Reviewers: danno, Sven Panne, Paul Lind, kisg, palfia, dusmil,
Description:
MIPS: Fixed flooring division by a power of 2, once again...
Port r21769 (52e191b)
Original commit message:
Avoid right shifts by zero bits: On ARM it actually means shifting by
32 bits (correctness issue) and on other platforms they are useless
(performance issue). This is fix for the fix in r20544.
BUG=v8:3259
LOG=y
Please review this at https://codereview.chromium.org/322403006/
SVN Base: https://github.com/v8/v8.git@gbl
Affected files (+14, -10 lines):
M src/mips/lithium-codegen-mips.cc
Index: src/mips/lithium-codegen-mips.cc
diff --git a/src/mips/lithium-codegen-mips.cc
b/src/mips/lithium-codegen-mips.cc
index
65fe1aa910f1243650e64e761524d9a8b7ede4da..1b2dec04416480659edd618642d88277ccfef9a6
100644
--- a/src/mips/lithium-codegen-mips.cc
+++ b/src/mips/lithium-codegen-mips.cc
@@ -1309,8 +1309,8 @@ void
LCodeGen::DoFlooringDivByPowerOf2I(LFlooringDivByPowerOf2I* instr) {
Register dividend = ToRegister(instr->dividend());
Register result = ToRegister(instr->result());
int32_t divisor = instr->divisor();
- Register scratch = scratch0();
- ASSERT(!scratch.is(dividend));
+ Register scratch = result.is(dividend) ? scratch0() : dividend;
+ ASSERT(!result.is(dividend) || !scratch.is(dividend));
// If the divisor is 1, return the dividend.
if (divisor == 1) {
@@ -1328,6 +1328,8 @@ void
LCodeGen::DoFlooringDivByPowerOf2I(LFlooringDivByPowerOf2I* instr) {
// If the divisor is negative, we have to negate and handle edge cases.
if (instr->hydrogen()->CheckFlag(HValue::kLeftCanBeMinInt)) {
+ // divident can be the same register as result so save the value of it
+ // for checking overflow.
__ Move(scratch, dividend);
}
__ Subu(result, zero_reg, dividend);
@@ -1335,16 +1337,18 @@ void
LCodeGen::DoFlooringDivByPowerOf2I(LFlooringDivByPowerOf2I* instr) {
DeoptimizeIf(eq, instr->environment(), result, Operand(zero_reg));
}
- // If the negation could not overflow, simply shifting is OK.
- if (!instr->hydrogen()->CheckFlag(HValue::kLeftCanBeMinInt)) {
- __ sra(result, dividend, shift);
- return;
- }
-
// Dividing by -1 is basically negation, unless we overflow.
__ Xor(at, scratch, result);
if (divisor == -1) {
- DeoptimizeIf(ge, instr->environment(), at, Operand(zero_reg));
+ if (instr->hydrogen()->CheckFlag(HValue::kLeftCanBeMinInt)) {
+ DeoptimizeIf(ge, instr->environment(), at, Operand(zero_reg));
+ }
+ return;
+ }
+
+ // If the negation could not overflow, simply shifting is OK.
+ if (!instr->hydrogen()->CheckFlag(HValue::kLeftCanBeMinInt)) {
+ __ sra(result, result, shift);
return;
}
@@ -1353,7 +1357,7 @@ void
LCodeGen::DoFlooringDivByPowerOf2I(LFlooringDivByPowerOf2I* instr) {
__ li(result, Operand(kMinInt / divisor));
__ Branch(&done);
__ bind(&no_overflow);
- __ sra(result, dividend, shift);
+ __ sra(result, result, shift);
__ bind(&done);
}
--
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