[Linux-ia64] Compiler warnings.

[Linux-ia64] Compiler warnings.

[Steffen Persvold]

Hi all,

For some time I've been compiling applications and kernels on IA64. 
Sometimes the assembler gives me warnings about "RAW dependencies" which 
makes me wonder about the quality of the gcc compiler. Is this something 
that should be paid attention to ?

Here's a warning (and not the only one) I get when I compile the latest 
2.4.18 patchset with gcc 2.96 (gcc version 2.96 20000731 (Debian GNU/Linux 
IA64 experimental)) :

gcc -D__KERNEL__ -I/usr/src/linux-2.4.18-020622/include 
-Wall -Wstrict-prototypes -Wno-trigraphs -g -O2 -fomit-frame-pointer 
-fno-strict-aliasing -fno-common -pipe  -ffixed-r13 
-mfixed-rangeñ0-f15,f32-f127 -falign-functions2 -mconstant-gp  
-DKBUILD_BASENAME=vmscan  -c -o vmscan.o vmscan.c
{standard input}: Assembler messages:
{standard input}:594: Warning: Use of 'st8' violates RAW dependency 'DTC' (data)
{standard input}:594: Warning: Only the first path encountering the conflict is reported
{standard input}:581: Warning: This is the location of the conflicting usage

I haven't tried the 3.0.1 compiler yet.

Thanks,
 -- 
  Steffen Persvold   | Scalable Linux Systems |   Try out the world's best
 mailto:sp@scali.com |  http://www.scali.com  | performing MPI implementation:
Tel: (+47) 2262 8950 |   Olaf Helsets vei 6   |      - ScaMPI 1.13.8 -
Fax: (+47) 2262 8951 |   N0621 Oslo, NORWAY   | >320MBytes/s and <4uS latency

Re: [Linux-ia64] Compiler warnings.

[Steffen Persvold]

On Sat, 22 Jun 2002, Steffen Persvold wrote:

> 
> Hi all,
> 
> For some time I've been compiling applications and kernels on IA64. 
> Sometimes the assembler gives me warnings about "RAW dependencies" which 
> makes me wonder about the quality of the gcc compiler. Is this something 
> that should be paid attention to ?
> 
> Here's a warning (and not the only one) I get when I compile the latest 
> 2.4.18 patchset with gcc 2.96 (gcc version 2.96 20000731 (Debian GNU/Linux 
> IA64 experimental)) :
> 
> gcc -D__KERNEL__ -I/usr/src/linux-2.4.18-020622/include 
> -Wall -Wstrict-prototypes -Wno-trigraphs -g -O2 -fomit-frame-pointer 
> -fno-strict-aliasing -fno-common -pipe  -ffixed-r13 
> -mfixed-rangeñ0-f15,f32-f127 -falign-functions2 -mconstant-gp  
> -DKBUILD_BASENAME=vmscan  -c -o vmscan.o vmscan.c
> {standard input}: Assembler messages:
> {standard input}:594: Warning: Use of 'st8' violates RAW dependency 'DTC' (data)
> {standard input}:594: Warning: Only the first path encountering the conflict is reported
> {standard input}:581: Warning: This is the location of the conflicting usage
> 
> I haven't tried the 3.0.1 compiler yet.
> 

I forgot, I've also been seeing "WAW dependencies" :

gcc -D__KERNEL__ -I/usr/src/linux-2.4.18-020622/include -Wall 
-Wstrict-prototypes -Wno-trigraphs -g -O2 -fomit-frame-pointer 
-fno-strict-aliasing -fno-common -pipe  -ffixed-r13 
-mfixed-rangeñ0-f15,f32-f127 -falign-functions2 -DMODULE -DMODVERSIONS 
-include /usr/src/linux-2.4.18-020622/include/linux/modversions.h -DDBG=0 
-DT3_JUMBO_RCV_RCB_ENTRY_COUNT%6 -DNICE_SUPPORT 
-DPCIX_TARGET_WORKAROUND=1 -DINCLUDE_TBI_SUPPORT -DINCLUDE_5701_AX_FIX=1 
-DKBUILD_BASENAMEµ7um  -c -o b57um.o b57um.c
{standard input}: Assembler messages:
{standard input}:13085: Warning: Use of 'cmp.ne' violates WAW dependency 'PR%, % in 1 - 15' (impliedf), specific resource number is 7
{standard input}:13085: Warning: Only the first path encountering the conflict is reported
{standard input}:13081: Warning: This is the location of the conflicting usage

Regards,
 -- 
  Steffen Persvold   | Scalable Linux Systems |   Try out the world's best
 mailto:sp@scali.com |  http://www.scali.com  | performing MPI implementation:
Tel: (+47) 2262 8950 |   Olaf Helsets vei 6   |      - ScaMPI 1.13.8 -
Fax: (+47) 2262 8951 |   N0621 Oslo, NORWAY   | >320MBytes/s and <4uS latency

Re: [Linux-ia64] Compiler warnings.

[David Mosberger]

>>>>> On Sat, 22 Jun 2002 11:53:40 +0200 (CEST), Steffen Persvold <sp@scali.com> said:

  Steffen> For some time I've been compiling applications and kernels
  Steffen> on IA64.  Sometimes the assembler gives me warnings about
  Steffen> "RAW dependencies" which makes me wonder about the quality
  Steffen> of the gcc compiler. Is this something that should be paid
  Steffen> attention to ?

I don't think you need to worry much here.  I keep a fairly close eye
on them and they tend to be all spurious messages due to the fact that
the assembler has an incomplete understanding of the code (and its
invariants).  The compiler should generate more directives to help the
assembler, but the code itself is generally correct.

I think gcc3.1 may be a bit better.  I only get 2 or 3 spurious
messages with it (apart from some that are due to inline asm, which
are harder to avoid).

	--david