Fixing MathPowHalf on x64.

src/x64/lithium-codegen-x64.cc

Index: src/x64/lithium-codegen-x64.cc
diff --git a/src/x64/lithium-codegen-x64.cc b/src/x64/lithium-codegen-x64.cc
index ce2cddfab75791594aaef96e0fa9c3ffcf999da2..feedeeb1eed59eeafca2ee9dff15418cddf05364 100644
--- a/src/x64/lithium-codegen-x64.cc
+++ b/src/x64/lithium-codegen-x64.cc
@@ -2852,9 +2852,28 @@ void LCodeGen::DoMathPowHalf(LUnaryMathOperation* instr) {
   XMMRegister xmm_scratch = xmm0;
   XMMRegister input_reg = ToDoubleRegister(instr->InputAt(0));
   ASSERT(ToDoubleRegister(instr->result()).is(input_reg));
+
+  // Note that according to ECMA-262 15.8.2.13:
+  // Math.pow(-Infinity, 0.5) == Infinity
+  // Math.sqrt(-Infinity) == NaN
+  Label done, sqrt;
+  // Check base for -Infinity.  According to IEEE-754, single-precision

[ulan, 2011/12/05 16:32:41]

double-precision

+  // -Infinity has the highest 12 bits set and the lowest 52 bits cleared.
+  __ movq(kScratchRegister, V8_INT64_C(0xFFF0000000000000), RelocInfo::NONE);
+  __ movq(xmm_scratch, kScratchRegister);
+  __ ucomisd(xmm_scratch, input_reg);
+  __ j(not_equal, &sqrt, Label::kNear);
+  // If input is -Infinity, return Infinity.
+  __ xorps(input_reg, input_reg);
+  __ subsd(input_reg, xmm_scratch);
+  __ jmp(&done, Label::kNear);
+
+  // Square root.
+  __ bind(&sqrt);
   __ xorps(xmm_scratch, xmm_scratch);
   __ addsd(input_reg, xmm_scratch);  // Convert -0 to +0.
   __ sqrtsd(input_reg, input_reg);
+  __ bind(&done);
 }