[AMDGPU] Use subreg encoding instead of reassign

The HWEncoding for these 64 bit registers should be the same as as the
encoding for the previously defined low halves of the registers. So
reuse that value instead of repeating the assignment. NFC.

Reviewed By: foad

Differential Revision: https://reviews.llvm.org/D121391

Author: Sisyph

llvm/lib/Target/AMDGPU/SIRegisterInfo.td

@@ -189,7 +189,7 @@ def PC_REG : SIReg<"pc", 0>, DwarfRegNum<[16, 16]> {
 def VCC : RegisterWithSubRegs<"vcc", [VCC_LO, VCC_HI]> {
   let Namespace = "AMDGPU";
   let SubRegIndices = [sub0, sub1];
-  let HWEncoding = 106;
+  let HWEncoding = VCC_LO.HWEncoding;
 }
 
 defm EXEC_LO : SIRegLoHi16<"exec_lo", 126>, DwarfRegNum<[1, 1]>;
@@ -198,7 +198,7 @@ defm EXEC_HI : SIRegLoHi16<"exec_hi", 127>;
 def EXEC : RegisterWithSubRegs<"exec", [EXEC_LO, EXEC_HI]>, DwarfRegNum<[17, 1]> {
   let Namespace = "AMDGPU";
   let SubRegIndices = [sub0, sub1];
-  let HWEncoding = 126;
+  let HWEncoding = EXEC_LO.HWEncoding;
 }
 
 // 32-bit real registers, for MC only.
@@ -237,7 +237,7 @@ def XNACK_MASK :
     RegisterWithSubRegs<"xnack_mask", [XNACK_MASK_LO, XNACK_MASK_HI]> {
   let Namespace = "AMDGPU";
   let SubRegIndices = [sub0, sub1];
-  let HWEncoding = 104;
+  let HWEncoding = XNACK_MASK_LO.HWEncoding;
 }
 
 // Trap handler registers
@@ -247,7 +247,7 @@ defm TBA_HI : SIRegLoHi16<"tba_hi", 109>;
 def TBA : RegisterWithSubRegs<"tba", [TBA_LO, TBA_HI]> {
   let Namespace = "AMDGPU";
   let SubRegIndices = [sub0, sub1];
-  let HWEncoding = 108;
+  let HWEncoding = TBA_LO.HWEncoding;
 }
 
 defm TMA_LO : SIRegLoHi16<"tma_lo", 110>;
@@ -256,7 +256,7 @@ defm TMA_HI : SIRegLoHi16<"tma_hi", 111>;
 def TMA : RegisterWithSubRegs<"tma", [TMA_LO, TMA_HI]> {
   let Namespace = "AMDGPU";
   let SubRegIndices = [sub0, sub1];
-  let HWEncoding = 110;
+  let HWEncoding = TMA_LO.HWEncoding;
 }
 
 foreach Index = 0...15 in {