diff --git a/gcc/doc/md.texi b/gcc/doc/md.texi
index df6725ffc9c..536ce997f01 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 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}.