[Qemu-devel] [5619] Mention output overlaps.

[Paul Brook]

Revision: 5619
          http://svn.sv.gnu.org/viewvc/?view=rev&root=qemu&revision=5619
Author:   pbrook
Date:     2008-11-04 13:17:17 +0000 (Tue, 04 Nov 2008)

Log Message:
-----------
Mention output overlaps.

Modified Paths:
--------------
    trunk/tcg/README

Modified: trunk/tcg/README
===================================================================
--- trunk/tcg/README    2008-11-04 12:33:21 UTC (rev 5618)
+++ trunk/tcg/README    2008-11-04 13:17:17 UTC (rev 5619)
@@ -390,6 +390,11 @@
 instruction. Memory constraints are not supported in this
 version. Aliases are specified in the input operands as for GCC.
 
+The same register may be used for both an input and an output, even when
+they are not explicitly aliased.  If an op expands to multiple target
+instructions then care must be taken to avoid clobbering input values.
+GCC style "early clobber" outputs are not currently supported.
+
 A target can define specific register or constant constraints. If an
 operation uses a constant input constraint which does not allow all
 constants, it must also accept registers in order to have a fallback.