md.texi (reload_in/out): Document restrictions in predicates and constraints for...

        * doc/md.texi (reload_in/out): Document restrictions in predicates
        and constraints for these patterns.  Document empty string matching
        ALL_REGS.

From-SVN: r44134

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 216bba69fdbc814794ae6c7c05ed1122d55de240..dfe38acf835da5b32585a661bd5f3f1f45186c11 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2001-07-18  Richard Henderson  <rth@redhat.com>
+
+       * doc/md.texi (reload_in/out): Document restrictions in predicates
+       and constraints for these patterns.  Document empty string matching
+       ALL_REGS.
+
 2001-07-18  Rainer Orth  <ro@TechFak.Uni-Bielefeld.DE>
 
        * defaults.h (ASM_OUTPUT_WEAK_ALIAS): Check for ASM_WEAKEN_LABEL.

diff --git a/gcc/doc/md.texi b/gcc/doc/md.texi
index f1073aa5db384eba8a8a955eaac3aa2645216ce8..0b680cdfc49a13489345252dd49e0473c03fbca1 100644 (file)
--- a/gcc/doc/md.texi
+++ b/gcc/doc/md.texi
@@ -2076,6 +2076,17 @@ move between operand 0 and operand 1.  Operand 2 describes the scratch
 register.  See the discussion of the @code{SECONDARY_RELOAD_CLASS}
 macro in @pxref{Register Classes}.
 
+There are special restrictions on the form of the @code{match_operand}s
+used in these patterns.  First, only the predicate for the reload 
+operand is examined, i.e. @code{reload_in} examines operand 1, but not
+the predicates for operand 0 or 2.  Second, there may only be one
+alternative in the constraints.  Third, only a single register class
+letter may be used for the constraint; subsequent constraint letters
+are ignored.  As a special exception, an empty constraint string
+matches the @code{ALL_REGS} register class.  This may relieve ports
+of the burden of defining an @code{ALL_REGS} constraint letter just
+for these patterns.
+
 @cindex @code{movstrict@var{m}} instruction pattern
 @item @samp{movstrict@var{m}}
 Like @samp{mov@var{m}} except that if operand 0 is a @code{subreg}