[InstCombine] Simplify and/or of icmp eq with op replacement (#70335)

and/or in logical (select) form benefit from generic simplifications via
simplifyWithOpReplaced(). However, the corresponding fold for plain
and/or currently does not exist.

Similar to selects, there are two general cases for this fold
(illustrated with `and`, but there are `or` conjugates).

The basic case is something like `(a == b) & c`, where the replacement
of a with b or b with a inside c allows it to fold to true or false.
Then the whole operation will fold to either false or `a == b`.

The second case is something like `(a != b) & c`, where the replacement
inside c allows it to fold to false. In that case, the operand can be
replaced with c, because in the case where a == b (and thus the icmp is
false), c itself will already be false.

As the test diffs show, this catches quite a lot of patterns in existing
test coverage. This also obsoletes quite a few existing special-case
and/or of icmp folds we have (e.g. simplifyAndOrOfICmpsWithLimitConst),
but I haven't removed anything as part of this patch in the interest of
risk mitigation.

Fixes #69050.
Fixes #69091.

0 files changed, 0 insertions, 0 deletions