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Date: Wed, 11 Mar 2009 07:25:00 -0000
Subject: [Bug c++/39429]  New: compiler create bad asm codes.
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From: "ryos at sinby dot com" <gcc-bugzilla@gcc.gnu.org>
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the Compiler creates bad asm codes from following source.

bool
ArmGccTest::useOffScreen()
{
    if ((mapsize - size) < 16*1024)
        return false;

    return true;
}


        .text
        .align  2
        .global _ZN10ArmGccTest12useOffScreenEv
        .type   _ZN10ArmGccTest12useOffScreenEv, %function
_ZN10ArmGccTest12useOffScreenEv:
        .fnstart
.LFB2:
        @ Function supports interworking.
        @ args = 0, pretend = 0, frame = 0
        @ frame_needed = 0, uses_anonymous_args = 0
        @ link register save eliminated.
        ldr     r0, [r0, #1080]
        ldr     r3, [r0, #1084]
        sub     r0, r0, r3
        cmp     r0, #16384
        movcc   r0, #0
        movcs   r0, #1
        bx      lr

r0 is assigned for "this". however r0 is rewritten to use "mapsize", so r3 is
broken.  You can see this problem by following simple c++ source.

class ArmGccTest {
private:
        unsigned int value001;
....
....
....

        unsigned int value109;
        unsigned int value10a;
        unsigned int value10b;
        unsigned int value10c;
        unsigned int value10d;

        unsigned int mapsize;
        unsigned int size;

        unsigned int value10e;

        bool useOffScreen();
};


-- 
           Summary: compiler create bad asm codes.
           Product: gcc
           Version: 4.3.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: ryos at sinby dot com
  GCC host triplet: arm-linux, i386-linux, i386-freebsd
GCC target triplet: arm-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39429