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[Qemu-devel] [5619] Mention output overlaps.
From: |
Paul Brook |
Subject: |
[Qemu-devel] [5619] Mention output overlaps. |
Date: |
Tue, 04 Nov 2008 13:17:18 +0000 |
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.
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