Reviewers: danno,
Message:
For the SmiSubConstant call-sites in the current src/:
code-stubs-x64.cc:2206: __ SmiSubConstant(r9, r9, Smi::FromInt(1));
full-codegen-x64.cc:4426: __ SmiSubConstant(rax, rax, Smi::FromInt(1));
full-codegen-x64.cc:4436: __ SmiSubConstant(rax, rax, Smi::FromInt(1));
ic-x64.cc:1178: __ SmiSubConstant(scratch2, scratch2, Smi::FromInt(2));
1) void SmiSubConstant(Register dst,
Register src,
Smi* constant,
Label* on_not_smi_result,
Label::Distance near_jump = Label::kFar);
is not used.
2) The overflow is checked at CountOperation
(https://codereview.chromium.org/22935005/).
I will continue working on 22935005 to tweak SmiSubConstants further.
Description:
Tweak SmiSubConstant for X64
Please review this at https://codereview.chromium.org/24986002/
SVN Base: https://v8.googlecode.com/svn/branches/bleeding_edge
Affected files (+9, -16 lines):
M src/x64/macro-assembler-x64.cc
Index: src/x64/macro-assembler-x64.cc
diff --git a/src/x64/macro-assembler-x64.cc b/src/x64/macro-assembler-x64.cc
index
96fa4fc49630424093eaa29874c118e95c34a115..bd1933e4f190e3ac59866886844eefcbe1d887fe
100644
--- a/src/x64/macro-assembler-x64.cc
+++ b/src/x64/macro-assembler-x64.cc
@@ -1584,20 +1584,14 @@ void MacroAssembler::SmiSubConstant(Register dst,
}
} else if (dst.is(src)) {
ASSERT(!dst.is(kScratchRegister));
- if (constant->value() == Smi::kMinValue) {
- // Subtracting min-value from any non-negative value will overflow.
- // We test the non-negativeness before doing the subtraction.
- testq(src, src);
- j(not_sign, on_not_smi_result, near_jump);
- LoadSmiConstant(kScratchRegister, constant);
- subq(dst, kScratchRegister);
- } else {
- // Subtract by adding the negation.
- LoadSmiConstant(kScratchRegister, Smi::FromInt(-constant->value()));
- addq(kScratchRegister, dst);
- j(overflow, on_not_smi_result, near_jump);
- movq(dst, kScratchRegister);
- }
+ Label done;
+ LoadSmiConstant(kScratchRegister, constant);
+ subq(dst, kScratchRegister);
+ j(no_overflow, &done, Label::kNear);
+ // Restore src.
+ addq(dst, kScratchRegister);
+ jmp(on_not_smi_result, near_jump);
+ bind(&done);
} else {
if (constant->value() == Smi::kMinValue) {
// Subtracting min-value from any non-negative value will overflow.
@@ -1605,8 +1599,7 @@ void MacroAssembler::SmiSubConstant(Register dst,
testq(src, src);
j(not_sign, on_not_smi_result, near_jump);
LoadSmiConstant(dst, constant);
- // Adding and subtracting the min-value gives the same result, it
only
- // differs on the overflow bit, which we don't check here.
+ // No overflow.
addq(dst, src);
} else {
// Subtract by adding the negation.
--
--
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