), SetCond);
-        ma_mov(src, dest);
-        ma_mov(Imm32(0xff), dest, NoSetCond, NotEqual);
-        ma_mov(Imm32(0), dest, NoSetCond, Signed);
+        as_mov(ScratchRegister, asr(reg, 8), SetCond);
+        ma_mov(Imm32(0xff), reg, NoSetCond, NotEqual);
+        ma_mov(Imm32(0), reg, NoSetCond, Signed);
     }
 
     void cmp32(const Register &lhs, const Imm32 &rhs);

js/src/jit/shared/MacroAssembler-x86-shared.h

@@ -423,26 +423,15 @@ class MacroAssemblerX86Shared : public Assembler
         }
     }
 
-    void clampIntToUint8(Register src, Register dest) {
-        Label inRange, done;
-        branchTest32(Assembler::Zero, src, Imm32(0xffffff00), &inRange);
+    void clampIntToUint8(Register reg) {
+        Label inRange;
+        branchTest32(Assembler::Zero, reg, Imm32(0xffffff00), &inRange);
         {
-            Label negative;
-            branchTest32(Assembler::Signed, src, src, &negative);
-            {
-                movl(Imm32(255), dest);
-                jump(&done);
-            }
-            bind(&negative);
-            {
-                xorl(dest, dest);
-                jump(&done);
-            }
+            sarl(Imm32(31), reg);
+            notl(reg);
+            andl(Imm32(255), reg);
         }
         bind(&inRange);
-        if (src != dest)
-            movl(src, dest);
-        bind(&done);
     }
 
     bool maybeInlineDouble(double d, const FloatRegister &dest) {