Revision: 20254
Author: [email protected]
Date: Tue Mar 25 16:09:29 2014 UTC
Log: Revert r20246 "ARM64: Add overflow checking support for
multiplications by constant powers of 2."
Reason: mjsunit/mul-exhaustive-part4 fails in no snaphot debug.
[email protected]
Review URL: https://codereview.chromium.org/211393002
http://code.google.com/p/v8/source/detail?r=20254
Modified:
/branches/bleeding_edge/src/arm64/lithium-arm64.cc
/branches/bleeding_edge/src/arm64/lithium-codegen-arm64.cc
=======================================
--- /branches/bleeding_edge/src/arm64/lithium-arm64.cc Tue Mar 25 13:35:19
2014 UTC
+++ /branches/bleeding_edge/src/arm64/lithium-arm64.cc Tue Mar 25 16:09:29
2014 UTC
@@ -1891,36 +1891,29 @@
HValue* least_const = instr->BetterLeftOperand();
HValue* most_const = instr->BetterRightOperand();
- LOperand* left;
+ LOperand* left = UseRegisterAtStart(least_const);
// LMulConstI can handle a subset of constants:
// With support for overflow detection:
// -1, 0, 1, 2
+ // Without support for overflow detection:
// 2^n, -(2^n)
- // Without support for overflow detection:
// 2^n + 1, -(2^n - 1)
if (most_const->IsConstant()) {
int32_t constant = HConstant::cast(most_const)->Integer32Value();
- bool small_constant = (constant >= -1) && (constant <= 2);
- bool end_range_constant = (constant <= -kMaxInt) || (constant ==
kMaxInt);
- int32_t constant_abs = Abs(constant);
+ int32_t constant_abs = (constant >= 0) ? constant : -constant;
- if (!end_range_constant &&
- (small_constant ||
- (IsPowerOf2(constant_abs)) ||
- (!can_overflow && (IsPowerOf2(constant_abs + 1) ||
- IsPowerOf2(constant_abs - 1))))) {
+ if (((constant >= -1) && (constant <= 2)) ||
+ (!can_overflow && (IsPowerOf2(constant_abs) ||
+ IsPowerOf2(constant_abs + 1) ||
+ IsPowerOf2(constant_abs - 1)))) {
LConstantOperand* right = UseConstant(most_const);
- bool need_register = IsPowerOf2(constant_abs) && !small_constant;
- left = need_register ? UseRegister(least_const)
- : UseRegisterAtStart(least_const);
LMulConstIS* mul = new(zone()) LMulConstIS(left, right);
if (needs_environment) AssignEnvironment(mul);
return DefineAsRegister(mul);
}
}
- left = UseRegisterAtStart(least_const);
// LMulI/S can handle all cases, but it requires that a register is
// allocated for the second operand.
LInstruction* result;
=======================================
--- /branches/bleeding_edge/src/arm64/lithium-codegen-arm64.cc Tue Mar 25
14:26:55 2014 UTC
+++ /branches/bleeding_edge/src/arm64/lithium-codegen-arm64.cc Tue Mar 25
16:09:29 2014 UTC
@@ -4253,7 +4253,6 @@
Register left =
is_smi ? ToRegister(instr->left()) : ToRegister32(instr->left()) ;
int32_t right = ToInteger32(instr->right());
- ASSERT((right > -kMaxInt) || (right < kMaxInt));
bool can_overflow = instr->hydrogen()->CheckFlag(HValue::kCanOverflow);
bool bailout_on_minus_zero =
@@ -4297,40 +4296,20 @@
}
break;
+ // All other cases cannot detect overflow, because it would probably
be no
+ // faster than using the smull method in LMulI.
+ // TODO(jbramley): Investigate this, and add overflow support if it
would
+ // be useful.
default:
+ ASSERT(!can_overflow);
+
// Multiplication by constant powers of two (and some related values)
// can be done efficiently with shifted operands.
- int32_t right_abs = Abs(right);
-
- if (IsPowerOf2(right_abs)) {
- int right_log2 = WhichPowerOf2(right_abs);
-
- if (can_overflow) {
- Register scratch = result;
- ASSERT(!AreAliased(scratch, left));
- __ Cls(scratch, left);
- __ Cmp(scratch, right_log2);
- DeoptimizeIf(lt, instr->environment());
- }
-
- if (right >= 0) {
+ if (right >= 0) {
+ if (IsPowerOf2(right)) {
// result = left << log2(right)
- __ Lsl(result, left, right_log2);
- } else {
- // result = -left << log2(-right)
- __ Neg(result, Operand(left, LSL, right_log2));
- }
- return;
- }
-
-
- // For the following cases, we could perform a conservative overflow
check
- // with CLS as above. However the few cycles saved are likely not
worth
- // the risk of deoptimizing more often than required.
- ASSERT(!can_overflow);
-
- if (right >= 0) {
- if (IsPowerOf2(right - 1)) {
+ __ Lsl(result, left, WhichPowerOf2(right));
+ } else if (IsPowerOf2(right - 1)) {
// result = left + left << log2(right - 1)
__ Add(result, left, Operand(left, LSL, WhichPowerOf2(right -
1)));
} else if (IsPowerOf2(right + 1)) {
@@ -4341,7 +4320,10 @@
UNREACHABLE();
}
} else {
- if (IsPowerOf2(-right + 1)) {
+ if (IsPowerOf2(-right)) {
+ // result = -left << log2(-right)
+ __ Neg(result, Operand(left, LSL, WhichPowerOf2(-right)));
+ } else if (IsPowerOf2(-right + 1)) {
// result = left - left << log2(-right + 1)
__ Sub(result, left, Operand(left, LSL, WhichPowerOf2(-right +
1)));
} else if (IsPowerOf2(-right - 1)) {
@@ -4352,6 +4334,7 @@
UNREACHABLE();
}
}
+ break;
}
}
--
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