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Infer the range of XOR as limited by the highest possible changed bit.

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R=ulan@chromium.org

Review URL: https://chromiumcodereview.appspot.com/16361003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@14933 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
This commit is contained in:
verwaest@chromium.org 2013-06-04 12:26:39 +00:00
parent 106a477443
commit 277ec5d7b2
1 changed files with 33 additions and 1 deletions
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34
src/hydrogen-instructions.cc
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@ -2310,7 +2310,39 @@ void HMathMinMax::InferRepresentation(HInferRepresentation* h_infer) {
Range* HBitwise::InferRange(Zone* zone) {
if (op() == Token::BIT_XOR) return HValue::InferRange(zone);
if (op() == Token::BIT_XOR) {
if (left()->HasRange() && right()->HasRange()) {
// The maximum value has the high bit, and all bits below, set:
// (1 << high) - 1.
// If the range can be negative, the minimum int is a negative number with
// the high bit, and all bits below, unset:
// -(1 << high).
// If it cannot be negative, conservatively choose 0 as minimum int.
int64_t left_upper = left()->range()->upper();
int64_t left_lower = left()->range()->lower();
int64_t right_upper = right()->range()->upper();
int64_t right_lower = right()->range()->lower();
if (left_upper < 0) left_upper = ~left_upper;
if (left_lower < 0) left_lower = ~left_lower;
if (right_upper < 0) right_upper = ~right_upper;
if (right_lower < 0) right_lower = ~right_lower;
// Find the highest used bit.
int high = static_cast<int>(log2(left_upper));
high = Max(high, static_cast<int>(log2(left_lower)));
high = Max(high, static_cast<int>(log2(right_upper)));
high = Max(high, static_cast<int>(log2(right_lower)));
int64_t limit = 1;
limit <<= high + 1;
int32_t min = (left()->range()->CanBeNegative() ||
right()->range()->CanBeNegative())
? static_cast<int32_t>(-limit) : 0;
return new(zone) Range(min, static_cast<int32_t>(limit - 1));
}
return HValue::InferRange(zone);
}
const int32_t kDefaultMask = static_cast<int32_t>(0xffffffff);
int32_t left_mask = (left()->range() != NULL)
? left()->range()->Mask()