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Subject: [Bug testsuite/55186] New: gcc.dg/const-uniq-1.c fails due to vector expected but not being in the constant pool
Date: Sat, 03 Nov 2012 04:42:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55186

             Bug #: 55186
           Summary: gcc.dg/const-uniq-1.c fails due to vector expected but
                    not being in the constant pool
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: testsuite
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: hp@gcc.gnu.org
            Target: cris-axis-elf


Created attachment 28601
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=28601
const-uniq-1.c.004t.gimple

While technically this is a regression, the reason for the brief PASS period is
likely related to a temporary severe bug in the source tree rather than the
more common sequence: a conscious change foiled by a later bug. This is a rare
event!

This test previously failed, started passing somewhere in the (]-range
193059:193061 (likely due to the bug in r193061) and started failing again
somewhere in the (]-range 193063:193070 (likely due to the bugfix in r193064).
At r193109, the const-uniq-1.c.004t.gimple dump is as attached: no label
present for the expected constant-pool entry.

The assembly output for the vector initializations are piecewise, one for each
element:
        moveq 1,$r9
        move.d $r9,[$sp+4]
The test assumes a single vector in the constant pool supposedly used with some
memcpy-equivalent (call or in-line expansion).  At first glance, the piecewise
initialization might seem suboptimal, but a memcpy call would *not* be better
for -Os for this target, when counting the constant vector (well, twice). 
Piecewise initialization would be optimal - if the storing instructions use
post-increment instead of indexing, as expected by the specified relevant
target macros.  (N.B.: poor autoincdec generation is a long-standing flaw in
gcc covered by PRs elsewhere).
Constant-pool vectors and memcpy are optimal for e.g. vectors four times as
large; will propose such a patch for this test-case.