* Hazard Detection
@ 2006-12-12 14:37 zneda
2006-12-12 18:31 ` Meissner, Michael
0 siblings, 1 reply; 5+ messages in thread
From: zneda @ 2006-12-12 14:37 UTC (permalink / raw)
To: gnu, gcc-help; +Cc: neda.zf
Hi
I have a question: I compiled a program with gcc -mips1 ,
Compiler generate this list of instructions:
... .... ...
10b71c: 87a20018 lh v0,24(sp)
10b720: 00000000 nop
10b724: 144000b9 bnez v0,10ba0c
10b728: 0015ac03 sra s5,s5,0x10
... .... ...
but by a small change, some times in variables, (using same compiler
switches) compiler don't insert nop between load and branch and generates
this sequence of instructions:
... .... ...
10b754: 87a20018 lh v0,24(sp)
10b758: 144000b9 bnez v0,10ba40
10b75c: 0015ac03 sra s5,s5,0x10
... .... ...
would you please tell me the reason?
why doesn't compiler detect hazard always?
Thanks in advanced.
Neda Zolfaghari (zneda@aut.ac.ir)
^ permalink raw reply [flat|nested] 5+ messages in thread
* RE: Hazard Detection
2006-12-12 14:37 Hazard Detection zneda
@ 2006-12-12 18:31 ` Meissner, Michael
2006-12-12 23:22 ` Ian Lance Taylor
0 siblings, 1 reply; 5+ messages in thread
From: Meissner, Michael @ 2006-12-12 18:31 UTC (permalink / raw)
To: zneda, gnu, gcc-help; +Cc: neda.zf
> -----Original Message-----
> From: gcc-help-owner@gcc.gnu.org [mailto:gcc-help-owner@gcc.gnu.org]
On
> Behalf Of zneda@ce.aut.ac.ir
> Sent: Tuesday, December 12, 2006 9:44 AM
> To: gnu@gnu.org; gcc-help@gcc.gnu.org
> Cc: neda.zf@gmail.com
> Subject: Hazard Detection
>
> Hi
>
> I have a question: I compiled a program with gcc -mips1 ,
> Compiler generate this list of instructions:
> ... .... ...
> 10b71c: 87a20018 lh v0,24(sp)
> 10b720: 00000000 nop
> 10b724: 144000b9 bnez v0,10ba0c
> 10b728: 0015ac03 sra s5,s5,0x10
> ... .... ...
>
> but by a small change, some times in variables, (using same compiler
> switches) compiler don't insert nop between load and branch and
generates
> this sequence of instructions:
> ... .... ...
> 10b754: 87a20018 lh v0,24(sp)
> 10b758: 144000b9 bnez v0,10ba40
> 10b75c: 0015ac03 sra s5,s5,0x10
> ... .... ...
>
> would you please tell me the reason?
>
> why doesn't compiler detect hazard always?
>
> Thanks in advanced.
I haven't programmed in the MIPS for awhile, but when I did, GCC
expected the assembler to do the hazard detection (ie, if you
disassemble the object code, there should be a NOP between the lh and
the bnez if -mips1 was passed to the assembler. GCC used to have a
separate hazard detection pass many years ago, but it was removed when
GAS added the support.
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Hazard Detection
2006-12-12 18:31 ` Meissner, Michael
@ 2006-12-12 23:22 ` Ian Lance Taylor
0 siblings, 0 replies; 5+ messages in thread
From: Ian Lance Taylor @ 2006-12-12 23:22 UTC (permalink / raw)
To: Meissner, Michael; +Cc: zneda, gcc-help, neda.zf
"Meissner, Michael" <michael.meissner@amd.com> writes:
> I haven't programmed in the MIPS for awhile, but when I did, GCC
> expected the assembler to do the hazard detection (ie, if you
> disassemble the object code, there should be a NOP between the lh and
> the bnez if -mips1 was passed to the assembler. GCC used to have a
> separate hazard detection pass many years ago, but it was removed when
> GAS added the support.
gcc did get hazard detection added back in again, though, and gcc can
now generate the whole function in .set noreorder. See, e.g.,
mips_avoid_hazard in config/mips/mips.c.
I don't know what the original problem is here. It may be a bug, or
gcc may be in a mode in which it expects the assembler to insert the
nop, or it may be necessary to use an appropriate -march option, or it
may be something else entirely.
Ian
^ permalink raw reply [flat|nested] 5+ messages in thread
* Hazard Detection
@ 2006-12-12 14:52 zneda
0 siblings, 0 replies; 5+ messages in thread
From: zneda @ 2006-12-12 14:52 UTC (permalink / raw)
To: gcc-help; +Cc: neda.zf
Hi
I have a question: I compiled a program with  gcc
-mips1 ,
Compiler generate this list of instructions:
Â
... Â Â Â Â Â Â Â .... Â Â
     ...
 10b71c: Â
 87a20018    lh   Â
 v0,24(sp)
 10b720:   00000000  Â
nop
 10b724:   144000b9   bnez Â
 v0,10ba0c
 10b728:   0015ac03  Â
 sra    s5,s5,0x10
 ...  Â
     ....     Â
  ...
but by a small change, some times in
variables, (using same compiler
switches) compiler don't insert
 nop between load and branch and generates
this sequence of
instructions:
 ...      Â
 ....        ...
 10b754:   87a20018   lh   Â
 v0,24(sp)
 10b758:   144000b9  Â
bnez   v0,10ba40
 10b75c:   0015ac03
   sra    s5,s5,0x10
 ...
       ....   Â
    ...
would you please tell me the
reason?
why doesn't compiler detect hazard always?
Thanks in advanced.
Neda Zolfaghari (zneda@aut.ac.ir)
^ permalink raw reply [flat|nested] 5+ messages in thread
* Hazard Detection
@ 2006-12-12 14:56 zneda
0 siblings, 0 replies; 5+ messages in thread
From: zneda @ 2006-12-12 14:56 UTC (permalink / raw)
To: gcc-help; +Cc: neda.zf
Hi
I have a question:
I compiled a program with gcc -mips1 ,
Compiler
generate this list of instructions:
Â
     ...     Â
  ....      Â
    ...
 10b71c:  Â
 87a20018     lh   Â
   v0,24(sp)
 10b720:   Â
00000000 Â Â Â Â Â nop
 10b724:    144000b9   Â
 bnez   v0,10ba0c
 10b728:
   0015ac03      sra
     s5,s5,0x10
 ...  Â
        ....Â
         Â
    ...
but by a small change, some
times in variables, (using same compiler
switches) compiler don't
insert nop between load and
branch and generates
this sequence of
instructions:
 ...   Â
....         ...
10b754: Â Â Â 87a20018 Â Â Â lhÂ
      v0,24(sp)
10b758:
   144000b9    bnez  Â
v0,10ba40
10b75c: Â Â Â 0015ac03Â Â Â
sra       s5,s5,0x10
Â
...         Â
   ....      Â
     ...
would you please tell me
the reason?
why doesn't compiler detect hazard always?
Thanks in advanced.
Neda Zolfaghari (zneda@aut.ac.ir)
^ permalink raw reply [flat|nested] 5+ messages in thread
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2006-12-12 14:37 Hazard Detection zneda
2006-12-12 18:31 ` Meissner, Michael
2006-12-12 23:22 ` Ian Lance Taylor
2006-12-12 14:52 zneda
2006-12-12 14:56 zneda
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