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Optimize constant divisions by powers of 2.

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Review URL: http://codereview.chromium.org/126116

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2164 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
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erik.corry@gmail.com 2009-06-15 10:27:52 +00:00
parent f36f5f2331
commit e44d30e284
1 changed files with 15 additions and 0 deletions
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15
src/parser.cc
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@ -2647,6 +2647,21 @@ Expression* Parser::ParseBinaryExpression(int prec, bool accept_IN, bool* ok) {
}
}
// Convert constant divisions to multiplications for speed.
if (op == Token::DIV &&
y && y->AsLiteral() && y->AsLiteral()->handle()->IsNumber()) {
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)) {
y = NewNumberLiteral(1 / y_val);
op = Token::MUL;
}
}
// For now we distinguish between comparisons and other binary
// operations. (We could combine the two and get rid of this
// code an AST node eventually.)