[Bug lto/42088] flag_gtoggle in free_lang_data hides -fcompare-debug errors

["rguenther at suse dot de" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #4 from rguenther at suse dot de  2009-11-18 16:51 -------
Subject: Re:  flag_gtoggle in free_lang_data hides -fcompare-debug
 errors

On Wed, 18 Nov 2009, aoliva at gcc dot gnu dot org wrote:

> ------- Comment #3 from aoliva at gcc dot gnu dot org  2009-11-18 16:30 -------
> Different UIDs affect hash table walks, which in turn may affect codegen. 
> We've had several -g/-g0 codegen differences ultimately caused by decl UID
> differences, and they were detected and fixed long before -fcompare-debug was
> even introduced, i.e., they were detected with the compare-debug script that
> compares actual generated code.
> 
> That's why -fcompare-debug must report such differences.  Even if the code ends
> up the same in one particular testcase, supersets of that testcase would likely
> diverge.  Disregarding the UIDs in -fcompare-debug would hide errors.

Sorry, but hashtable walks are always broken if codegen depends on them
and you do not ensure proper ordering.  Enforcing same UIDs for -g/-g0
just forces us to use more memory than necessary.

Richard.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42088