Mesa (master): spirv: repair ssa defs for switchs with only default case

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Module: Mesa
Branch: master
Commit: 4220befb383112798b1afc1ba13419ed79470cba
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=4220befb383112798b1afc1ba13419ed79470cba

Author: Andrii Simiklit <andrii.simiklit at globallogic.com>
Date:   Tue Nov 24 14:28:12 2020 +0200

spirv: repair ssa defs for switchs with only default case

This fixes OpSwitch corner case when switch doesn't have any targets
just a `default` and SSAs defined in it is used after switch block
directly without phis.

v2: Just use `repair_ssa` for all structured control-flow cases
               ( - Jason Ekstrand <jason at jlekstrand.net>
                 - Caio Marcelo de Oliveira Filho <caio.oliveira at intel.com> )

Closes: #3787
Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira at intel.com>
Signed-off-by: Andrii Simiklit <andrii.simiklit at globallogic.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7755>

---

 src/compiler/spirv/vtn_cfg.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/src/compiler/spirv/vtn_cfg.c b/src/compiler/spirv/vtn_cfg.c
index 8d0794ed4af..dd91352bfbd 100644
--- a/src/compiler/spirv/vtn_cfg.c
+++ b/src/compiler/spirv/vtn_cfg.c
@@ -1393,12 +1393,22 @@ vtn_function_emit(struct vtn_builder *b, struct vtn_function *func,
 
    nir_rematerialize_derefs_in_use_blocks_impl(impl);
 
-   /* Continue blocks for loops get inserted before the body of the loop
-    * but instructions in the continue may use SSA defs in the loop body.
-    * Therefore, we need to repair SSA to insert the needed phi nodes.
+   /*
+    * There are some cases where we need to repair SSA to insert
+    * the needed phi nodes:
+    *
+    * - Continue blocks for loops get inserted before the body of the loop
+    *   but instructions in the continue may use SSA defs in the loop body.
+    *
+    * - Early termination instructions `OpKill` and `OpTerminateInvocation`,
+    *   in NIR. They're represented by regular intrinsics with no control-flow
+    *   semantics. This means that the SSA form from the SPIR-V may not
+    *   100% match NIR.
+    *
+    * - Switches with only default case may also define SSA which may
+    *   subsequently be used out of the switch.
     */
-   if (func->nir_func->impl->structured &&
-       (b->has_loop_continue || b->has_early_terminate))
+   if (func->nir_func->impl->structured)
       nir_repair_ssa_impl(impl);
 
    func->emitted = true;