lima/ppir: handle write to dead registers in ppir

nir can output writes to dead registers when expanding vec4 operations
to non-ssa registers. In that case, some components of the vec4 may be
assigned but never read. These are also not currently removed by a nir
dead code elimination pass as they are not ssa.
In order to prevent regalloc from allocating a live register for this
operation, an interference must be assigned to it during liveness
analysis.

This workaround may be removed in the future if the assignments to dead
components can be removed earlier in ppir or nir.

Signed-off-by: Erico Nunes <nunes.erico@gmail.com>
Reviewed-by: Vasily Khoruzhick <anarsoul@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3502>

diff --git a/.gitlab-ci/deqp-lima-fails.txt b/.gitlab-ci/deqp-lima-fails.txt
index 3f88017..c298e8b 100644 (file)
--- a/.gitlab-ci/deqp-lima-fails.txt
+++ b/.gitlab-ci/deqp-lima-fails.txt
@@ -184,7 +184,6 @@ dEQP-GLES2.functional.shaders.random.exponential.fragment.37
 dEQP-GLES2.functional.shaders.random.exponential.fragment.5
 dEQP-GLES2.functional.shaders.random.exponential.fragment.74
 dEQP-GLES2.functional.shaders.random.texture.fragment.28
-dEQP-GLES2.functional.shaders.random.texture.fragment.106
 dEQP-GLES2.functional.shaders.random.trigonometric.fragment.1
 dEQP-GLES2.functional.shaders.random.trigonometric.fragment.65
 dEQP-GLES2.functional.shaders.random.trigonometric.fragment.69

diff --git a/src/gallium/drivers/lima/ir/pp/liveness.c b/src/gallium/drivers/lima/ir/pp/liveness.c
index 2684025..1bc1dc8 100644 (file)
--- a/src/gallium/drivers/lima/ir/pp/liveness.c
+++ b/src/gallium/drivers/lima/ir/pp/liveness.c
@@ -194,9 +194,17 @@ ppir_liveness_instr_dest(ppir_compiler *comp, ppir_instr *instr)
 
       struct set_entry *live = _mesa_set_search(instr->live_in_set,
                                                 &instr->live_in[reg->regalloc_index]);
+
+      /* If a register is written but wasn't read in a later instruction, it is
+       * either dead code or a bug. For now, assign an interference to it to
+       * ensure it doesn't get assigned a live register and overwrites it. */
+      if (!live) {
+         instr->live_out[reg->regalloc_index].reg = reg;
+         _mesa_set_add(instr->live_out_set, &instr->live_out[reg->regalloc_index]);
+         continue;
+      }
+
       if (dest->type == ppir_target_ssa) {
-         if (!live)
-            continue;
          /* reg is written and ssa, is not live before instr */
          _mesa_set_remove_key(instr->live_in_set, &instr->live_in[reg->regalloc_index]);
       }
@@ -204,9 +212,8 @@ ppir_liveness_instr_dest(ppir_compiler *comp, ppir_instr *instr)
          unsigned int mask = ppir_src_get_mask(node);
          /* written reg is type register, need to check if this clears
           * the remaining mask to remove it from the live set */
-         if (!live ||
-               instr->live_in[reg->regalloc_index].mask ==
-               (instr->live_in[reg->regalloc_index].mask & ~mask))
+         if (instr->live_in[reg->regalloc_index].mask ==
+             (instr->live_in[reg->regalloc_index].mask & ~mask))
             continue;
 
          instr->live_in[reg->regalloc_index].mask &= ~mask;