[SystemZ] Add support for z13 and its vector facility

This patch adds support for the z13 architecture type.  For compatibility
with GCC, a pair of options -mvx / -mno-vx can be used to selectively
enable/disable use of the vector facility.

When the vector facility is present, we default to the new vector ABI.
This is characterized by two major differences:
- Vector types are passed/returned in vector registers
  (except for unnamed arguments of a variable-argument list function).
- Vector types are at most 8-byte aligned.

The reason for the choice of 8-byte vector alignment is that the hardware
is able to efficiently load vectors at 8-byte alignment, and the ABI only
guarantees 8-byte alignment of the stack pointer, so requiring any higher
alignment for vectors would require dynamic stack re-alignment code.

However, for compatibility with old code that may use vector types, when
*not* using the vector facility, the old alignment rules (vector types
are naturally aligned) remain in use.

These alignment rules are not only implemented at the C language level,
but also at the LLVM IR level.  This is done by selecting a different
DataLayout string depending on whether the vector ABI is in effect or not.

Based on a patch by Richard Sandiford.

llvm-svn: 236531

1 files changed, 8 insertions, 0 deletions

diff --git a/clang/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index 27e6427d0d4..3f4c3171332 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -1442,6 +1442,14 @@ static void getSystemZTargetFeatures(const ArgList &Args,
     else
       Features.push_back("-transactional-execution");
   }
+  // -m(no-)vx overrides use of the vector facility.
+  if (Arg *A = Args.getLastArg(options::OPT_mvx,
+                               options::OPT_mno_vx)) {
+    if (A->getOption().matches(options::OPT_mvx))
+      Features.push_back("+vector");
+    else
+      Features.push_back("-vector");
+  }
 }
 
 static const char *getX86TargetCPU(const ArgList &Args,