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Date: Thu, 02 Jul 2009 07:39:00 -0000
Subject: [Bug target/40615]  New: unnecessary CSE
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From: "carrot at google dot com" <gcc-bugzilla@gcc.gnu.org>
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Compile the attached source code with options -march=armv5te -mthumb -Os
-fno-exceptions, gcc generates:

        push    {r4, lr}
        sub     sp, sp, #8
        add     r4, sp, #4    // redundant
        mov     r0, r4        // add  r0, sp, 4
        bl      _ZN1XC1Ev
        mov     r0, r4        // add  r0, sp, 4
        bl      _Z3barP1X
        mov     r0, r4        // add  r0, sp, 4
        bl      _ZN1XD1Ev
        add     sp, sp, #8
        @ sp needed for prologue
        pop     {r4, pc}

As mentioned in the comments, the cse is redundant. We can recompute the value
of (sp + 4) each time we want it. With this method we can save one instruction.


-- 
           Summary: unnecessary CSE
           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=40615