From: "Meissner, Michael" <michael.meissner@amd.com>
To: zneda@ce.aut.ac.ir, gnu@gnu.org, gcc-help@gcc.gnu.org
Cc: neda.zf@gmail.com
Subject: RE: Hazard Detection
Date: Tue, 12 Dec 2006 18:31:00 -0000 [thread overview]
Message-ID: <6096959DEF5C9447A6BF80BDC7EB9EDC02A44E66@SBOSEXMB1.amd.com> (raw)
In-Reply-To: <40970.192.168.1.13.1165934653.squirrel@ce.aut.ac.ir>
> -----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.
next prev parent reply other threads:[~2006-12-12 18:31 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-12-12 14:37 zneda
2006-12-12 18:31 ` Meissner, Michael [this message]
2006-12-12 23:22 ` Ian Lance Taylor
2006-12-12 14:52 zneda
2006-12-12 14:56 zneda
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