Re: Same cross-gcc toolchain on different hosts produces different target code?

[David Daney <ddaney at caviumnetworks dot com>]

On 03/17/2011 11:20 AM, McCall, Ronald SIK wrote:
> > If you let us in on what exactly the secret differences were, it would
> > be easier to opine on this topic.
>
> Sure thing!  Here is an instruction sequence from the original Solaris toolchain:

Resending to gcc@.  I didn't really want a private message about it.

> fe000230:   54 6a 87 be     rlwinm  r10,r3,16,30,31
> fe000234:   65 49 ff ff     oris    r9,r10,65535
> fe000238:   61 28 ff fc     ori r8,r9,65532
> fe00023c:   6d 07 80 00     xoris   r7,r8,32768
> fe000240:   3c 00 43 30     lis r0,17200
> fe000244:   90 e1 00 0c     stw r7,12(r1)
> fe000248:   90 01 00 08     stw r0,8(r1)
> fe00024c:   3c 80 fe 14     lis r4,-492
> fe000250:   c8 01 00 08     lfd f0,8(r1)
> fe000254:   39 24 82 38     addi    r9,r4,-32200<<<  Instruction sequence #1
> fe000258:   c8 89 00 00     lfd f4,0(r9)<<<  (continued)
> fe00025c:   74 60 00 08     andis.  r0,r3,8
> fe000260:   3c c0 00 01     lis r6,1
> fe000264:   fc 60 20 28     fsub    f3,f0,f4<<<  Instruction sequence #2
> fe000268:   fc 40 18 18     frsp    f2,f3
> fe00026c:   fc 20 10 90     fmr f1,f2
> fe000270:   fc 00 08 1e     fctiwz  f0,f1
> fe000274:   d8 01 00 10     stfd    f0,16(r1)
> fe000278:   80 81 00 14     lwz r4,20(r1)
> fe00027c:   98 86 8f 0d     stb r4,-28915(r6)
> fe000280:   41 82 00 cc     beq-    fe00034c
>
> Here is the same instruction sequence from the newly built Linux toolchain:
>
> fe000230:   54 6a 87 be     rlwinm  r10,r3,16,30,31
> fe000234:   65 49 ff ff     oris    r9,r10,65535
> fe000238:   61 28 ff fc     ori r8,r9,65532
> fe00023c:   6d 07 80 00     xoris   r7,r8,32768
> fe000240:   3c 00 43 30     lis r0,17200
> fe000244:   90 e1 00 0c     stw r7,12(r1)
> fe000248:   90 01 00 08     stw r0,8(r1)
> fe00024c:   3c 80 fe 14     lis r4,-492
> fe000250:   c8 01 00 08     lfd f0,8(r1)
> fe000254:   c9 a4 87 b0     lfd f13,-30800(r4)<<<  Instruction sequence #1
> fe000258:   fc 60 68 28     fsub    f3,f0,f13<<<  Instruction sequence #2
> fe00025c:   74 60 00 08     andis.  r0,r3,8
> fe000260:   3c 80 00 01     lis r4,1
> fe000264:   fc 40 18 18     frsp    f2,f3
> fe000268:   fc 20 10 90     fmr f1,f2
> fe00026c:   fc 00 08 1e     fctiwz  f0,f1
> fe000270:   d8 01 00 10     stfd    f0,16(r1)
> fe000274:   80 e1 00 14     lwz r7,20(r1)
> fe000278:   98 e4 8f 0d     stb r7,-28915(r4)
> fe00027c:   41 82 00 c8     beq-    fe000344
>
> Instruction sequence #1 has been combined into a single equivalent instruction.  Instruction sequence #2 moved.  Register usage is also different but equivalent.
>
> Ron McCall