Revision: 4877
Author: [email protected]
Date: Wed Jun 16 05:11:22 2010
Log: 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.
Review URL: http://codereview.chromium.org/2823004
http://code.google.com/p/v8/source/detail?r=4877
Modified:
/branches/bleeding_edge/src/x64/macro-assembler-x64.cc
=======================================
--- /branches/bleeding_edge/src/x64/macro-assembler-x64.cc Fri May 28
01:37:44 2010
+++ /branches/bleeding_edge/src/x64/macro-assembler-x64.cc Wed Jun 16
05:11:22 2010
@@ -696,15 +696,12 @@
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 @@
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 @@
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 @@
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 @@
} 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 @@
}
} 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);
- } else {
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);
- movq(dst, src);
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) {
+ // 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);
--
v8-dev mailing list
[email protected]
http://groups.google.com/group/v8-dev
