https://chromiumcodereview.appspot.com/22935005/diff/1/src/x64/full-codegen-x64.cc
File src/x64/full-codegen-x64.cc (right):
https://chromiumcodereview.appspot.com/22935005/diff/1/src/x64/full-codegen-x64.cc#newcode4425
src/x64/full-codegen-x64.cc:4425: if (expr->op() == Token::INC) {
I think the shorter sequence is better without the scratch register in
the case that performance matters.
Have you considered making the SmiAddConstant/SmiSubConstant handle the
overflow case similarly to how this code does? e.g.
SmiAddConstant(...) {
addq(...)
Label local_done
j(no_overflow, &local_done);
subq(...)
jmp(&stub)
bind(&local_done);
}
Or do the extra branches destroy performance in this case?
Perhaps you should leave the "fast" version for now and we'll tackle
this problem in the CL that introduces the SmiWrapper
On 2013/08/13 09:05:57, haitao.feng wrote:
An alternative is:
if (expr->op() == Token::INC) {
__ SmiAddConstant(rax, rax, Smi::FromInt(1), &stub_call);
} else {
__ SmiSubConstant(rax, rax, Smi::FromInt(1), &stub_call);
}
__ jmp(&done, Label::kNear);
__ bind(&slow);
This version uses 5 instructions in SmiAddConstant (movq
kScratchRegister,
kSmiConstantRegister; addq(kScratchRegister, rax); j(overflow,
&stub_call);
movq(rax, kScratchRegister), jmp(&done)) than 2 (addq(rax,
kSmiConstantRegister), j(no_overflow, &done) for normal cases.
https://chromiumcodereview.appspot.com/22935005/
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