Revert multiply to use non-intrinsic exactness checks#8523
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headius merged 1 commit intojruby:masterfrom Jan 10, 2025
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Revert multiply to use non-intrinsic exactness checks#8523headius merged 1 commit intojruby:masterfrom
headius merged 1 commit intojruby:masterfrom
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Note that JRuby 10 could use a different patch proposed in #8516 that uses |
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Ok clearly I botched this. Will circle back. |
The call to Math.multiplyExact works very well when the result does not overflow, skipping range checks and using the host CPU's support for overflow checks. However when we are dancing on the range boundary and multiplyExact fails repeatedly, the cost of raising all those exceptions massively outweighs the gains. This is the primary cause of performance issues reported in jruby#8516. This patch reverts to a version of the old range-checking logic. Performance on the bug report's benchmark is an order of magnitude faster for the two cases that seemed to overflow a lot, and the other cases do not seem to degrade. Fixes jruby#8516
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New patch looks clean enough. I'm only doing this one targeted fix since we have alternatives in JRuby 10 using Java 21. |
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The call to Math.multiplyExact works very well when the result does not overflow, skipping range checks and using the host CPU's support for overflow checks. However when we are dancing on the range boundary and multiplyExact fails repeatedly, the cost of raising all those exceptions massively outweighs the gains.
This is the primary cause of performance issues reported in #8516.
This patch reverts to a version of the old range-checking logic. Performance on the bug report's benchmark is an order of magnitude faster for the two cases that seemed to overflow a lot, and the other cases do not seem to degrade.
Fixes #8516