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Skip check for +/-0.5 in optimized Math.pow (ia32).

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Review URL: http://codereview.chromium.org/8820007

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10168 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
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yangguo@chromium.org 2011-12-06 09:20:28 +00:00
parent fe2049fcb8
commit 5e432754b3
1 changed files with 35 additions and 30 deletions
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65
src/ia32/code-stubs-ia32.cc
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@ -3025,38 +3025,43 @@ void MathPowStub::Generate(MacroAssembler* masm) {
__ ucomisd(xmm2, xmm4);
__ j(equal, &int_exponent);
// Detect square root case.
// Test for -0.5.
// Load xmm4 with -0.5.
__ mov(ecx, Immediate(0xBF000000u));
__ movd(xmm4, ecx);
__ cvtss2sd(xmm4, xmm4);
// xmm3 now has -0.5.
__ ucomisd(xmm4, xmm2);
__ j(not_equal, &not_minus_half, Label::kNear);
if (exponent_type_ == ON_STACK) {
// Detect square root case. Crankshaft detects constant +/-0.5 at
// compile time and uses DoMathPowHalf instead. We then skip this check
// for non-constant cases of +/-0.5 as these hardly occur.
// Calculates reciprocal of square root.eax
// sqrtsd returns -0 when input is -0. ECMA spec requires +0.
__ xorps(xmm2, xmm2);
__ addsd(xmm2, xmm1);
__ sqrtsd(xmm2, xmm2);
__ divsd(xmm3, xmm2);
__ jmp(&done);
// Test for -0.5.
// Load xmm4 with -0.5.
__ mov(ecx, Immediate(0xBF000000u));
__ movd(xmm4, ecx);
__ cvtss2sd(xmm4, xmm4);
// xmm3 now has -0.5.
__ ucomisd(xmm4, xmm2);
__ j(not_equal, &not_minus_half, Label::kNear);
// Test for 0.5.
__ bind(&not_minus_half);
// Load xmm2 with 0.5.
// Since xmm3 is 1 and xmm4 is -0.5 this is simply xmm4 + xmm3.
__ addsd(xmm4, xmm3);
// xmm2 now has 0.5.
__ ucomisd(xmm4, xmm2);
__ j(not_equal, &fast_power, Label::kNear);
// Calculates square root.
// sqrtsd returns -0 when input is -0. ECMA spec requires +0.
__ xorps(xmm4, xmm4);
__ addsd(xmm4, xmm1);
__ sqrtsd(xmm3, xmm4);
__ jmp(&done);
// Calculates reciprocal of square root.eax
// sqrtsd returns -0 when input is -0. ECMA spec requires +0.
__ xorps(xmm2, xmm2);
__ addsd(xmm2, xmm1);
__ sqrtsd(xmm2, xmm2);
__ divsd(xmm3, xmm2);
__ jmp(&done);
// Test for 0.5.
__ bind(&not_minus_half);
// Load xmm2 with 0.5.
// Since xmm3 is 1 and xmm4 is -0.5 this is simply xmm4 + xmm3.
__ addsd(xmm4, xmm3);
// xmm2 now has 0.5.
__ ucomisd(xmm4, xmm2);
__ j(not_equal, &fast_power, Label::kNear);
// Calculates square root.
// sqrtsd returns -0 when input is -0. ECMA spec requires +0.
__ xorps(xmm4, xmm4);
__ addsd(xmm4, xmm1);
__ sqrtsd(xmm3, xmm4);
__ jmp(&done);
}
// Using FPU instructions to calculate power.
Label fast_power_failed;