Reviewers: ulan,
Description:
A64: UseRegisterAtStart for rhs of LMulS
BUG=
Please review this at https://codereview.chromium.org/191283002/
SVN Base: https://v8.googlecode.com/svn/branches/bleeding_edge
Affected files (+21, -8 lines):
M src/a64/lithium-a64.cc
M src/a64/lithium-codegen-a64.cc
Index: src/a64/lithium-a64.cc
diff --git a/src/a64/lithium-a64.cc b/src/a64/lithium-a64.cc
index
12812bbf2e4f8b74928d0f56b4ad41b8981b670c..5d3d1eefda3e1459fd87b7ee341bff281ead037f
100644
--- a/src/a64/lithium-a64.cc
+++ b/src/a64/lithium-a64.cc
@@ -1849,8 +1849,7 @@ LInstruction* LChunkBuilder::DoMul(HMul* instr) {
// allocated for the second operand.
LInstruction* result;
if (instr->representation().IsSmi()) {
- // TODO(jbramley/rmcilroy): Fix LMulS so we can UseRegisterAtStart
here.
- LOperand* right = UseRegister(most_const);
+ LOperand* right = UseRegisterAtStart(most_const);
result = DefineAsRegister(new(zone()) LMulS(left, right));
} else {
LOperand* right = UseRegisterAtStart(most_const);
Index: src/a64/lithium-codegen-a64.cc
diff --git a/src/a64/lithium-codegen-a64.cc b/src/a64/lithium-codegen-a64.cc
index
8e443b9fb086bc82bec5593c1ddd79e87fddff5c..e7443ce99dcf1c51d7c5582c9bbc5395c9f3fddf
100644
--- a/src/a64/lithium-codegen-a64.cc
+++ b/src/a64/lithium-codegen-a64.cc
@@ -4232,7 +4232,7 @@ void LCodeGen::DoMulI(LMulI* instr) {
bool bailout_on_minus_zero =
instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero);
- if (bailout_on_minus_zero) {
+ if (bailout_on_minus_zero && !left.Is(right)) {
// If one operand is zero and the other is negative, the result is -0.
// - Set Z (eq) if either left or right, or both, are 0.
__ Cmp(left, 0);
@@ -4262,7 +4262,7 @@ void LCodeGen::DoMulS(LMulS* instr) {
bool bailout_on_minus_zero =
instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero);
- if (bailout_on_minus_zero) {
+ if (bailout_on_minus_zero && !left.Is(right)) {
// If one operand is zero and the other is negative, the result is -0.
// - Set Z (eq) if either left or right, or both, are 0.
__ Cmp(left, 0);
@@ -4280,10 +4280,24 @@ void LCodeGen::DoMulS(LMulS* instr) {
__ SmiTag(result);
DeoptimizeIf(ne, instr->environment());
} else {
- // TODO(jbramley): This could be rewritten to support
UseRegisterAtStart.
- ASSERT(!AreAliased(result, right));
- __ SmiUntag(result, left);
- __ Mul(result, result, right);
+ if (AreAliased(result, left, right)) {
+ // All three registers are the same: half untag the input and then
+ // multiply, giving a tagged result.
+ STATIC_ASSERT((kSmiShift % 2) == 0);
+ __ Asr(result, left, kSmiShift / 2);
+ __ Mul(result, result, result);
+ } else if (result.Is(left) && !left.Is(right)) {
+ // Registers result and left alias, right is distinct: untag left
into
+ // result, and then multiply by right, giving a tagged result.
+ __ SmiUntag(result, left);
+ __ Mul(result, result, right);
+ } else {
+ // Registers result and right alias, left is distinct, or all
registers
+ // are distinct: untag right into result, and then multiply by left,
+ // giving a tagged result.
+ __ SmiUntag(result, right);
+ __ Mul(result, left, result);
+ }
}
}
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