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From: Glen Nakamura <glen@imodulo.com> To: nobody@gcc.gnu.org Cc: gcc-prs@gcc.gnu.org, Subject: Re: optimization/8165: builtin string functions SEGV on alpha-pc-linux-gnu at -O2 Date: Tue, 08 Oct 2002 16:16:00 -0000 [thread overview] Message-ID: <20021008231601.7162.qmail@sources.redhat.com> (raw) The following reply was made to PR optimization/8165; it has been noted by GNATS. From: Glen Nakamura <glen@imodulo.com> To: Richard Henderson <rth@redhat.com>, gcc-gnats@gcc.gnu.org, gcc-bugs@gcc.gnu.org Cc: Subject: Re: optimization/8165: builtin string functions SEGV on alpha-pc-linux-gnu at -O2 Date: Tue, 8 Oct 2002 13:13:26 -1000 On Tue, Oct 08, 2002 at 03:20:53PM -0700, Richard Henderson wrote: > I get the feeling this is simply papering over the problem. > I'll continue to investigate... Thanks, you are quite possibly right. There was a bunch of things happening, and I don't fully understand the semantics of REG_EQUAL notes. I don't have the original rtx dumps, but from memory things looked like this before gcse: SET A ... BEGIN_LOOP ... SET B USE B REG_EQUAL B After gcse USE B is replaced with USE A, but REG_EQUAL still refers to B: SET A ... BEGIN_LOOP ... SET B USE A REG_EQUAL B Then I think the loop pass moved USE A out of the loop (above SET B): SET A ... USE A REG_EQUAL B BEGIN_LOOP ... SET B Eventually, SET B is determined dead and removed but the REG_EQUAL referring to it still exists... Then for some reason, the REG_EQUAL note gets used and bad things happen. One bad side-effect is that life-analysis determines B is live at the entry of basic block 0. I hope this helps. - glen
next reply other threads:[~2002-10-08 23:16 UTC|newest] Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top 2002-10-08 16:16 Glen Nakamura [this message] -- strict thread matches above, loose matches on Subject: below -- 2002-10-14 11:16 Richard Henderson 2002-10-12 11:46 Glen Nakamura 2002-10-11 17:56 Richard Henderson 2002-10-11 16:26 Glen Nakamura 2002-10-11 16:13 rth 2002-10-11 15:46 Richard Henderson 2002-10-08 15:26 Richard Henderson 2002-10-07 18:26 Glen Nakamura 2002-10-07 17:56 glen
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