Revision: 4391
Author: [email protected]
Date: Mon Apr 12 08:05:55 2010
Log: Faster comparison of identical objects.
Review URL: http://codereview.chromium.org/1558040
http://code.google.com/p/v8/source/detail?r=4391
Modified:
/branches/bleeding_edge/src/ia32/codegen-ia32.cc
=======================================
--- /branches/bleeding_edge/src/ia32/codegen-ia32.cc Mon Apr 12 03:07:50
2010
+++ /branches/bleeding_edge/src/ia32/codegen-ia32.cc Mon Apr 12 08:05:55
2010
@@ -11080,6 +11080,14 @@
masm->RecordWriteHelper(object_, addr_, scratch_);
masm->ret(0);
}
+
+
+static int NegativeComparisonResult(Condition cc) {
+ ASSERT(cc != equal);
+ ASSERT((cc == less) || (cc == less_equal)
+ || (cc == greater) || (cc == greater_equal));
+ return (cc == greater || cc == greater_equal) ? LESS : GREATER;
+}
void CompareStub::Generate(MacroAssembler* masm) {
@@ -11088,55 +11096,79 @@
// NOTICE! This code is only reached after a smi-fast-case check, so
// it is certain that at least one operand isn't a smi.
- if (cc_ == equal) { // Both strict and non-strict.
- Label slow; // Fallthrough label.
- // Equality is almost reflexive (everything but NaN), so start by
testing
- // for "identity and not NaN".
- {
- Label not_identical;
- __ cmp(eax, Operand(edx));
- __ j(not_equal, ¬_identical);
- // Test for NaN. Sadly, we can't just compare to
Factory::nan_value(),
- // so we do the second best thing - test it ourselves.
-
- if (never_nan_nan_) {
- __ Set(eax, Immediate(0));
- __ ret(0);
- } else {
- Label return_equal;
- Label heap_number;
- // If it's not a heap number, then return equal.
- __ cmp(FieldOperand(edx, HeapObject::kMapOffset),
- Immediate(Factory::heap_number_map()));
- __ j(equal, &heap_number);
- __ bind(&return_equal);
- __ Set(eax, Immediate(0));
- __ ret(0);
-
- __ bind(&heap_number);
- // It is a heap number, so return non-equal if it's NaN and equal
if
- // it's not NaN.
- // The representation of NaN values has all exponent bits (52..62)
set,
- // and not all mantissa bits (0..51) clear.
- // We only accept QNaNs, which have bit 51 set.
- // Read top bits of double representation (second word of value).
-
- // Value is a QNaN if value & kQuietNaNMask == kQuietNaNMask, i.e.,
- // all bits in the mask are set. We only need to check the word
- // that contains the exponent and high bit of the mantissa.
- ASSERT_NE(0, (kQuietNaNHighBitsMask << 1) & 0x80000000u);
- __ mov(edx, FieldOperand(edx, HeapNumber::kExponentOffset));
- __ xor_(eax, Operand(eax));
- // Shift value and mask so kQuietNaNHighBitsMask applies to topmost
- // bits.
- __ add(edx, Operand(edx));
- __ cmp(edx, kQuietNaNHighBitsMask << 1);
+ // Identical objects can be compared fast, but there are some tricky
cases
+ // for NaN and undefined.
+ {
+ Label not_identical;
+ __ cmp(eax, Operand(edx));
+ __ j(not_equal, ¬_identical);
+
+ if (cc_ != equal) {
+ // Check for undefined. undefined OP undefined is false even though
+ // undefined == undefined.
+ Label check_for_nan;
+ __ cmp(edx, Factory::undefined_value());
+ __ j(not_equal, &check_for_nan);
+ __ Set(eax, Immediate(Smi::FromInt(NegativeComparisonResult(cc_))));
+ __ ret(0);
+ __ bind(&check_for_nan);
+ }
+
+ // Test for NaN. Sadly, we can't just compare to Factory::nan_value(),
+ // so we do the second best thing - test it ourselves.
+ // Note: if cc_ != equal, never_nan_nan_ is not used.
+ if (never_nan_nan_ && (cc_ == equal)) {
+ __ Set(eax, Immediate(Smi::FromInt(EQUAL)));
+ __ ret(0);
+ } else {
+ Label return_equal;
+ Label heap_number;
+ // If it's not a heap number, then return equal.
+ __ cmp(FieldOperand(edx, HeapObject::kMapOffset),
+ Immediate(Factory::heap_number_map()));
+ __ j(equal, &heap_number);
+ __ bind(&return_equal);
+ __ Set(eax, Immediate(Smi::FromInt(EQUAL)));
+ __ ret(0);
+
+ __ bind(&heap_number);
+ // It is a heap number, so return non-equal if it's NaN and equal if
+ // it's not NaN.
+ // The representation of NaN values has all exponent bits (52..62)
set,
+ // and not all mantissa bits (0..51) clear.
+ // We only accept QNaNs, which have bit 51 set.
+ // Read top bits of double representation (second word of value).
+
+ // Value is a QNaN if value & kQuietNaNMask == kQuietNaNMask, i.e.,
+ // all bits in the mask are set. We only need to check the word
+ // that contains the exponent and high bit of the mantissa.
+ ASSERT_NE(0, (kQuietNaNHighBitsMask << 1) & 0x80000000u);
+ __ mov(edx, FieldOperand(edx, HeapNumber::kExponentOffset));
+ __ xor_(eax, Operand(eax));
+ // Shift value and mask so kQuietNaNHighBitsMask applies to topmost
+ // bits.
+ __ add(edx, Operand(edx));
+ __ cmp(edx, kQuietNaNHighBitsMask << 1);
+ if (cc_ == equal) {
+ ASSERT_NE(1, EQUAL);
__ setcc(above_equal, eax);
__ ret(0);
- }
-
- __ bind(¬_identical);
- }
+ } else {
+ Label nan;
+ __ j(above_equal, &nan);
+ __ Set(eax, Immediate(Smi::FromInt(EQUAL)));
+ __ ret(0);
+ __ bind(&nan);
+ __ Set(eax,
Immediate(Smi::FromInt(NegativeComparisonResult(cc_))));
+ __ ret(0);
+ }
+ }
+
+ __ bind(¬_identical);
+ }
+
+ if (cc_ == equal) { // Both strict and non-strict.
+ Label slow; // Fallthrough label.
// If we're doing a strict equality comparison, we don't have to do
// type conversion, so we generate code to do fast comparison for
objects
@@ -11327,14 +11359,7 @@
builtin = strict_ ? Builtins::STRICT_EQUALS : Builtins::EQUALS;
} else {
builtin = Builtins::COMPARE;
- int ncr; // NaN compare result
- if (cc_ == less || cc_ == less_equal) {
- ncr = GREATER;
- } else {
- ASSERT(cc_ == greater || cc_ == greater_equal); // remaining cases
- ncr = LESS;
- }
- __ push(Immediate(Smi::FromInt(ncr)));
+ __ push(Immediate(Smi::FromInt(NegativeComparisonResult(cc_))));
}
// Restore return address on the stack.
--
v8-dev mailing list
[email protected]
http://groups.google.com/group/v8-dev
To unsubscribe, reply using "remove me" as the subject.
