On Thu, 23 Nov 2023, Jakub Jelinek wrote:
> On Thu, Nov 23, 2023 at 08:00:49AM +0000, Richard Biener wrote:
> > The following amends the cpymem documentation to mention that exact
> > overlap needs to be handled gracefully, also noting that the target
> > runtime is expected to behave the same way.
> >
> > OK?
> >
> > Thanks,
> > Richard.
> >
> > PR middle-end/32667
> > * md.texi (cpymem): Document that exact overlap of source
> > and destination needs to work. Mention the target runtime
> > may not treat this case as undefined.
>
> The first added sentence is ok, for the second see the spot
> Florian mentioned in the PR.
Like this?
Thanks,
Richard.
>From 93f4d22374ad2ea8bb5821083d2422c8b0a3313b Mon Sep 17 00:00:00 2001
From: Richard Biener <rguent...@suse.de>
Date: Thu, 23 Nov 2023 08:54:56 +0100
Subject: [PATCH] middle-end/32667 - document cpymem and memcpy exact overlap
requirement
To: gcc-patches@gcc.gnu.org
The following amends the cpymem documentation to mention that exact
overlap needs to be handled gracefully, also noting that the target
runtime is expected to behave the same way where -ffreestanding
docs mention the set of routines required.
PR middle-end/32667
* md.texi (cpymem): Document that exact overlap of source
and destination needs to work.
* standards.texi (ffreestanding): Mention memcpy is required
to handle the exact overlap case.
---
gcc/doc/md.texi | 5 +++--
gcc/doc/standards.texi | 4 +++-
2 files changed, 6 insertions(+), 3 deletions(-)
diff --git a/gcc/doc/md.texi b/gcc/doc/md.texi
index df6725ffc9c..87e1c9ed20e 100644
--- a/gcc/doc/md.texi
+++ b/gcc/doc/md.texi
@@ -6915,8 +6915,9 @@ individually copied data units in the block.
The @code{cpymem@var{m}} patterns need not give special consideration
to the possibility that the source and destination strings might
-overlap. These patterns are used to do inline expansion of
-@code{__builtin_memcpy}.
+overlap. An exeption is the case where source and destination are
+equal, this case needs to be handled correctly.
+These patterns are used to do inline expansion of @code{__builtin_memcpy}.
@cindex @code{movmem@var{m}} instruction pattern
@item @samp{movmem@var{m}}
diff --git a/gcc/doc/standards.texi b/gcc/doc/standards.texi
index 4eb43f14f90..6eebb9426f3 100644
--- a/gcc/doc/standards.texi
+++ b/gcc/doc/standards.texi
@@ -184,7 +184,9 @@ GNU C library). @xref{Standard Libraries,,Standard
Libraries}.
Most of the compiler support routines used by GCC are present in
@file{libgcc}, but there are a few exceptions. GCC requires the
freestanding environment provide @code{memcpy}, @code{memmove},
-@code{memset} and @code{memcmp}.
+@code{memset} and @code{memcmp}. Contrary to the standards
+covering @code{memcpy} GCC expects the case of an exact overlap
+of source and destination to work and not invoke undefined behavior.
Finally, if @code{__builtin_trap} is used, and the target does
not implement the @code{trap} pattern, then GCC emits a call
to @code{abort}.
--
2.35.3
