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

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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
This commit is contained in:
Aaron Sawdey 2019-07-02 13:51:23 -05:00
parent e2790e1eab
commit 02e3025e17
2 changed files with 37 additions and 0 deletions
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36
gcc/doc/md.texi
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@ -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

1
gcc/optabs.def
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@ -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")