[AMDGPU] Mark workgroup_id intrinsics always uniform (#102042)

Author: rampitec

llvm/lib/Target/AMDGPU/AMDGPUSearchableTables.td

@@ -378,3 +378,6 @@ def : AlwaysUniform<int_amdgcn_icmp>;
 def : AlwaysUniform<int_amdgcn_fcmp>;
 def : AlwaysUniform<int_amdgcn_ballot>;
 def : AlwaysUniform<int_amdgcn_if_break>;
+def : AlwaysUniform<int_amdgcn_workgroup_id_x>;
+def : AlwaysUniform<int_amdgcn_workgroup_id_y>;
+def : AlwaysUniform<int_amdgcn_workgroup_id_z>;

llvm/test/Analysis/UniformityAnalysis/AMDGPU/always_uniform.ll

@@ -79,11 +79,38 @@ define void @no_divergent_args_if_inreg(i32 inreg %i32, i1 inreg %i1) {
  ret void
 }
 
+; CHECK-LABEL: for function 'workgroup_id_x':
+; CHECK: ALL VALUES UNIFORM
+define void @workgroup_id_x(ptr addrspace(1) inreg %out) {
+  %result = call i32 @llvm.amdgcn.workgroup.id.x()
+  store i32 %result, ptr addrspace(1) %out, align 4
+  ret void
+}
+
+; CHECK-LABEL: for function 'workgroup_id_y':
+; CHECK: ALL VALUES UNIFORM
+define void @workgroup_id_y(ptr addrspace(1) inreg %out) {
+  %result = call i32 @llvm.amdgcn.workgroup.id.y()
+  store i32 %result, ptr addrspace(1) %out, align 4
+  ret void
+}
+
+; CHECK-LABEL: for function 'workgroup_id_z':
+; CHECK: ALL VALUES UNIFORM
+define void @workgroup_id_z(ptr addrspace(1) inreg %out) {
+  %result = call i32 @llvm.amdgcn.workgroup.id.z()
+  store i32 %result, ptr addrspace(1) %out, align 4
+  ret void
+}
+
 declare i32 @llvm.amdgcn.workitem.id.x() #0
 declare i32 @llvm.amdgcn.readfirstlane(i32) #0
 declare i64 @llvm.amdgcn.icmp.i32(i32, i32, i32) #1
 declare i64 @llvm.amdgcn.fcmp.i32(float, float, i32) #1
 declare i64 @llvm.amdgcn.ballot.i32(i1) #1
+declare i32 @llvm.amdgcn.workgroup.id.x() #0
+declare i32 @llvm.amdgcn.workgroup.id.y() #0
+declare i32 @llvm.amdgcn.workgroup.id.z() #0
 
 attributes #0 = { nounwind readnone }
 attributes #1 = { nounwind readnone convergent }