JDK-8203628 : Optimize (masked) byte memory comparisons on x86
- Type: Enhancement
- Component: hotspot
- Sub-Component: compiler
- Affected Version: 11
- Priority: P4
- Status: Resolved
- Resolution: Fixed
- CPU: x86
- Submitted: 2018-05-22
- Updated: 2018-06-07
- Resolved: 2018-05-28
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| JDK 11 |
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11 b16Fixed  |
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Description
We found this during Shenandoah performance work. In GC barriers fastpath, we have the shape like (Set cr (CmpI (AndI (LoadUB op1) op2) opZ)), which compiles down to: mov $op2, %r1 andb ($op1), %r1 test %r1, %r1 ...while it can be compiled to just: testb ($op1), $op2 ...thus saving the %r1. G1 SATB checks have similar shape, but without the mask, and they waste the register in the same way.
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