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MIPS: Re-work DoModI.

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Changes:
-separated the two code-paths (constant power of 2 divisor similar to ARM and everything else)
-replaced a bailout condition with faster handling (negative modulo result)
-removed a possibly useless mov instruction from one path
-replaced the IsConstantOperand condition with the more meaningful HasPowerOf2Divisor (although in this specific case they're equivalent)

BUG=
TEST=

Review URL: http://codereview.chromium.org/8591002
Patch from Gergely Kis <gergely@homejinni.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10016 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
This commit is contained in:
danno@chromium.org 2011-11-17 13:33:56 +00:00
parent e99b92723d
commit bef75b3496
1 changed files with 37 additions and 42 deletions
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79
src/mips/lithium-codegen-mips.cc
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@ -874,52 +874,47 @@ void LCodeGen::DoModI(LModI* instr) {
const Register left = ToRegister(instr->InputAt(0));
const Register result = ToRegister(instr->result());
// p2constant holds the right side value if it's a power of 2 constant.
// In other cases it is 0.
int32_t p2constant = 0;
Label done;
if (instr->InputAt(1)->IsConstantOperand()) {
p2constant = ToInteger32(LConstantOperand::cast(instr->InputAt(1)));
if (p2constant % 2 != 0) {
p2constant = 0;
}
// Result always takes the sign of the dividend (left).
p2constant = abs(p2constant);
}
// div runs in the background while we check for special cases.
Register right = EmitLoadRegister(instr->InputAt(1), scratch);
__ div(left, right);
// Check for x % 0.
if (instr->hydrogen()->CheckFlag(HValue::kCanBeDivByZero)) {
DeoptimizeIf(eq, instr->environment(), right, Operand(zero_reg));
}
Label skip_div, do_div;
if (p2constant != 0) {
// Fall back to the result of the div instruction if we could have sign
// problems.
__ Branch(&do_div, lt, left, Operand(zero_reg));
// Modulo by masking.
__ And(scratch, left, p2constant - 1);
__ Branch(&skip_div);
}
__ bind(&do_div);
__ mfhi(scratch);
__ bind(&skip_div);
if (instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero)) {
if (instr->hydrogen()->HasPowerOf2Divisor()) {
Register scratch = scratch0();
ASSERT(!left.is(scratch));
__ mov(scratch, left);
int32_t p2constant = HConstant::cast(
instr->hydrogen()->right())->Integer32Value();
ASSERT(p2constant != 0);
// Result always takes the sign of the dividend (left).
Label done;
__ Branch(USE_DELAY_SLOT, &done, ge, left, Operand(zero_reg));
__ mov(result, scratch);
DeoptimizeIf(eq, instr->environment(), result, Operand(zero_reg));
__ bind(&done);
p2constant = abs(p2constant);
Label positive_dividend;
__ Branch(USE_DELAY_SLOT, &positive_dividend, ge, left, Operand(zero_reg));
__ subu(result, zero_reg, left);
__ And(result, result, p2constant - 1);
if (instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero)) {
DeoptimizeIf(eq, instr->environment(), result, Operand(zero_reg));
}
__ Branch(USE_DELAY_SLOT, &done);
__ subu(result, zero_reg, result);
__ bind(&positive_dividend);
__ And(result, scratch, p2constant - 1);
} else {
__ Move(result, scratch);
// div runs in the background while we check for special cases.
Register right = EmitLoadRegister(instr->InputAt(1), scratch);
__ div(left, right);
// Check for x % 0.
if (instr->hydrogen()->CheckFlag(HValue::kCanBeDivByZero)) {
DeoptimizeIf(eq, instr->environment(), right, Operand(zero_reg));
}
__ Branch(USE_DELAY_SLOT, &done, ge, left, Operand(zero_reg));
__ mfhi(result);
if (instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero)) {
DeoptimizeIf(eq, instr->environment(), result, Operand(zero_reg));
}
}
__ bind(&done);
}