Reviewers: ulan,
Message:
PTAL
Description:
Infer the range of XOR as limited by the highest possible changed bit.
Please review this at https://chromiumcodereview.appspot.com/16361003/
SVN Base: https://v8.googlecode.com/svn/branches/bleeding_edge
Affected files:
M src/hydrogen-instructions.cc
Index: src/hydrogen-instructions.cc
diff --git a/src/hydrogen-instructions.cc b/src/hydrogen-instructions.cc
index
3b18dab308b220f92fc33713f24249353ab75ef2..94b900227cf7cf5a33e7db48ca9cbdd681666233
100644
--- a/src/hydrogen-instructions.cc
+++ b/src/hydrogen-instructions.cc
@@ -2310,7 +2310,42 @@ 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()->range() != NULL && right()->range() != NULL) {
+ // 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();
+
+ // With the same number of bits, 1 lower value can be represented on
the
+ // negative side. Lower the number of required negative bits of log2
+ // values by removing this value.
+ if (left_upper < 0) left_upper = llabs(left_upper + 1);
+ if (left_lower < 0) left_lower = llabs(left_lower + 1);
+ if (right_upper < 0) right_upper = llabs(right_upper + 1);
+ if (right_lower < 0) right_lower = llabs(right_lower + 1);
+
+ // 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()
--
--
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