This is the mail archive of the
gcc@gcc.gnu.org
mailing list for the GCC project.
Re: why are we not using const?
- From: Chris Lattner <clattner at apple dot com>
- To: Paolo Bonzini <paolo dot bonzini at lu dot unisi dot ch>
- Cc: "'Richard Guenther'" <richard dot guenther at gmail dot com>, "'Kaveh R. Ghazi'" <ghazi at caipclassic dot rutgers dot edu>, gdr at integrable-solutions dot net, gcc at gnu dot org, lopezibanez at gmail dot com, pinskia at physics dot uc dot edu, GCC Development <gcc at gcc dot gnu dot org>
- Date: Thu, 29 Jun 2006 09:39:18 -0700
- Subject: Re: why are we not using const?
- References: <014d01c69b83$27ba9c40$a501a8c0@CAM.ARTIMI.COM> <3E0FBACE-1C92-490B-9D1D-861D71BC28B1@apple.com> <44A3FDB6.5040001@lu.unisi.ch>
On Jun 29, 2006, at 9:20 AM, Paolo Bonzini wrote:
Well, G is known to escape anyway here. Even worse is this:
...
where there is not even the possibility to optimize *P1 in foo.
While compiling f1.c, the compiler does not even know that G
escapes and must assume the worse.
It's a different story for static variables or for -fwhole-program,
but then the compiler (as for the second load from *P1) can
optimize the third load anyway, independent of whether P1 is const
or not.
If the compiler has such a detailed knowledge of aliasing, why would
it have to depend on "const"? Assuming "const" were safe for the
compiler to use (which it isn't, obviously), it would only add value
if the compiler didn't have perfect knowledge of aliases already.
-Chris