X64: Change overflow checks to only jump on overflow.

X64: Change overflow checks to only jump on overflow. 
Costs an extra move because the result is calculated in a scratch register 
and only moved to destination on non-overflow in order to preserve source 
registers in case of overflow.

Committed as revision 4877.

[Lasse Reichstein, 2010-06-15 13:00:01]

Small review.

[William Hesse, 2010-06-15 13:53:19]

LGTM.

http://codereview.chromium.org/2823004/diff/1/2
File src/x64/macro-assembler-x64.cc (right):

http://codereview.chromium.org/2823004/diff/1/2#newcode699
src/x64/macro-assembler-x64.cc:699: Assert(no_overflow, "Smi addition
onverflow");
overflow

http://codereview.chromium.org/2823004/diff/1/2#newcode728
src/x64/macro-assembler-x64.cc:728: Assert(no_overflow, "Smi substraction
onverflow");
subtraction overflow

http://codereview.chromium.org/2823004/diff/1/2#newcode755
src/x64/macro-assembler-x64.cc:755: Assert(no_overflow, "Smi substraction
onverflow");
Smi subtraction overflow

http://codereview.chromium.org/2823004/diff/1/2#newcode925
src/x64/macro-assembler-x64.cc:925: j(positive, on_not_smi_result);
positive or zero give overflow.

http://codereview.chromium.org/2823004/diff/1/2#newcode937
src/x64/macro-assembler-x64.cc:937: j(positive, on_not_smi_result);
positive or zero

http://codereview.chromium.org/2823004/diff/1/2#newcode939
src/x64/macro-assembler-x64.cc:939: addq(dst, src);  // Adding and subtracting
the min-value is the same.
Adding or subtracting the min-value is the same, aside from the overflow flag.

[Lasse Reichstein, 2010-06-16 08:20:18]

Fixed typos, added comments, changed "positive" to "not_sign" (and added
comment). Reduced one case by one instruction to make it match the similar
cases.