[Bug gas/803] New: gas should avoid F-unit NOPs (and B-unit probably, too)

[davidm at hpl dot hp dot com]

Chips derived from McKinley-core (Itanium 2, etc.) have an anomaly which can
cause stalls if an F-unit instruction (including a NOP) is issued right after
reading certain application registers (such as ar.bsp).  Furthermore,
power-considerations also argue against the use of F-unit instructions unless
they're really needed.

Similarly, using B-unit NOPs is probably not a great idea for McKinley-derived
cores: certain templates with B unit instructions cause split-issue and the BBB
template in particular causes a branch-prediction anomaly (the first two
branches are predicated based on the slot 0 hints.

I'll attach a patch which appears to fix this problem.  If it looks OK, please
check it in.

Note: the new policy won't be optimal for Itanium (Merced) chips.  I don't think
anyone will care.

-- 
           Summary: gas should avoid F-unit NOPs (and B-unit probably, too)
           Product: binutils
           Version: 2.17 (HEAD)
            Status: NEW
          Severity: normal
          Priority: P2
         Component: gas
        AssignedTo: unassigned at sources dot redhat dot com
        ReportedBy: davidm at hpl dot hp dot com
                CC: bug-binutils at gnu dot org,hjl at lucon dot org
 GCC build triplet: ia64-linux
  GCC host triplet: ia64-linux
GCC target triplet: ia64-linux


http://sources.redhat.com/bugzilla/show_bug.cgi?id=803

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