[AArch64] Static (de)allocation of SVE stack objects.

Adds support to AArch64FrameLowering to allocate fixed-stack SVE objects.

The focus of this patch is purely to allow the stack frame to
allocate/deallocate space for scalable SVE objects. More dynamic
allocation (at compile-time, i.e. determining placement of SVE objects
on the stack), or resolving frame-index references that include
scalable-sized offsets, are left for subsequent patches.

SVE objects are allocated in the stack frame as a separate region below
the callee-save area, and above the alignment gap. This is done so that
the SVE objects can be accessed directly from the FP at (runtime)
VL-based offsets to benefit from using the VL-scaled addressing modes.

The layout looks as follows:

     +-------------+
     | stack arg   |   
     +-------------+
     | Callee Saves|
     |   X29, X30  |       (if available)
     |-------------| <- FP (if available)
     |     :       |   
     |  SVE area   |   
     |     :       |   
     +-------------+
     |/////////////| alignment gap.
     |     :       |   
     | Stack objs  |
     |     :       |   
     +-------------+ <- SP after call and frame-setup

SVE and non-SVE stack objects are distinguished using different
StackIDs. The offsets for objects with TargetStackID::SVEVector should be
interpreted as purely scalable offsets within their respective SVE region.

Reviewers: thegameg, rovka, t.p.northover, efriedma, rengolin, greened

Reviewed By: efriedma

Differential Revision: https://reviews.llvm.org/D61437

llvm-svn: 373585

1 files changed, 2 insertions, 0 deletions

diff --git a/llvm/lib/Target/AMDGPU/SIFrameLowering.cpp b/llvm/lib/Target/AMDGPU/SIFrameLowering.cpp
index 22f035e7f3e..ed07ed100a1 100644
--- a/llvm/lib/Target/AMDGPU/SIFrameLowering.cpp
+++ b/llvm/lib/Target/AMDGPU/SIFrameLowering.cpp
@@ -673,6 +673,8 @@ bool SIFrameLowering::isSupportedStackID(TargetStackID::Value ID) const {
   case TargetStackID::NoAlloc:
   case TargetStackID::SGPRSpill:
     return true;
+  case TargetStackID::SVEVector:
+    return false;
   }
   llvm_unreachable("Invalid TargetStackID::Value");
 }