Don't version BNDCHK based on an IV if the loop test is backwards - #7250
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For an increasing loop-driving IV, the loop test must impose an upper bound, e.g. while (i < n), whereas for a decreasing loop-driving IV, the loop test must impose a lower bound instead, e.g. while (i >= n). Otherwise, the predicted maximum iteration count will be wrong, which could allow a bound check to be incorrectly skipped. Loop versioner will now check to ensure that the direction of the loop test agrees with the sign of the step of the loop-driving IV.
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@vijaysun-omr, would you mind reviewing? |
vijaysun-omr
approved these changes
Feb 8, 2024
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jenkins build all |
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jenkins build riscv |
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Failures look to be infra related. The change itself looks conservative/safe to me and in common code. Merging. |
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For an increasing loop-driving IV, the loop test must impose an upper bound, e.g.
while (i < n), whereas for a decreasing loop-driving IV, the loop test must impose a lower bound instead, e.g.while (i >= n). Otherwise, the predicted maximum iteration count will be wrong, which could allow a bound check to be incorrectly skipped.Loop versioner will now check to ensure that the direction of the loop test agrees with the sign of the step of the loop-driving IV.
Fixes eclipse-openj9/openj9#18803