AMDGPU: Make LDS_DIRECT an artifical register

[rampitec]

LGTM

[arsenm]

89b7091c28ad7879aea5d463930f54e7a9ba236e

llvm/lib/Target/AMDGPU/SIRegisterInfo.td

 def SGPR_NULL : SIReg<"null", 125>;
 
 def SRC_SHARED_BASE : SIReg<"src_shared_base", 235>;
 def SRC_SHARED_LIMIT : SIReg<"src_shared_limit", 236>;
 def SRC_PRIVATE_BASE : SIReg<"src_private_base", 237>;
 def SRC_PRIVATE_LIMIT : SIReg<"src_private_limit", 238>;
 def SRC_POPS_EXITING_WAVE_ID : SIReg<"src_pops_exiting_wave_id", 239>;
 
-def LDS_DIRECT : SIReg <"src_lds_direct", 254>;
+def LDS_DIRECT : SIReg <"src_lds_direct", 254> {
+  // There is no physical register corresponding to this. This is an
+  // encoding value in a source field, which will ultimately trigger a
+  // read from m0.
+  let isArtificial = 1;
+}
 
 def XNACK_MASK_LO : SIReg<"xnack_mask_lo", 104>;
 def XNACK_MASK_HI : SIReg<"xnack_mask_hi", 105>;
 
 def XNACK_MASK : RegisterWithSubRegs<"xnack_mask", [XNACK_MASK_LO, XNACK_MASK_HI]>,
                  DwarfRegAlias<XNACK_MASK_LO> {
   let Namespace = "AMDGPU";
   let SubRegIndices = [sub0, sub1];

 }
 
 def Pseudo_SReg_128 : RegisterClass<"AMDGPU", [v4i32, v2i64, v2f64], 32,
   (add PRIVATE_RSRC_REG)> {
   let isAllocatable = 0;
   let CopyCost = -1;
 }
 
-def LDS_DIRECT_CLASS : RegisterClass<"AMDGPU", [i32, f32, i16, f16, v2i16, v2f16], 32,
+def LDS_DIRECT_CLASS : RegisterClass<"AMDGPU", [i32], 32,
   (add LDS_DIRECT)> {
   let isAllocatable = 0;
   let CopyCost = -1;
 }
 
 // Subset of SReg_32 without M0 for SMRD instructions and alike.
 // See comments in SIInstructions.td for more info.
 def SReg_32_XM0_XEXEC : RegisterClass<"AMDGPU", [i32, f32, i16, f16, v2i16, v2f16, i1], 32,

 }
 
 // Register class for all scalar registers (SGPRs + Special Registers)
 def SReg_32 : RegisterClass<"AMDGPU", [i32, f32, i16, f16, v2i16, v2f16, i1], 32,
   (add SReg_32_XM0, M0_CLASS, EXEC_LO, EXEC_HI, SReg_32_XEXEC_HI)> {
   let AllocationPriority = 10;
 }
 
-def SRegOrLds_32 : RegisterClass<"AMDGPU", [i32, f32, i16, f16, v2i16, v2f16, i1], 32,
-  (add SReg_32_XM0, M0_CLASS, EXEC_LO, EXEC_HI, SReg_32_XEXEC_HI, LDS_DIRECT_CLASS)> {
+def SRegOrLds_32 : RegisterClass<"AMDGPU", [i32, f32, i16, f16, v2i16, v2f16], 32,
+  (add SReg_32, LDS_DIRECT_CLASS)> {
   let isAllocatable = 0;
 }
 
 def SGPR_64 : RegisterClass<"AMDGPU", [v2i32, i64, v2f32, f64, v4i16, v4f16], 32,
                             (add SGPR_64Regs)> {
   let CopyCost = 1;
   let AllocationPriority = 11;
 }