Reviewers: danno, Sven Panne, Paul Lind, kisg, palfia, dusmil,
Description:
MIPS: Fixed flooring division by -1.
Port r20544 (a64196c)
Original commit message:
We should avoid ASR #0 on ARM. Simplified and improved code a bit
while we're there on all platforms. Human brains are very bad at
understanding nested structures...
BUG=v8:3259
LOG=y
Please review this at https://codereview.chromium.org/227583003/
SVN Base: https://github.com/v8/v8.git@gbl
Affected files (+19, -17 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
89620d8702e4969bda23bed7c772b33f4fe664d1..7c3f28f1615c98edf721ccdbe82d6b15f8b2f41a
100644
--- a/src/mips/lithium-codegen-mips.cc
+++ b/src/mips/lithium-codegen-mips.cc
@@ -1322,25 +1322,27 @@ void
LCodeGen::DoFlooringDivByPowerOf2I(LFlooringDivByPowerOf2I* instr) {
if (instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero)) {
DeoptimizeIf(eq, instr->environment(), result, Operand(zero_reg));
}
- if (instr->hydrogen()->CheckFlag(HValue::kLeftCanBeMinInt)) {
- // Note that we could emit branch-free code, but that would need one
more
- // register.
- __ Xor(at, scratch, result);
- if (divisor == -1) {
- DeoptimizeIf(ge, instr->environment(), at, Operand(zero_reg));
- __ sra(result, dividend, shift);
- } else {
- Label no_overflow, done;
- __ Branch(&no_overflow, lt, at, Operand(zero_reg));
- __ li(result, Operand(kMinInt / divisor));
- __ Branch(&done);
- __ bind(&no_overflow);
- __ sra(result, dividend, shift);
- __ bind(&done);
- }
- } else {
+
+ // 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));
+ return;
}
+
+ Label no_overflow, done;
+ __ Branch(&no_overflow, lt, at, Operand(zero_reg));
+ __ li(result, Operand(kMinInt / divisor));
+ __ Branch(&done);
+ __ bind(&no_overflow);
+ __ sra(result, dividend, shift);
+ __ bind(&done);
}
--
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