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[doc patch] clarify what can appear in SET_DEST
- From: Steven Bosscher <stevenb at suse dot de>
- To: gcc-patches at gcc dot gnu dot org
- Cc: rth at redhat dot com
- Date: Tue, 4 Jan 2005 00:19:11 +0100
- Subject: [doc patch] clarify what can appear in SET_DEST
- Organization: SUSE Labs
Hi,
This is a doc patch to clarify what can appear as the target of a
SET rtx, according to my understanding of a brief explanation by
rth on IRC. I figured maybe other people could have understanding
it too, so let's update the docs now. Not sure it the patch is
correct, so CC'ing rth :-)
OK?
If this is correct, I'll also prepare patches for sched-deps.c and
df.c, where we do accept a SIGN_EXTRACT on the lhs of a set.
Gr.
Steven
* doc/rtl.texi: A ZERO_EXTRACT doesn't need a subreg. A
SIGN_EXTRACT can not be used as a lhs of a SET.
Index: doc/rtl.texi
===================================================================
RCS file: /cvs/gcc/gcc/gcc/doc/rtl.texi,v
retrieving revision 1.78
diff -u -r1.78 rtl.texi
--- doc/rtl.texi 17 Nov 2004 23:15:06 -0000 1.78
+++ doc/rtl.texi 3 Jan 2005 23:11:16 -0000
@@ -2365,10 +2365,11 @@
the mode of the register, the rest of the register can be changed in
an undefined way.
-If @var{lval} is a @code{strict_low_part} or @code{zero_extract}
-of a @code{subreg}, then the part of the register specified by the
+If @var{lval} is a @code{strict_low_part} of a subreg, or a
+@code{zero_extract}, then the part of the register specified by the
machine mode of the @code{subreg} is given the value @var{x} and
-the rest of the register is not changed.
+the rest of the register is not changed. Note that @code{sign_extract}
+can not appear in @var{lval}.
If @var{lval} is @code{(cc0)}, it has no machine mode, and @var{x} may
be either a @code{compare} expression or a value that may have any mode.