ac: add support for gl_HelperInvocation

Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>

src/amd/common/ac_nir_to_llvm.c

@@ -3915,6 +3915,17 @@ static void emit_discard(struct ac_nir_context *ctx,
 	ac_build_kill_if_false(&ctx->ac, cond);
 }
 
+static LLVMValueRef
+visit_load_helper_invocation(struct ac_nir_context *ctx)
+{
+	LLVMValueRef result = ac_build_intrinsic(&ctx->ac,
+						 "llvm.amdgcn.ps.live",
+						 ctx->ac.i1, NULL, 0,
+						 AC_FUNC_ATTR_READNONE);
+	result = LLVMBuildNot(ctx->ac.builder, result, "");
+	return LLVMBuildSExt(ctx->ac.builder, result, ctx->ac.i32, "");
+}
+
 static LLVMValueRef
 visit_load_local_invocation_index(struct nir_to_llvm_context *ctx)
 {
@@ -4354,6 +4365,9 @@ static void visit_intrinsic(struct ac_nir_context *ctx,
 	case nir_intrinsic_load_front_face:
 		result = ctx->abi->front_face;
 		break;
+	case nir_intrinsic_load_helper_invocation:
+		result = visit_load_helper_invocation(ctx);
+		break;
 	case nir_intrinsic_load_instance_id:
 		result = ctx->abi->instance_id;
 		break;