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From: "glisse at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug rtl-optimization/55549] New: zero_extend and vectors
Date: Fri, 30 Nov 2012 14:29:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55549

             Bug #: 55549
           Summary: zero_extend and vectors
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: glisse@gcc.gnu.org


Hello,

the documentation of zero_extend says:

@findex zero_extend
@item (zero_extend:@var{m} @var{x})
Represents the result of zero-extending the value @var{x}
to machine mode @var{m}.  @var{m} must be a fixed-point mode
and @var{x} a fixed-point value of a mode narrower than @var{m}.

However, try_combine will happily call:

                SUBST (*split, gen_rtx_ZERO_EXTEND (split_mode,
                                                    SUBREG_REG (*split)));

without many checks. In particular, in PR54855, it tries:

     (zero_extend:V2DF (mem/u/c:DF ...))

It isn't a bug because nothing will recognize this pattern and it will be
rejected, but it seems it would be good to add a few conditions.