Author: [email protected]
Date: Wed Jun 17 12:26:01 2009
New Revision: 2212
Modified:
branches/bleeding_edge/src/parser.cc
Log:
Don't strength reduce divisions by 1 or 2 as they can often be
handled by an optimistic inline idiv.
Review URL: http://codereview.chromium.org/125258
Modified: branches/bleeding_edge/src/parser.cc
==============================================================================
--- branches/bleeding_edge/src/parser.cc (original)
+++ branches/bleeding_edge/src/parser.cc Wed Jun 17 12:26:01 2009
@@ -2653,10 +2653,15 @@
double y_val = y->AsLiteral()->handle()->Number();
int64_t y_int = static_cast<int64_t>(y_val);
// There are rounding issues with this optimization, but they don't
- // apply if the number to be divided with has a reciprocal that can
- // be precisely represented as a floating point number. This is
- // the case if the number is an integer power of 2.
- if (static_cast<double>(y_int) == y_val && IsPowerOf2(y_int)) {
+ // apply if the number to be divided with has a reciprocal that
can be
+ // precisely represented as a floating point number. This is the
case
+ // if the number is an integer power of 2. Negative integer
powers of
+ // 2 work too, but for -2, -1, 1 and 2 we don't do the strength
+ // reduction because the inlined optimistic idiv has a reasonable
+ // chance of succeeding by producing a Smi answer with no
remainder.
+ if (static_cast<double>(y_int) == y_val &&
+ (IsPowerOf2(y_int) || IsPowerOf2(-y_int)) &&
+ (y_int > 2 || y_int < -2)) {
y = NewNumberLiteral(1 / y_val);
op = Token::MUL;
}
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