From 0c5f3c8d7d77307d79c6f764ef62ce6ffb3bc9e8 Mon Sep 17 00:00:00 2001 From: pbrook Date: Tue, 4 Nov 2008 13:17:17 +0000 Subject: Mention output overlaps. git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5619 c046a42c-6fe2-441c-8c8c-71466251a162 --- tcg/README | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'tcg/README') diff --git a/tcg/README b/tcg/README index 7e7c06b41c..bdb44dfd3b 100644 --- a/tcg/README +++ b/tcg/README @@ -390,6 +390,11 @@ GCC like constraints are used to define the constraints of every 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. -- cgit v1.2.1