nir: Add nir_lower_halt_to_return

This is a lowering pass that was implemented by multiple drivers.

Reviewed-by: Mary Guillemard <mary@mary.zone>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33003>

src/compiler/nir/meson.build

@@ -175,6 +175,7 @@ else
   'nir_lower_global_vars_to_local.c',
   'nir_lower_goto_ifs.c',
   'nir_lower_gs_intrinsics.c',
+  'nir_lower_halt_to_return.c',
   'nir_lower_helper_writes.c',
   'nir_lower_load_const_to_scalar.c',
   'nir_lower_locals_to_regs.c',

src/compiler/nir/nir.h

@@ -5848,6 +5848,8 @@ typedef enum {
 
 bool nir_lower_gs_intrinsics(nir_shader *shader, nir_lower_gs_intrinsics_flags options);
 
+bool nir_lower_halt_to_return(nir_shader *nir);
+
 bool nir_lower_tess_coord_z(nir_shader *shader, bool triangles);
 
 typedef struct nir_lower_task_shader_options {

src/compiler/nir/nir_lower_halt_to_return.c

@@ -0,0 +1,28 @@
+/*
+ * Copyright © 2025 Valve Corporation
+ * SPDX-License-Identifier: MIT
+ */
+
+#include "nir.h"
+#include "nir_builder.h"
+
+static bool
+pass(nir_builder *b, nir_instr *instr, void *data)
+{
+   if (instr->type != nir_instr_type_jump)
+      return false;
+
+   nir_jump_instr *jump = nir_instr_as_jump(instr);
+   if (jump->type == nir_jump_halt) {
+      jump->type = nir_jump_return;
+      return true;
+   }
+
+   return false;
+}
+
+bool
+nir_lower_halt_to_return(nir_shader *nir)
+{
+   return nir_shader_instructions_pass(nir, pass, nir_metadata_all, NULL);
+}