[Bug target/50970] Function pointer dereferenced twice in if statement on Arm cpu

[mikpe at it dot uu.se]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50970

--- Comment #7 from Mikael Pettersson <mikpe at it dot uu.se> 2011-11-19 17:42:53 UTC ---
Created attachment 25859
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=25859
reduced test case

Reduced test case.  Running this on i686 shows a single call to func3

>/mnt/scratch/install47/bin/g++ -O2 -Wall pr50970.cc ; ./a.out
TestClass::func3 from 0x8048553

but on ARM we see two calls from different locations:

>/mnt/scratch/install47/bin/g++ -march=armv5te -mtune=arm10tdmi -O2 -Wall pr50970.cc ; ./a.out
TestClass::func3 from 0x8554
TestClass::func3 from 0x8590

Looking at the code for testFunction

void TestClass::testFunction()
{
  if ((this->*_myFunc3)() == 0)
    ;
}

we see not one but two indirect method calls (the blx insns):

_ZN9TestClass12testFunctionEv:
        .fnstart
.LFB16:
        @ args = 0, pretend = 0, frame = 16
        @ frame_needed = 0, uses_anonymous_args = 0
        stmfd   sp!, {r4, lr}
        .save {r4, lr}
        ldr     r1, [r0, #4]
        .pad #16
        sub     sp, sp, #16
        tst     r1, #1
        ldrne   r2, [r0, r1, asr #1]
        ldrne   r3, [r0, #0]
        ldreq   r3, [r0, #0]
        addeq   r1, r0, r1, asr #1
        addne   r1, r0, r1, asr #1
        ldrne   r3, [r2, r3]
        mov     r4, r0
        mov     r0, sp
        blx     r3
        ldr     r3, [sp, #0]
        cmp     r3, #0
        beq     .L14
.L7:
        add     sp, sp, #16
        ldmfd   sp!, {r4, pc}
.L14:
        ldr     r1, [r4, #4]
        add     r0, sp, #8
        tst     r1, #1
        ldrne   r2, [r4, r1, asr #1]
        ldrne   r3, [r4, #0]
        ldreq   r3, [r4, #0]
        addeq   r1, r4, r1, asr #1
        addne   r1, r4, r1, asr #1
        ldrne   r3, [r2, r3]
        blx     r3
        b       .L7