[SystemZ] Enable long displacement constraints for inline ASM operands

This enables use of the 'S' constraint for inline ASM operands on
SystemZ, which allows for a memory reference with a signed 20-bit
immediate displacement. This patch includes corresponding documentation
and test case updates.

I've changed the 'T' constraint to match the new behavior for 'S', as
'T' also uses a long displacement (though index constraints are still
not implemented). I also changed 'm' to match the behavior for 'S' as
this will allow for a wider range of displacements for 'm', though
correct me if that's not the right decision.

Author: colpell
Differential Revision: http://reviews.llvm.org/D21097

llvm-svn: 272266

1 files changed, 4 insertions, 2 deletions

diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst
index d9de43e3e4d..1b0d0cf5e6d 100644
--- a/llvm/docs/LangRef.rst
+++ b/llvm/docs/LangRef.rst
@@ -3590,8 +3590,10 @@ SystemZ:
 - ``K``: An immediate signed 16-bit integer.
 - ``L``: An immediate signed 20-bit integer.
 - ``M``: An immediate integer 0x7fffffff.
-- ``Q``, ``R``, ``S``, ``T``: A memory address operand, treated the same as
-  ``m``, at the moment.
+- ``Q``, ``R``: A memory address operand with a base address and a 12-bit
+  immediate unsigned displacement.
+- ``S``, ``T``: A memory address operand with a base address and a 20-bit
+  immediate signed displacement.
 - ``r`` or ``d``: A 32, 64, or 128-bit integer register.
 - ``a``: A 32, 64, or 128-bit integer address register (excludes R0, which in an
   address context evaluates as zero).