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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/108129] nop_atomic_bit_test_and_p is too
 bloated
Date: Thu, 15 Dec 2022 17:57:35 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108129

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Alexander Monakov from comment #0)
> match.pd has multi-pattern matcher 'nop_atomic_bit_test_and_p'.
>=20
> It expands to ~38 KLOC in gimple-match.cc and ~350 KB in the compiled bin=
ary.
>=20
> There has to be a better way than repeatedly emitting the match pattern f=
or
> each member of {ATOMIC,SYNC}_FETCH_{AND,OR_XOR}_N :)

It's the way the matcher works - if you can think of a better way of
code-generating it within the constraints:
 - earlier patterns in match.pd should match first in case there are multip=
le
matches
 - matching time should ideally be O(size of the pattern) rather than O(siz=
e of
match.pd)

The 2nd constraint isn't currently fulfilled because of the first constraint
(or how that is implemented).  The 2nd constraint was the original design
goal to make frequent "re-folding" cheap.  The first constraint was impleme=
nted
to allow pattern ordering to disambiguate "overlapping" matches.

Writing a different code generation in genmatch should be possible, the
(lowered) AST is available.=