From: kenner@vlsi1.ultra.nyu.edu (Richard Kenner)
To: gcc@gcc.gnu.org
Subject: Question on cfg_remove_useless_stmts_bb
Date: Fri, 13 Aug 2004 19:59:00 -0000 [thread overview]
Message-ID: <10408131953.AA16722@vlsi1.ultra.nyu.edu> (raw)
I'm getting a failure on c-torture/execute/930513-2.c with -O3 and what's
happening is that the out of ssa pass is looking at
if (j != i) goto <L1>; else goto <L2>;
...
<L2>:;
i = i + 1;
j = i;
The cfg_remove_useless_stmts_bb knows that J and I are equal. So when it
gets to the "j = i" assignment, it deletes it. The problem is that it
doesn't notice that "i = i + 1" clobbers the equality relation.
I don't think it's sufficient to test for an assignment to VAL here because
I think VAL can be an expression since we are no longer in GIMPLE, but
I'm not sure.
Hence my question.
I don't know why this test isn't failing for everybody, so I suspect this
is some sort of latent bug somehow. (Or else I'm missing something,
which is quite possible.)
next reply other threads:[~2004-08-13 19:50 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-08-13 19:59 Richard Kenner [this message]
2004-08-13 20:19 ` Diego Novillo
2004-08-17 8:26 ` Jeffrey A Law
2004-08-13 21:29 Richard Kenner
2004-08-17 12:31 Richard Kenner
2004-08-17 15:49 ` Jeffrey A Law
2004-08-17 16:49 Richard Kenner
2004-08-18 8:42 ` Jeffrey A Law
2004-08-18 11:51 Richard Kenner
2004-08-18 11:52 Richard Kenner
2004-09-01 6:22 ` Jeffrey A Law
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