Mesa (main): nir/inline_functions: Handle halting functions.

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Module: Mesa
Branch: main
Commit: aa8179e33f8b1fce5dd0a1df3cc265cc3e3d9cbd
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=aa8179e33f8b1fce5dd0a1df3cc265cc3e3d9cbd

Author: Bas Nieuwenhuizen <bas at basnieuwenhuizen.nl>
Date:   Mon Jul 26 17:05:20 2021 +0200

nir/inline_functions: Handle halting functions.

Without this stitch_blocks complains about ending in a jump with a
non-empty block after the inserted body.

I hit this with CTS raytracing tests where we tried to inline a
function that basically ended up being something like

{
   ignore_ray_intersection
   halt
}

I kept the nop path when possible as that does not leave a mess
for the optimization loop to optimize.

Reviewed-by: Rhys Perry <pendingchaos02 at gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12163>

---

 src/compiler/nir/nir_inline_functions.c | 27 ++++++++++++++++++++-------
 1 file changed, 20 insertions(+), 7 deletions(-)

diff --git a/src/compiler/nir/nir_inline_functions.c b/src/compiler/nir/nir_inline_functions.c
index b1399897be5..eba53d06029 100644
--- a/src/compiler/nir/nir_inline_functions.c
+++ b/src/compiler/nir/nir_inline_functions.c
@@ -26,6 +26,12 @@
 #include "nir_control_flow.h"
 #include "nir_vla.h"
 
+static bool function_ends_in_jump(nir_function_impl *impl)
+{
+   nir_block *last_block = nir_impl_last_block(impl);
+   return nir_block_ends_in_jump(last_block);
+}
+
 void nir_inline_function_impl(struct nir_builder *b,
                               const nir_function_impl *impl,
                               nir_ssa_def **params,
@@ -33,11 +39,6 @@ void nir_inline_function_impl(struct nir_builder *b,
 {
    nir_function_impl *copy = nir_function_impl_clone(b->shader, impl);
 
-   /* Insert a nop at the cursor so we can keep track of where things are as
-    * we add/remove stuff from the CFG.
-    */
-   nir_intrinsic_instr *nop = nir_nop(b);
-
    exec_list_append(&b->impl->locals, &copy->locals);
    exec_list_append(&b->impl->registers, &copy->registers);
 
@@ -104,12 +105,24 @@ void nir_inline_function_impl(struct nir_builder *b,
       }
    }
 
+   bool nest_if = function_ends_in_jump(copy);
+
    /* Pluck the body out of the function and place it here */
    nir_cf_list body;
    nir_cf_list_extract(&body, &copy->body);
-   nir_cf_reinsert(&body, nir_before_instr(&nop->instr));
 
-   b->cursor = nir_instr_remove(&nop->instr);
+   if (nest_if) {
+      nir_if *cf = nir_push_if(b, nir_imm_bool(b, true));
+      nir_cf_reinsert(&body, nir_after_cf_list(&cf->then_list));
+      nir_pop_if(b, cf);
+   } else {
+      /* Insert a nop at the cursor so we can keep track of where things are as
+       * we add/remove stuff from the CFG.
+       */
+      nir_intrinsic_instr *nop = nir_nop(b);
+      nir_cf_reinsert(&body, nir_before_instr(&nop->instr));
+      b->cursor = nir_instr_remove(&nop->instr);
+   }
 }
 
 static bool inline_function_impl(nir_function_impl *impl, struct set *inlined);