[Bug rtl-optimization/52484] New: Wrong code from ce3 pass (deletes insn)

[gjl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52484

             Bug #: 52484
           Summary: Wrong code from ce3 pass (deletes insn)
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: gjl@gcc.gnu.org
            Target: avr


The following code for AVR target that reads from address space __memx result
in wrong code:

long readx (const __memx long *p)
{
    return *p;
}

== compile ==

$ avr-gcc flash.c -S -dp -Os -mmcu=avr51 -da

== configure ==

../../gcc.gnu.org/trunk/configure --target=avr --prefix=/gnu/install/gcc-4.7
--disable-nls --with-dwarf2 --enable-checking=yes,rtl --enable-languages=c,c++

GNU C (GCC) version 4.8.0 20120304 (experimental) (avr)

SVN 184887 from 2012-03-04

To see the bug RTL dumps will follow.

There is really bloaty code from lower-subreg that splits the 4-byte move into
4 individual byte moves. 

After pass .peephole2 there are 4 xload_qi_libgcc insns that perform these
moves.

After pass .ce3 one of these moves is gone, this is wrong because no byte must
be thrown away.