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Re: x86 inc/dec on core2

From: "Vladimir N. Makarov" <vmakarov at redhat dot com>
To: Mike Stump <mrs at apple dot com>
Cc: GCC Development <gcc at gcc dot gnu dot org>
Date: Sun, 08 Apr 2007 17:39:23 -0400
Subject: Re: x86 inc/dec on core2
References: <7342950E-0B89-4620-B02D-2DAC0EFF63DB@apple.com>

Mike Stump wrote:

I was wondering, if:
  /* X86_TUNE_USE_INCDEC */
  ~(m_PENT4 | m_NOCONA | m_CORE2 | m_GENERIC),
is correct. Should it be:
  /* X86_TUNE_USE_INCDEC */
  ~(m_PENT4 | m_NOCONA | m_GENERIC),
?

In the original patch in:

2006-11-18 Vladimir Makarov <vmakarov@redhat.com>

* doc/invoke.texi (core2): Add item.

it wasn't present, but in the checked in patch in r118973, it is:
$ svn diff -r118972:118973 i386.c | grep incdec
-const int x86_use_incdec = ~(m_PENT4 | m_NOCONA | m_GENERIC);
+const int x86_use_incdec = ~(m_PENT4 | m_NOCONA | m_CORE2 | m_GENERIC);

It is probably a typo. I did several changes after original patch submission because people asked me to benhmark several parameters.

Core2 really should generate INC/DEC because it results in smaller programs (as I remember about 0.4% and 0.1% correspondingly for SPECINT2000 and SPECFP2000) and I definitely remeber a bit better code too.

I looked around for a discussion on this, and didn't find it.

Thanks?

References:
- x86 inc/dec on core2
  - From: Mike Stump

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