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Diffstat (limited to 'gcc/md.texi')
| -rw-r--r-- | gcc/md.texi | 10 |
1 files changed, 9 insertions, 1 deletions
diff --git a/gcc/md.texi b/gcc/md.texi index 8ac4d102f30..e9d4e83e637 100644 --- a/gcc/md.texi +++ b/gcc/md.texi @@ -1949,7 +1949,14 @@ The @samp{cmp@var{m}} patterns should be used instead. @item @samp{movstr@var{m}} Block move instruction. The addresses of the destination and source strings are the first two operands, and both are in mode @code{Pmode}. + The number of bytes to move is the third operand, in mode @var{m}. +Usually, you specify @code{word_mode} for @var{m}. However, if you can +generate better code knowing the range of valid lengths is smaller than +those representable in a full word, 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{word_mode}. 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 @@ -1969,7 +1976,8 @@ that the source and destination strings might overlap. @item @samp{clrstr@var{m}} Block clear instruction. The addresses of the destination string is the first operand, in mode @code{Pmode}. The number of bytes to clear is -the second operand, in mode @var{m}. +the second operand, in mode @var{m}. See @samp{movstr@var{m}} for +a discussion of the choice of mode. The third operand is the known alignment of the destination, in the form of a @code{const_int} rtx. Thus, if the compiler knows that the |