Mercurial > jdk8-mips64-public > hotspot / file comparison
comparison: src/share/vm/opto/compile.cpp
src/share/vm/opto/compile.cpp
- changeset 4691
- 571076d3c79d
- parent 4589
- 8b3da8d14c93
- child 4694
- 8651f608fea4
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| 4689:bf06968a8a00 | 4691:571076d3c79d |
|---|---|
| 3667 // Clear control input and let IGVN optimize expensive nodes if | 3667 // Clear control input and let IGVN optimize expensive nodes if |
| 3668 // OptimizeExpensiveOps is off. | 3668 // OptimizeExpensiveOps is off. |
| 3669 n->set_req(0, NULL); | 3669 n->set_req(0, NULL); |
| 3670 } | 3670 } |
| 3671 } | 3671 } |
| 3672 | |
| 3673 // Auxiliary method to support randomized stressing/fuzzing. | |
| 3674 // | |
| 3675 // This method can be called the arbitrary number of times, with current count | |
| 3676 // as the argument. The logic allows selecting a single candidate from the | |
| 3677 // running list of candidates as follows: | |
| 3678 // int count = 0; | |
| 3679 // Cand* selected = null; | |
| 3680 // while(cand = cand->next()) { | |
| 3681 // if (randomized_select(++count)) { | |
| 3682 // selected = cand; | |
| 3683 // } | |
| 3684 // } | |
| 3685 // | |
| 3686 // Including count equalizes the chances any candidate is "selected". | |
| 3687 // This is useful when we don't have the complete list of candidates to choose | |
| 3688 // from uniformly. In this case, we need to adjust the randomicity of the | |
| 3689 // selection, or else we will end up biasing the selection towards the latter | |
| 3690 // candidates. | |
| 3691 // | |
| 3692 // Quick back-envelope calculation shows that for the list of n candidates | |
| 3693 // the equal probability for the candidate to persist as "best" can be | |
| 3694 // achieved by replacing it with "next" k-th candidate with the probability | |
| 3695 // of 1/k. It can be easily shown that by the end of the run, the | |
| 3696 // probability for any candidate is converged to 1/n, thus giving the | |
| 3697 // uniform distribution among all the candidates. | |
| 3698 // | |
| 3699 // We don't care about the domain size as long as (RANDOMIZED_DOMAIN / count) is large. | |
| 3700 #define RANDOMIZED_DOMAIN_POW 29 | |
| 3701 #define RANDOMIZED_DOMAIN (1 << RANDOMIZED_DOMAIN_POW) | |
| 3702 #define RANDOMIZED_DOMAIN_MASK ((1 << (RANDOMIZED_DOMAIN_POW + 1)) - 1) | |
| 3703 bool Compile::randomized_select(int count) { | |
| 3704 assert(count > 0, "only positive"); | |
| 3705 return (os::random() & RANDOMIZED_DOMAIN_MASK) < (RANDOMIZED_DOMAIN / count); | |
| 3706 } |
