JIT: Improve strength reduction's prediction of loop reversal #104800
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These primary IVs are not going to be removed by the downwards loop transformation, so if we do this we introduce additional primary IVs which (for now) it is the goal not to.
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/azp run runtime-coreclr jitstress, runtime-coreclr libraries-jitstress |
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Stress failures are #104449 and #102706. cc @dotnet/jit-contrib PTAL @AndyAyersMS Diffs with strength reduction enabled (mainly improvements because we strength reduce less...) |
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The current goal is to make sure strength reduction does not introduce new primary IVs. To do so we rely on the downwards-loop transformation to get rid of uses of the primary IV in the loop test.
This PR refines the checks that strength reduction was using to predict whether a use of the primary IV in a loop test will be removed. It should now be the exact same checks as the downwards-transformation uses.
Additionally, it means we can remove
CursorInfo::IsInsideExitTest; we now just avoid creating the cursor in the first place if we know the use will be removable.