Tweaks on Math.pow (ia32 and x64).

Tweaks on Math.pow (ia32 and x64).

Committed: http://code.google.com/p/v8/source/detail?r=10203

[Yang, 2011-12-07 15:07:50]

Please take a look.

I removed the double_int_runtime bail out since this would only be used when we
encounter potential subnormals in the int_exponent case. Instead we just bail
out to power_double_double.

I also cleared up the runtime functions to better mirror the generated code.

http://codereview.chromium.org/8831008/diff/1/src/ia32/code-stubs-ia32.cc
File src/ia32/code-stubs-ia32.cc (left):

http://codereview.chromium.org/8831008/diff/1/src/ia32/code-stubs-ia32.cc#old...
src/ia32/code-stubs-ia32.cc:3135: __ and_(exponent,
Immediate(kClearSignBitMask));
This is a screw-up I did earlier. Obviously this code does not result in
absolute, but triggered a bail out, which is why this mistake made no visible
difference.

http://codereview.chromium.org/8831008/diff/1/src/x64/code-stubs-x64.cc
File src/x64/code-stubs-x64.cc (left):

http://codereview.chromium.org/8831008/diff/1/src/x64/code-stubs-x64.cc#oldco...
src/x64/code-stubs-x64.cc:2186: __ andl(scratch, Immediate(kClearSignBitMask));
Ditto in ia32.

[ulan, 2011-12-07 16:03:04]

LGTM with comments.

http://codereview.chromium.org/8831008/diff/1/src/runtime.cc
File src/runtime.cc (right):

http://codereview.chromium.org/8831008/diff/1/src/runtime.cc#newcode7444
src/runtime.cc:7444: } else if (isnan(y) || ((x == 1 || x == -1) && isinf(y))) {
This code is almost the same as in power_double_double. Can we reuse it?

http://codereview.chromium.org/8831008/diff/1/src/x64/code-stubs-x64.cc
File src/x64/code-stubs-x64.cc (right):

http://codereview.chromium.org/8831008/diff/1/src/x64/code-stubs-x64.cc#newco...
src/x64/code-stubs-x64.cc:2208: __ cvtlsi2sd(double_exponent, exponent);
Could you please add a comment explaining why we need the instruction?

1) double_exponent is aliased with double_scratch2, so it gets overwritten.
2) double_exponent might not contain the exponent at all if the exponent is SMI.

http://codereview.chromium.org/8831008/diff/1/src/x64/code-stubs-x64.cc#newco...
src/x64/code-stubs-x64.cc:2234: };
Redundant semicolon.