optabs.def (movmem_optab): Add movmem back for memmove().

2019-07-02  Aaron Sawdey  <acsawdey@linux.ibm.com>

	* optabs.def (movmem_optab): Add movmem back for memmove().
	* doc/md.texi: Add description of movmem pattern for overlapping move.

From-SVN: r272946

2 files changed, 37 insertions, 0 deletions

diff --git a/gcc/doc/md.texi b/gcc/doc/md.texi
index 3f9d545..b1fcc38 100644
--- a/gcc/doc/md.texi
+++ b/gcc/doc/md.texi
@@ -6237,6 +6237,42 @@ to the possibility that the source and destination strings might
 overlap. These patterns are used to do inline expansion of
 @code{__builtin_memcpy}.
 
+@cindex @code{movmem@var{m}} instruction pattern
+@item @samp{movmem@var{m}}
+Block move instruction.  The destination and source blocks of memory
+are the first two operands, and both are @code{mem:BLK}s with an
+address in mode @code{Pmode}.
+
+The number of bytes to copy is the third operand, in mode @var{m}.
+Usually, you specify @code{Pmode} for @var{m}.  However, if you can
+generate better code knowing the range of valid lengths is smaller than
+those representable in a full Pmode pointer, you should provide
+a pattern with a
+mode corresponding to the range of values you can handle efficiently
+(e.g., @code{QImode} for values in the range 0--127; note we avoid numbers
+that appear negative) and also a pattern with @code{Pmode}.
+
+The fourth operand is the known shared alignment of the source and
+destination, in the form of a @code{const_int} rtx.  Thus, if the
+compiler knows that both source and destination are word-aligned,
+it may provide the value 4 for this operand.
+
+Optional operands 5 and 6 specify expected alignment and size of block
+respectively.  The expected alignment differs from alignment in operand 4
+in a way that the blocks are not required to be aligned according to it in
+all cases. This expected alignment is also in bytes, just like operand 4.
+Expected size, when unknown, is set to @code{(const_int -1)}.
+
+Descriptions of multiple @code{movmem@var{m}} patterns can only be
+beneficial if the patterns for smaller modes have fewer restrictions
+on their first, second and fourth operands.  Note that the mode @var{m}
+in @code{movmem@var{m}} does not impose any restriction on the mode of
+individually copied data units in the block.
+
+The @code{movmem@var{m}} patterns must correctly handle the case where
+the source and destination strings overlap. These patterns are used to
+do inline expansion of @code{__builtin_memmove}.
+
 @cindex @code{movstr} instruction pattern
 @item @samp{movstr}
 String copy instruction, with @code{stpcpy} semantics.  Operand 0 is
diff --git a/gcc/optabs.def b/gcc/optabs.def
index 03a08da..4ffd0f3 100644
--- a/gcc/optabs.def
+++ b/gcc/optabs.def
@@ -257,6 +257,7 @@ OPTAB_D (cmpmem_optab, "cmpmem$a")
 OPTAB_D (cmpstr_optab, "cmpstr$a")
 OPTAB_D (cmpstrn_optab, "cmpstrn$a")
 OPTAB_D (cpymem_optab, "cpymem$a")
+OPTAB_D (movmem_optab, "movmem$a")
 OPTAB_D (setmem_optab, "setmem$a")
 OPTAB_D (strlen_optab, "strlen$a")