[Bug target/11831] [ARM] Logical expression evaluation with condition fields

[Bug target/11831] [ARM] Logical expression evaluation with condition fields

[ramana dot r at gmail dot com]

------- Comment #4 from ramana dot r at gmail dot com  2009-03-13 12:33 -------
With Mainline today it looks worse -    

     stmfd   sp!, {r4, lr}
        mov     r4, r0
        bl      func
        add     r0, r4, r0
        ldrb    r3, [r0, #-4]   @ zero_extendqisi2
        cmp     r3, #97
        beq     .L6
.L2:
        mov     r0, #0
        ldmfd   sp!, {r4, pc}
.L6:
        ldrb    r3, [r0, #-3]   @ zero_extendqisi2
        cmp     r3, #98
        bne     .L2
        ldrb    r3, [r0, #-2]   @ zero_extendqisi2
        cmp     r3, #99
        bne     .L2
        ldrb    r0, [r0, #-1]   @ zero_extendqisi2
        cmp     r0, #100
        movne   r0, #0
        moveq   r0, #1
        ldmfd   sp!, {r4, pc}


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ramana dot r at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rearnsha at arm dot com,
                   |                            |ramana dot r at gmail dot
                   |                            |com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11831

[Bug middle-end/11831] [ARM] Logical expression evaluation with condition fields

[rearnsha at gcc dot gnu dot org]

------- Comment #5 from rearnsha at gcc dot gnu dot org  2009-03-17 11:41 -------
This isn't something that should be fixed in the back-end, but most likely an
enhancement to a pass such as ifcvt.  To handle this case we would have to
teach ifcvt about dominated conditions and conditional comparisons -- at
present it can only handle conditional insns that do not modify the predicating
condition.


-- 

rearnsha at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|target                      |middle-end
           Priority|P3                          |P4


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11831

[Bug middle-end/11831] [ARM] Logical expression evaluation with condition fields

[steven at gcc dot gnu dot org]

------- Comment #6 from steven at gcc dot gnu dot org  2010-02-08 11:18 -------
Does the ARM backend already support conditional compares?


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11831

[Bug middle-end/11831] [ARM] Logical expression evaluation with condition fields

[rearnsha at gcc dot gnu dot org]

------- Comment #7 from rearnsha at gcc dot gnu dot org  2010-02-08 11:26 -------
(In reply to comment #6)
> Does the ARM backend already support conditional compares?
> 

Yes, but only by manipulating store-flag sequences in the combine pass.  That's
a poor-man's implementation and it can lead to some sequences that don't get
fully simplified.

That code could be compiled to 

        ldrb    r3, [r4, #-4]   @ zero_extendqisi2
        cmp     r3, #97
        ldrbeq  r3, [r4, #-3]   @ zero_extendqisi2
        cmpeq   r3, #98
        ldrbeq  r3, [r4, #-2]   @ zero_extendqisi2
        cmpeq   r3, #99
        ldrbeq  r3, [r4, #-1]   @ zero_extendqisi2
        cmpeq   r3, #100

but the compiler currently has no chance of achieving that.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11831