[Bug tree-optimization/108357] [13 Regression] Dead Code Elimination Regression at -O2 since r13-4607-g2dc5d6b1e7ec88

[xry111 at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108357

--- Comment #11 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
(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.threadfull1,
> > but removed in 135t.forwprop3.
> > 
> > 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)?
> 
> 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 test
> case.

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=1.