[Bug c/29592] Unending loops

[darkjames at darkjames dot ath dot cx]

--- Comment #1 from darkjames at darkjames dot ath dot cx  2006-10-25 16:12 
---
Created an attachment (id=12490)
 -- (http://gcc.gnu.org/bugzilla/attachment.cgi?id=12490action=view)
First testcase

First testcase loops unending with -O2, not loops with -O2 -fno-strict-aliasing
|| 
-fstrict-aliasing -O1


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29592

[Bug c/29592] Unending loops

[darkjames at darkjames dot ath dot cx]

--- Comment #2 from darkjames at darkjames dot ath dot cx  2006-10-25 16:13 
---
Created an attachment (id=12491)
 -- (http://gcc.gnu.org/bugzilla/attachment.cgi?id=12491action=view)
Second testcase

test1.c + added printf() to loop, not loops with -O2 


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29592

[Bug c/29592] Unending loops

[darkjames at darkjames dot ath dot cx]

--- Comment #3 from darkjames at darkjames dot ath dot cx  2006-10-25 16:20 
---
By the way, it's possible to fix the code in other way than using unions?
It just need to work both for wchar_t strings and normal strings...
If you have some ideas how, it'll be nice if you give me some hint...
maybe use char * everywhere and use:

real_char_index = index * (config_use_unicode * sizeof(wchar_t)) ? 


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29592

[Bug c/29592] Unending loops

[pinskia at gcc dot gnu dot org]

--- Comment #4 from pinskia at gcc dot gnu dot org  2006-10-25 16:45 ---
In the both case, you are accessing wchar * via char * which causes an
alias violation.


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pinskia at gcc dot gnu dot org changed:

   What|Removed |Added

 Status|UNCONFIRMED |RESOLVED
 Resolution||INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29592

[Bug c/29592] Unending loops

[darkjames at darkjames dot ath dot cx]

--- Comment #5 from darkjames at darkjames dot ath dot cx  2006-10-25 17:11 
---
Yeah, I know, but why gcc generate good code if we add that printf to test1.c
(test2.c) ? It's still wchar * - char * still aliasing violation.

or if we replace:
__SN(str, 1); with
str = (CHAR_T *) (((char *) str) + 1);

it generate good code too. it's still aliasing violation?


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29592

[Bug c/29592] Unending loops

[pinskia at gcc dot gnu dot org]

--- Comment #6 from pinskia at gcc dot gnu dot org  2006-10-25 17:18 ---
(In reply to comment #5)
 Yeah, I know, but why gcc generate good code if we add that printf to test1.c
 (test2.c) ? It's still wchar * - char * still aliasing violation.

Yes but there is a barrier which cause optimizations not to happen.
 
 or if we replace:
 __SN(str, 1); with
 str = (CHAR_T *) (((char *) str) + 1);
 
 it generate good code too. it's still aliasing violation?

No, that is legal as you are not accessing str (wchar_t*) as a char* any
longer but as a wchar_t*.  You access str as a wchar_t* and then cast that
value to a char* and then add one and then cast back to wchar_t* which
causes the above code to be valid and defined.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29592

[Bug c/29592] Unending loops

[darkjames at darkjames dot ath dot cx]

--- Comment #7 from darkjames at darkjames dot ath dot cx  2006-10-25 17:24 
---
Ok, one more question, is it possible to gcc print some warnings about code
like that? Cause even with -Wall it doesn't ;( 
gcc4 is quite more verbose than gcc3 so I think 
It'll be better to print warning about situation which doesn't even generate
invalid code...

which actually -Wstrict-aliasing does (according to manpage), but neither
-Wstrict-aliasing nor -Wstrict-aliasing=2 prints warning in that testcode...

I hope it's possible, thx for all.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29592