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[Bug gas/5704] Invalid warning about predicate WAW for Itanium


From: wilson at tuliptree dot org
Subject: [Bug gas/5704] Invalid warning about predicate WAW for Itanium
Date: 4 Mar 2008 02:04:50 -0000

------- Additional Comments From wilson at tuliptree dot org  2008-03-04 02:04 
-------
The dependency violation checking code in gas in known to have a number of
problems which are not easy to fix.  This is one of them.

When we see
        .pred.rel.mutex p7, p6
        (p7) cmp.eq p7, p9 = 0, r32
        (p6) cmp.eq p6, p9 = 0, r32
gas assumes that the store to p7 clobbers the mutex between p6 and p7.  However,
since we are testing p7 before it is stored to, and testing p6 before it is
stored to, the mutex does apply, and there should be no DV warning here.

Fixing this requires changing the internal representation of mutexes to include
info about when they were created.  We must also keep info about when each
predicate register is modified.  These changes in turn require other cascading
changes.  This makes it a rather involved fix, and it isn't clear when, or if
ever, it will be fixed.

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         AssignedTo|wilson at specifixinc dot   |wilson at tuliptree dot org
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http://sourceware.org/bugzilla/show_bug.cgi?id=5704

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