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From: "chenglulu at loongson dot cn" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/108357] [13 Regression] Dead Code Elimination
 Regression at -O2 since r13-4607-g2dc5d6b1e7ec88
Date: Thu, 13 Apr 2023 12:16:06 +0000
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X-Bugzilla-Component: tree-optimization
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X-Bugzilla-Keywords: missed-optimization
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108357

--- Comment #12 from chenglulu <chenglulu at loongson dot cn> ---
(In reply to Xi Ruoyao from comment #11)
> (In reply to chenglulu from comment #10)
> > (In reply to Xi Ruoyao from comment #5)
> > > The test fails on loongarch64-linux-gnu.  foo is kept in 114t.threadf=
ull1,
> > > but removed in 135t.forwprop3.
> > >=20
> > > Does this mean something is wrong for LoongArch, or we should simply =
check
> > > the tree dump in a later pass (for e.g. 254t.optimized)?
> >=20
> > If the definition of the macro DEFAULT_SIGNED_CHAR is changed to 0, the=
 test
> > case can pass the test. I guess it is because the definition of
> > DEFAULT_SIGNED_CHAR affects the optimization of the ccp pass, resulting=
 in
> > some blocks that cannot be removed, resulting in the failure of this te=
st
> > case.
>=20
> Hmm, but we cannot change DEFAULT_SIGNED_CHAR or we'll break ABI and API
> everywhere.  And x86_64-linux-gnu also uses DEFAULT_SIGNED_CHAR=3D1.

Uh, I didn't notice this, I'll keep looking.=