Re: Fix 'gcc.dg/tree-ssa/return-value-range-1.c' for 'char' defaulting to 'unsigned' (was: Propagate value ranges of return values)

[Thomas Schwinge <thomas@codesourcery.com>]

Hi!

On 2023-11-22T11:51:02+0100, Christophe Lyon <christophe.lyon@linaro.org> wrote:
> On Tue, 21 Nov 2023 at 22:24, Thomas Schwinge <thomas@codesourcery.com> wrote:
>> On 2023-11-19T16:05:42+0100, Jan Hubicka <hubicka@ucw.cz> wrote:
>> > --- /dev/null
>> > +++ b/gcc/testsuite/gcc.dg/tree-ssa/return-value-range-1.c
>>
>> Pushed to master branch commit a0240662b22312ffb3e3fefb85f258ab0e7010f4
>> "Fix 'gcc.dg/tree-ssa/return-value-range-1.c' for 'char' defaulting to
>> 'unsigned'", see attached.  On powerpc64le-linux-gnu ('char' defaulting
>> to 'unsigned') I still saw:
>>
>>     /tmp/ccd1xwD7.o: In function `test':
>>     return-value-range-1.c:(.text+0x50): undefined reference to `link_error'
>>
> We do see the same error in our CI (Thomas, normally you have received
> a notification because your patch turned ERROR in FAIL)

Yes, I have; and I even tried to log in there, to point to my commit
mentioned above, which is meant to address this issue -- please let me
know if you're still seeing the FAIL after that commit.

> Thomas, you said in another email that adding -O2 avoids the linker
> error with missing link_error(), but I don't see how that would be
> possible?

That's the gist of Honza's "Propagate value ranges of return values"
optimization, per my understanding: from 'int a(signed char c)' doing
'return c;' figure out that 'a(d) > 200)' is always false (due to
'-128 <= c <= 127)'.

> (and hence I expect the error you quoted above to happen)
>
> So should we use dg-compile instead of dg-link? Not sure what the
> original intention was?

No, the idea really is to prove that the 'link_error ()' call is
unreachable.


Grüße
 Thomas


>> > @@ -0,0 +1,22 @@
>> > +/* { dg-do ling } */
>> > +/* { dg-options "-O1 -dump-tree-evrp-details" } */
>> > +__attribute__ ((__noinline__))
>> > +int a(char c)
>> > +{
>> > +     return c;
>> > +}
>> > +void link_error ();
>> > +
>> > +void
>> > +test(int d)
>> > +{
>> > +     if (a(d) > 200)
>> > +             link_error ();
>> > +}
>> > +int
>> > +main(int argc, char **argv)
>> > +{
>> > +     test(argc);
>> > +     return 0;
>> > +}
>> > +/* { dg-final { scan-tree-dump-times "Recording return range" 2 "evrp"} } */
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