Richard Guenther - Re: Memory partitioning considered harmful (!?) (original) (raw)

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• From: Richard Guenther
• To: Tobias Schlüter
• Cc: François-Xavier Coudert , Diego Novillo , gcc-patches , Fortran List , Daniel Berlin
• Date: Thu, 8 Feb 2007 18🔞43 +0100 (CET)
• Subject: Re: Memory partitioning considered harmful (!?)
• References: <19c433eb0702080814k3f93c15r946cfa7811e2e5f0@mail.gmail.com> <Pine.LNX.4.64.0702081737120.3994@zhemvz.fhfr.qr> <45CB5A5C.8040009@physik.uni-muenchen.de>

On Thu, 8 Feb 2007, Tobias Schlüter wrote:

Richard Guenther wrote:

The other thing is to use by-value argument passing conventions for internal intrinsics wherever possible so that a

write (,) a

does not make 'a' addressable. This is what makes fatigue so sensitive to the partitioning choices - we have an addressable induction variable and miss loop invariant motion of sin() and cos() calls if the memory tag for the induction variable is coalesced with the wrong things. The induction variable only has a memory tag because it is marked addressable and this is only due to the fact that fatigue re-uses it in an I/O statement (like the one quoted above) later in the function.

Is there no finer-grained control available which says "this variable's address is taken, but it's not written to"? This seems useful for both passing structures in C code and INTENT(IN) arguments in Fortran code (where we can't use different calling conventions due to compatibility with legacy code).

No, the middle-end does not (yet) have support for such. It's not impossible to add, though.

Richard.

-- Richard Guenther rguenther@suse.de Novell / SUSE Labs

• References:
  • Re: Memory partitioning considered harmful (!?)
    * From: François-Xavier Coudert
  • Re: Memory partitioning considered harmful (!?)
    * From: Richard Guenther
  • Re: Memory partitioning considered harmful (!?)
    * From: Tobias Schlüter