diff options
| author | Richard Biener <rguenther@suse.de> | 2023-11-23 08:54:56 +0100 |
|---|---|---|
| committer | Richard Biener <rguenther@suse.de> | 2023-11-23 09:28:21 +0100 |
| commit | 7758cb4b53e8a33642709402ce582f769eb9fd18 (patch) | |
| tree | 09a86848b328f052ed664fbf4b8f921e0b14b328 /gcc | |
| parent | 6ce952188ab39e303e4f63e474b5cba83b5b12fd (diff) | |
| download | gcc-7758cb4b53e8a33642709402ce582f769eb9fd18.zip gcc-7758cb4b53e8a33642709402ce582f769eb9fd18.tar.gz gcc-7758cb4b53e8a33642709402ce582f769eb9fd18.tar.bz2 | |
middle-end/32667 - document cpymem and memcpy exact overlap requirement
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
* doc/md.texi (cpymem): Document that exact overlap of source
and destination needs to work.
* doc/standards.texi (ffreestanding): Mention memcpy is required
to handle the exact overlap case.
Diffstat (limited to 'gcc')
| -rw-r--r-- | gcc/doc/md.texi | 5 | ||||
| -rw-r--r-- | 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 df6725f..536ce99 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 exception 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 4eb43f1..6eebb94 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}. |