Re: [PATCH] PR target/105325, Make load/cmp fusion know about prefixed loads

[Michael Meissner <meissner@linux.ibm.com>]

On Thu, Mar 23, 2023 at 04:10:22PM +0800, Kewen.Lin wrote:
> Hi Mike,
> 
> Thanks for fixing this, some minor comments are inlined below.
> 
> on 2023/3/22 07:53, Michael Meissner wrote:
> > The issue with the bug is the power10 load GPR + cmpi -1/0/1 fusion
> > optimization generates illegal assembler code.
> > 
> > Ultimately the code was dying because the fusion load + compare -1/0/1 patterns
> > did not handle the possibility that the load might be prefixed.
> > 
> > The main cause is the constraints for the individual loads in the fusion did not
> > match the machine.  In particular, LWA is a ds format instruction when it is
> > unprefixed.  The code did not also set the prefixed attribute correctly.
> > 
> > This patch rewrites the genfusion.pl script so that it will have more accurate
> > constraints for the LWA and LD instructions (which are DS instructions).  The
> > updated genfusion.pl was then run to update fusion.md.  Finally, the code for
> > the "prefixed" attribute is modified so that it considers load + compare
> > immediate patterns to be like the normal load insns in checking whether
> > operand[1] is a prefixed instruction.
> > 
> > I have tested this patch on a little endian power10 system, on a little endian
> > power9 system, and a big endian power8 system (both -m32 and -m64 tested on
> > BE).  There were no regressions, can I check this into the trunk?
> > 
> > The same patch applies to the gcc-12 and gcc-11 branches.  Can I check this
> > patch into those branches also after a burn-in period?
> > 
> > 2023-03-21   Michael Meissner  <meissner@linux.ibm.com>
> >              Aaron Sawdey  <acsawdey@linux.ibm.com>
> > 
> > gcc/
> > 
> > 	PR target/105325
> > 	* gcc/config/rs6000/genfusion.pl (gen_ld_cmpi_p10): Improve generation
> > 	of the ld and lwa instructions which use the DS encoding instead of D.
> > 	Use the YZ constraint for these loads.	Handle prefixed loads better.
> > 	Set the sign_extend attribute as appropriate.
> > 	* gcc/config/rs6000/fusion.md: Regenerate.
> > 	* gcc/config/rs6000/rs6000.md (prefixed attribute): Add fused_load_cmpi
> > 	instructions to the list of instructions that might have a prefixed load
> > 	instruction.
> > 
> > gcc/testsuite/
> > 
> > 	PR target/105325
> > 	* g++.target/powerpc/pr105325.C: New test.
> > 	* gcc.target/powerpc/fusion-p10-ldcmpi.c: Adjust insn counts.
> > ---
> >  gcc/config/rs6000/genfusion.pl                | 26 ++++++++++++++++---
> >  gcc/config/rs6000/fusion.md                   | 17 +++++++-----
> >  gcc/config/rs6000/rs6000.md                   |  2 +-
> >  gcc/testsuite/g++.target/powerpc/pr105325.C   | 24 +++++++++++++++++
> >  .../gcc.target/powerpc/fusion-p10-ldcmpi.c    |  4 +--
> >  5 files changed, 59 insertions(+), 14 deletions(-)
> >  create mode 100644 gcc/testsuite/g++.target/powerpc/pr105325.C
> > 
> > diff --git a/gcc/config/rs6000/genfusion.pl b/gcc/config/rs6000/genfusion.pl
> > index e4db352e0ce..4f367cadc52 100755
> > --- a/gcc/config/rs6000/genfusion.pl
> > +++ b/gcc/config/rs6000/genfusion.pl
> > @@ -56,7 +56,7 @@ sub mode_to_ldst_char
> >  sub gen_ld_cmpi_p10
> >  {
> >      my ($lmode, $ldst, $clobbermode, $result, $cmpl, $echr, $constpred,
> > -	$mempred, $ccmode, $np, $extend, $resultmode);
> > +	$mempred, $ccmode, $np, $extend, $resultmode, $constraint);
> >    LMODE: foreach $lmode ('DI','SI','HI','QI') {
> >        $ldst = mode_to_ldst_char($lmode);
> >        $clobbermode = $lmode;
> > @@ -71,21 +71,34 @@ sub gen_ld_cmpi_p10
> >        CCMODE: foreach $ccmode ('CC','CCUNS') {
> >  	  $np = "NON_PREFIXED_D";
> >  	  $mempred = "non_update_memory_operand";
> > +	  $constraint = "m";
> 
> The three assignments on $np $mempred $constraint can be moved
> to place (a) (see below) and add one explicit assignment for
> $constraint at place (b), since for the condition ccmode eq 'CC',
> HI/SI/DI have their own settings (btw QI is skipped), these
> assignments for default value can be moved to else arm (for CCUNS).

...

> we have broken it into two different arms for SI and DI, this
> comment can be removed?

...

> 
> ... and this comment.
> 

I have fixed these issues and reposted the patch as:

| Date: Fri, 24 Mar 2023 19:06:35 -0400
| From: Michael Meissner <meissner@linux.ibm.com>
| Subject: [PATCH, V2] PR target/105325, Make load/cmp fusion know about prefixed load
| Message-ID: <ZB4s+1RqBNR49tj/@toto.the-meissners.org>

-- 
Michael Meissner, IBM
PO Box 98, Ayer, Massachusetts, USA, 01432
email: meissner@linux.ibm.com