[AMDGPU] Fix indirect dst bug for non-sgpr index (#98907)

When emitting indirect dst, if the idx is not SGPR there was a bug that
didn't
take into account that the subregister might be different from
computeIndirectRegAndOffset.

Author: dstutt

llvm/lib/Target/AMDGPU/SIISelLowering.cpp

@@ -4814,14 +4814,14 @@ static MachineBasicBlock *emitIndirectDst(MachineInstr &MI,
         .addReg(PhiReg)
         .add(*Val)
         .addReg(SGPRIdxReg)
-        .addImm(AMDGPU::sub0);
+        .addImm(SubReg);
   } else {
     const MCInstrDesc &MovRelDesc = TII->getIndirectRegWriteMovRelPseudo(
         TRI.getRegSizeInBits(*VecRC), 32, false);
     BuildMI(*LoopBB, InsPt, DL, MovRelDesc, Dst)
         .addReg(PhiReg)
         .add(*Val)
-        .addImm(AMDGPU::sub0);
+        .addImm(SubReg);
   }
 
   MI.eraseFromParent();

llvm/test/CodeGen/AMDGPU/indirect-addressing-si.ll

@@ -543,6 +543,24 @@ bb8:                                              ; preds = %bb2
   ret void
 }
 
+; GCN-LABEL: {{^}}insert_or_disj_index:
+; GCN: v_mov_b32_e32 v[[#VIDX:]], 0
+
+; MOVREL: s_mov_b32 m0, s{{[0-9]+}}
+; MOVREL: v_movreld_b32_e32 v[[#VIDX + 1]], v{{[0-9]+}}
+
+; IDXMODE: s_set_gpr_idx_on s{{[0-9]+}}, gpr_idx(DST)
+; IDXMODE: v_mov_b32_e32 v[[#VIDX + 1]], v{{[0-9]+}}
+; IDXMODE: s_set_gpr_idx_off
+define amdgpu_cs void @insert_or_disj_index(ptr addrspace(1) %out, ptr addrspace(4) %in, i32 %val, <4 x i32> inreg %desc, i32 inreg %A) {
+entry:
+  %idx = call i32 @llvm.amdgcn.raw.buffer.load.i32(<4 x i32> %desc, i32 %A, i32 0, i32 0)
+  %off = or disjoint i32 %idx, 1
+  %v = insertelement <16 x i32> zeroinitializer, i32 %val, i32 %off
+  store <16 x i32> %v, ptr addrspace(1) %out
+  ret void
+}
+
 declare i32 @llvm.amdgcn.workitem.id.x() #1
 declare void @llvm.amdgcn.s.barrier() #2