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X64: Change overflow checks to only jump on overflow.

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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.

Review URL: http://codereview.chromium.org/2823004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4877 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
This commit is contained in:
lrn@chromium.org 2010-06-16 12:11:22 +00:00
parent 2581562248
commit 14b216bd61
1 changed files with 44 additions and 44 deletions
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88
src/x64/macro-assembler-x64.cc
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@ -696,15 +696,12 @@ void MacroAssembler::SmiAdd(Register dst,
movq(dst, src1);
addq(dst, src2);
}
Assert(no_overflow, "Smi addition onverflow");
Assert(no_overflow, "Smi addition overflow");
} else if (dst.is(src1)) {
addq(dst, src2);
Label smi_result;
j(no_overflow, &smi_result);
// Restore src1.
subq(src1, src2);
jmp(on_not_smi_result);
bind(&smi_result);
movq(kScratchRegister, src1);
addq(kScratchRegister, src2);
j(overflow, on_not_smi_result);
movq(dst, kScratchRegister);
} else {
movq(dst, src1);
addq(dst, src2);
@ -727,15 +724,11 @@ void MacroAssembler::SmiSub(Register dst,
movq(dst, src1);
subq(dst, src2);
}
Assert(no_overflow, "Smi substraction onverflow");
Assert(no_overflow, "Smi subtraction overflow");
} else if (dst.is(src1)) {
cmpq(dst, src2);
j(overflow, on_not_smi_result);
subq(dst, src2);
Label smi_result;
j(no_overflow, &smi_result);
// Restore src1.
addq(src1, src2);
jmp(on_not_smi_result);
bind(&smi_result);
} else {
movq(dst, src1);
subq(dst, src2);
@ -757,15 +750,12 @@ void MacroAssembler::SmiSub(Register dst,
movq(dst, src1);
subq(dst, src2);
}
Assert(no_overflow, "Smi substraction onverflow");
Assert(no_overflow, "Smi subtraction overflow");
} else if (dst.is(src1)) {
subq(dst, src2);
Label smi_result;
j(no_overflow, &smi_result);
// Restore src1.
addq(src1, src2);
jmp(on_not_smi_result);
bind(&smi_result);
movq(kScratchRegister, src1);
subq(kScratchRegister, src2);
j(overflow, on_not_smi_result);
movq(src1, kScratchRegister);
} else {
movq(dst, src1);
subq(dst, src2);
@ -883,12 +873,9 @@ void MacroAssembler::SmiAddConstant(Register dst,
ASSERT(!dst.is(kScratchRegister));
Move(kScratchRegister, constant);
addq(dst, kScratchRegister);
Label result_ok;
j(no_overflow, &result_ok);
subq(dst, kScratchRegister);
jmp(on_not_smi_result);
bind(&result_ok);
addq(kScratchRegister, dst);
j(overflow, on_not_smi_result);
movq(dst, kScratchRegister);
} else {
Move(dst, constant);
addq(dst, src);
@ -910,10 +897,12 @@ void MacroAssembler::SmiSubConstant(Register dst, Register src, Smi* constant) {
} else {
// Subtract by adding the negative, to do it in two operations.
if (constant->value() == Smi::kMinValue) {
Move(kScratchRegister, constant);
movq(dst, src);
subq(dst, kScratchRegister);
Move(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.
addq(dst, src);
} else {
// Subtract by adding the negation.
Move(dst, Smi::FromInt(-constant->value()));
addq(dst, src);
}
@ -931,21 +920,32 @@ void MacroAssembler::SmiSubConstant(Register dst,
}
} else if (dst.is(src)) {
ASSERT(!dst.is(kScratchRegister));
Move(kScratchRegister, constant);
subq(dst, kScratchRegister);
Label sub_success;
j(no_overflow, &sub_success);
addq(src, kScratchRegister);
jmp(on_not_smi_result);
bind(&sub_success);
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);
Move(kScratchRegister, constant);
subq(dst, kScratchRegister);
} else {
// Subtract by adding the negation.
Move(kScratchRegister, Smi::FromInt(-constant->value()));
addq(kScratchRegister, dst);
j(overflow, on_not_smi_result);
movq(dst, kScratchRegister);
}
} else {
if (constant->value() == Smi::kMinValue) {
Move(kScratchRegister, constant);
movq(dst, src);
subq(dst, kScratchRegister);
j(overflow, on_not_smi_result);
// 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);
Move(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.
addq(dst, src);
} else {
// Subtract by adding the negation.
Move(dst, Smi::FromInt(-(constant->value())));
addq(dst, src);
j(overflow, on_not_smi_result);