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* [Bug target/42496]  New: wrong if conversion optimization
@ 2009-12-25  8:13 carrot at google dot com
  2009-12-25  8:14 ` [Bug target/42496] " carrot at google dot com
  2009-12-27  0:46 ` steven at gcc dot gnu dot org
  0 siblings, 2 replies; 3+ messages in thread
From: carrot at google dot com @ 2009-12-25  8:13 UTC (permalink / raw)
  To: gcc-bugs

Compile the attached test case with options -Os, I can get the ideal result:

foo:
        cmp     r0, #0
        ldr     r3, .L5
        movne   r2, #10
        moveq   r2, #20
        str     r2, [r3, #0]
        bx      lr

But when I changed the options to -O2, I got:

foo:
        cmp     r0, #0
        ldrne   r3, .L4            // A
        ldreq   r3, .L4            // B
        movne   r2, #10
        moveq   r2, #20
        strne   r2, [r3, #0]       // C
        streq   r2, [r3, #0]       // D
        bx      lr

Instructions A/B/C/D should not executed conditionally since they do the same
thing in either case.

Similarly when I changed to options to -Os -fpic, I got:

foo:
        ldr     r3, .L5
        ldr     r2, .L5+4
.LPIC0:
        add     r3, pc, r3
        cmp     r0, #0
        ldrne   r3, [r3, r2]     // E
        ldreq   r3, [r3, r2]     // F
        movne   r2, #10
        moveq   r2, #20
        str     r2, [r3, #0]
        bx      lr

Instructions E/F should not execute conditionally.


-- 
           Summary: wrong if conversion optimization
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: carrot at google dot com
 GCC build triplet: i686-linux
  GCC host triplet: i686-linux
GCC target triplet: arm-eabi


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42496


^ permalink raw reply	[flat|nested] 3+ messages in thread
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-- links below jump to the message on this page --
2009-12-25  8:13 [Bug target/42496] New: wrong if conversion optimization carrot at google dot com
2009-12-25  8:14 ` [Bug target/42496] " carrot at google dot com
2009-12-27  0:46 ` steven at gcc dot gnu dot org

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