[MachinePipeliner] Add PipelinerLoopInfo hooks to reuse the reg-pressure detector#3431
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…ure detector The generic MachinePipeliner register-pressure detector (added in llvm#74807) was only reachable via the global -pipeliner-register-pressure flag, which cannot be enabled per-target, and it judges pressure against generic per-pressure-set limits. Add two PipelinerLoopInfo hooks so a target can reuse that detector on its own terms: - shouldLimitRegPressure(): opt the loop into the detector without the global flag. The detector runs inside the II search, so a schedule rejected on register pressure is retried at a higher II rather than abandoning the loop. - isScheduleRegPressureTooHigh(MaxSetPressure): let the target replace the detector's generic per-pressure-set limit check with its own verdict, or return nullopt to keep that check. Both hooks default to preserving current behavior, so targets that do not override them are unaffected: the detector stays gated on -pipeliner-register-pressure and the generic per-set check is unchanged. Exercised by the AMDGPU adoption in the following commit.
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The generic MachinePipeliner register-pressure detector (added in llvm#74807)
was only reachable via the global -pipeliner-register-pressure flag, which
cannot be enabled per-target, and it judges pressure against generic
per-pressure-set limits. Add two PipelinerLoopInfo hooks so a target can
reuse that detector on its own terms:
global flag. The detector runs inside the II search, so a schedule
rejected on register pressure is retried at a higher II rather than
abandoning the loop.
detector's generic per-pressure-set limit check with its own verdict, or
return nullopt to keep that check.
Both hooks default to preserving current behavior, so targets that do not
override them are unaffected: the detector stays gated on
-pipeliner-register-pressure and the generic per-set check is unchanged.
Exercised by the AMDGPU adoption in the following commit.