Revision: 14933
Author: [email protected]
Date: Tue Jun 4 05:26:39 2013
Log: Infer the range of XOR as limited by the highest possible changed
bit.
[email protected]
Review URL: https://chromiumcodereview.appspot.com/16361003
http://code.google.com/p/v8/source/detail?r=14933
Modified:
/branches/bleeding_edge/src/hydrogen-instructions.cc
=======================================
--- /branches/bleeding_edge/src/hydrogen-instructions.cc Tue Jun 4
03:30:05 2013
+++ /branches/bleeding_edge/src/hydrogen-instructions.cc Tue Jun 4
05:26:39 2013
@@ -2310,7 +2310,39 @@
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()
--
--
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