[Bug rtl-optimization/51374] [avr] insn combine reorders volatile memory accesses

[gjl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51374

Georg-Johann Lay <gjl at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
      Known to work|                            |4.7.0
           Keywords|                            |wrong-code
   Last reconfirmed|                            |2011-12-01
          Component|c                           |rtl-optimization
                 CC|                            |gjl at gcc dot gnu.org
               Host|i386-redhat-linux           |
     Ever Confirmed|0                           |1
            Summary|Volatile access reordered.  |[avr] insn combine reorders
                   |                            |volatile memory accesses
   Target Milestone|---                         |4.6.3
      Known to fail|                            |4.6.2

--- Comment #1 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2011-12-01 09:57:16 UTC ---
Please, supply informations that are needed to reproduce bugs like explained in
http://gcc.gnu.org/bugs.html/#need when you report bugs like compiler switches
applied. Thanks.

To reprodoce, optimization must be turned on:

$ avr-gcc-4.6.2 test.c -Os -dp -S

__vector_18:
    in r24,44-0x20     ;  8    *movqi/4    [length = 1]
    sbis 43-0x20,4     ;  12    *sbix_branch    [length = 2]
    rjmp .L1
    lds r24,slot.1198     ;  14    *movhi/2    [length = 4]
    lds r25,slot.1198+1
    ldi r18,hi8(-2)     ;  15    *cmphi/5    [length = 3]
    cpi r24,lo8(-2)
    cpc r25,r18
    brne .L1     ;  16    branch    [length = 1]
    ldi r24,lo8(-1)     ;  18    *movhi/4    [length = 2]
    ldi r25,hi8(-1)
    sts slot.1198+1,r25     ;  19    *movhi/3    [length = 4]
    sts slot.1198,r24
.L1:
    ret     ;  29    return    [length = 1]


avr-gcc-4.7.0 (trunk 181838) compiles correct with -O1/2/s/3, here with -Os:

__vector_18:
    in r24,0xb     ;  6    movqi_insn/4    [length = 1]
    in r25,0xc     ;  8    movqi_insn/4    [length = 1]
    sbrs r24,4     ;  11    *sbrx_branchqi    [length = 2]
    rjmp .L1
    lds r24,slot.1321     ;  13    *movhi/3    [length = 4]
    lds r25,slot.1321+1
    adiw r24,2     ;  14    *cmphi/7    [length = 1]
    brne .L1     ;  15    branch    [length = 1]
    ldi r24,lo8(-1)     ;  17    *movhi/5    [length = 2]
    ldi r25,lo8(-1)
    sts slot.1321+1,r25     ;  18    *movhi/4    [length = 4]
    sts slot.1321,r24
.L1:
    ret     ;  35    return    [length = 1]