[ConstraintElim] Extend AND implication logic to support OR as well. (#76044)

Extend the logic check if an operand of an AND is implied by the other
to also support OR. This is done by checking if

[ConstraintElim] Extend AND implication logic to support OR as well. (#76044)

Extend the logic check if an operand of an AND is implied by the other
to also support OR. This is done by checking if !op1 implies op2 or vice
versa.

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[ConstraintElim] Check if second op implies first for And. (#75750)

Generalize checkAndSecondOpImpliedByFirst to also check if the second
operand implies the first.

[ConstraintElim] Remove dead compares after simplification.

Remove compares after replacing all uses. Cleaning dead compares can
enable additional simplifications when adjusting the position of the

[ConstraintElim] Remove dead compares after simplification.

Remove compares after replacing all uses. Cleaning dead compares can
enable additional simplifications when adjusting the position of the
pass slightly. In particular, it seems like the additional dead
instructions may prevent SimplifyCFG performing some folds.

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D158760

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[ConstraintElim] Try to use first cmp to prove second cmp for ANDs.

This patch extends the existing logic to handle cases where we have
branch conditions of the form (AND icmp, icmp) where the first

[ConstraintElim] Try to use first cmp to prove second cmp for ANDs.

This patch extends the existing logic to handle cases where we have
branch conditions of the form (AND icmp, icmp) where the first icmp
implies the second. This can improve results in some cases, e.g. if
SimplifyCFG folded conditions from multiple branches to an AND.

The implementation handles this by adding a new type of check
(AndImpliedCheck), which are queued before conditional facts for the same
block.

When encountering AndImpliedChecks during solving, the first condition
is optimistically added to the constraint system, then we check if the
second icmp can be simplified, and finally the newly added entries are
removed.

The reason for doing things this way is to avoid clashes with signed
<-> unsigned condition transfer, which require us to re-order facts to
increase effectiveness.

Reviewed By: nikic, antoniofrighetto

Differential Revision: https://reviews.llvm.org/D151799

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[ConstraintElim] Add tests for GEPs with signed predicates.