Reviewers: Lasse Reichstein,
Message:
I will test the performance impact of using the sign flag test instead of
the
-0.5 test in the ignore_negative_zero case.
Description:
Fix optimized code for Math.round on ia32 platform.
Please review this at http://codereview.chromium.org/6838012/
SVN Base: http://v8.googlecode.com/svn/branches/bleeding_edge/
Affected files:
M src/ia32/lithium-codegen-ia32.cc
Index: src/ia32/lithium-codegen-ia32.cc
===================================================================
--- src/ia32/lithium-codegen-ia32.cc (revision 7599)
+++ src/ia32/lithium-codegen-ia32.cc (working copy)
@@ -2707,25 +2707,16 @@
Register output_reg = ToRegister(instr->result());
XMMRegister input_reg = ToDoubleRegister(instr->InputAt(0));
+ Label below_half, done;
// xmm_scratch = 0.5
ExternalReference one_half = ExternalReference::address_of_one_half();
__ movdbl(xmm_scratch, Operand::StaticVariable(one_half));
+ __ ucomisd(xmm_scratch, input_reg);
+ __ j(above, &below_half);
// input = input + 0.5
__ addsd(input_reg, xmm_scratch);
- // We need to return -0 for the input range [-0.5, 0[, otherwise
- // compute Math.floor(value + 0.5).
- if (instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero)) {
- __ ucomisd(input_reg, xmm_scratch);
- DeoptimizeIf(below_equal, instr->environment());
- } else {
- // If we don't need to bailout on -0, we check only bailout
- // on negative inputs.
- __ xorpd(xmm_scratch, xmm_scratch); // Zero the register.
- __ ucomisd(input_reg, xmm_scratch);
- DeoptimizeIf(below, instr->environment());
- }
// Compute Math.floor(value + 0.5).
// Use truncating instruction (OK because input is positive).
@@ -2734,6 +2725,27 @@
// Overflow is signalled with minint.
__ cmp(output_reg, 0x80000000u);
DeoptimizeIf(equal, instr->environment());
+ __ jmp(&done);
+
+ __ bind(&below_half);
+
+ // We return 0 for the input range [+0, 0.5[, or [-0.5, 0.5[ if
+ // we can ignore the difference between a result of -0 and +0.
+ if (instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero)) {
+ // If the sign is positive, we return +0.
+ __ movmskpd(output_reg, input_reg);
+ __ test(output_reg, Immediate(1));
+ DeoptimizeIf(not_zero, instr->environment());
+ } else {
+ // If the input is >= -0.5, we return +0.
+ __ mov(output_reg, Immediate(0xBF000000));
+ __ movd(xmm_scratch, Operand(output_reg));
+ __ cvtss2sd(xmm_scratch, xmm_scratch);
+ __ ucomisd(input_reg, xmm_scratch);
+ DeoptimizeIf(below, instr->environment());
+ }
+ __ Set(output_reg, Immediate(0));
+ __ bind(&done);
}
--
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