[AMDGPU] Add switch to enable architected SGPRs.

[foad]

LGTM.

llvm/lib/Target/AMDGPU/AMDGPU.td

872

Nit: I'd prefer a better description, but I don't have a suggestion. I've never really understood what "architected" is supposed to mean.

llvm/lib/Target/AMDGPU/AMDGPU.td

 >;
 
 def FeatureArchitectedFlatScratch : SubtargetFeature<"architected-flat-scratch",
   "HasArchitectedFlatScratch",
   "true",
   "Flat Scratch register is a readonly SPI initialized architected register"
 >;
 
+def FeatureArchitectedSGPRs : SubtargetFeature<"architected-sgprs",
+  "HasArchitectedSGPRs",
+  "true",
+  "Enable the architected SGPRs"
+>;
+
 // Dummy feature used to disable assembler instructions.
 def FeatureDisable : SubtargetFeature<"",
   "FeatureDisable","true",
   "Dummy feature to disable assembler instructions"
 >;
 
 class GCNSubtargetFeatureGeneration <string Value,
                                      string FeatureName,

llvm/lib/Target/AMDGPU/GCNSubtarget.h

protected:
   bool HasNoDataDepHazard = false;
   bool FlatAddressSpace = false;
   bool FlatInstOffsets = false;
   bool FlatGlobalInsts = false;
   bool FlatScratchInsts = false;
   bool ScalarFlatScratchInsts = false;
   bool HasArchitectedFlatScratch = false;
   bool EnableFlatScratch = false;
+  bool HasArchitectedSGPRs = false;
   bool AddNoCarryInsts = false;
   bool HasUnpackedD16VMem = false;
   bool LDSMisalignedBug = false;
   bool HasMFMAInlineLiteralBug = false;
   bool UnalignedBufferAccess = false;
   bool UnalignedDSAccess = false;
   bool HasPackedTID = false;
   bool ScalarizeGlobal = false;
public:
   bool flatScratchIsPointer() const {
     return getGeneration() >= AMDGPUSubtarget::GFX9;
   }
 
   /// \returns true if the flat_scratch register is initialized by the HW.
   /// In this case it is readonly.
   bool flatScratchIsArchitected() const { return HasArchitectedFlatScratch; }
 
+  /// \returns true if the architected SGPRs are enabled.
+  bool hasArchitectedSGPRs() const { return HasArchitectedSGPRs; }
+
   /// \returns true if the machine has merged shaders in which s0-s7 are
   /// reserved by the hardware and user SGPRs start at s8
   bool hasMergedShaders() const {
     return getGeneration() >= GFX9;
   }
 
   // \returns true if the target supports the pre-NGG legacy geometry path.
   bool hasLegacyGeometry() const { return getGeneration() < GFX11; }