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Re: [PATCH] -Wtautological-compare: fix comparison of macro expansions


On Wed, 2018-12-19 at 22:01 -0500, David Malcolm wrote:
> On Wed, 2018-12-19 at 17:27 -0600, Aaron Sawdey wrote:
> > Assuming you applied this as svn 267273, it causes bootstrap
> > failure
> > on powerpc64le-unknown-linux-gnu. Stage 2 fails with multiple
> > instances
> > of this error:
> > 
> > ../../trunk-base/gcc/c-family/c-pragma.c: In function ‘void
> > handle_pragma_scalar_storage_order(cpp_reader*)’:
> > ../../trunk-base/gcc/c-family/c-pragma.c:417:24: error: self-
> > comparison always evaluates to false [-Werror=tautological-compare]
> >   417 |   if (BYTES_BIG_ENDIAN != WORDS_BIG_ENDIAN)
> >       |                        ^~
> > ../../trunk-base/gcc/c-family/c-attribs.c: In function ‘tree_node*
> > handle_scalar_storage_order_attribute(tree_node**, tree, tree, int,
> > bool*)’:
> > ../../trunk-base/gcc/c-family/c-attribs.c:1401:24: error: self-
> > comparison always evaluates to false [-Werror=tautological-compare]
> >  1401 |   if (BYTES_BIG_ENDIAN != WORDS_BIG_ENDIAN)
> >       |                        ^~
> > ../../trunk-base/gcc/builtins.c: In function ‘rtx_def*
> > c_readstr(const char*, scalar_int_mode)’:
> > ../../trunk-base/gcc/builtins.c:830:28: error: self-comparison
> > always
> > evaluates to false [-Werror=tautological-compare]
> >   830 |       if (BYTES_BIG_ENDIAN != WORDS_BIG_ENDIAN
> >       |                            ^~
> > ../../trunk-base/gcc/combine.c: In function ‘int
> > rtx_equal_for_field_assignment_p(rtx, rtx, bool)’:
> > ../../trunk-base/gcc/combine.c:9668:28: error: self-comparison
> > always
> > evaluates to false [-Werror=tautological-compare]
> >  9668 |       if (BYTES_BIG_ENDIAN != WORDS_BIG_ENDIAN)
> >       |                            ^~
> > 
> > Aaron
> 
> Sorry about that.
> 
> Does the following patch help?  (testing in progress here)
[...snip...]

According to comments within PR c++/87504, the patch fixes the
bootstrap on aarch64, and fixes a similar issue on Solaris/SPARC.

It also passed bootstrap&regrtesting on x86_64-pc-linux-gnu.

Given that, I've committed it to trunk as r267299.

Aaron, does this fix the issue you saw?

Thanks, and sorry again about the breakage.
Dave


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