[PATCH v3 0/1] MR349: vkd3d-shader/ir: Remove dead code during normalisation.

[Giovanni Mascellani (＠giomasce)]

--
  v3: vkd3d-shader/ir: Remove dead code during normalisation.

https://gitlab.winehq.org/wine/vkd3d/-/merge_requests/349

[PATCH v3 1/1] vkd3d-shader/ir: Remove dead code during normalisation.

[Giovanni Mascellani]

From: Giovanni Mascellani

The SPIR-V backend generates invalid SPIR-V code when
VSIR has dead code (except for NOPs).
---
 libs/vkd3d-shader/ir.c | 82 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 82 insertions(+)

diff --git a/libs/vkd3d-shader/ir.c b/libs/vkd3d-shader/ir.c
index 6d7c89653..ffb1ff716 100644
--- a/libs/vkd3d-shader/ir.c
+++ b/libs/vkd3d-shader/ir.c
@@ -1260,6 +1260,85 @@ static enum vkd3d_result instruction_array_normalise_flat_constants(struct vkd3d
     return VKD3D_OK;
 }

+static void remove_dead_code(struct vkd3d_shader_parser *parser)
+{
+    size_t i, depth = 0;
+    bool dead = false;
+
+    for (i = 0; i < parser->instructions.count; ++i)
+    {
+        struct vkd3d_shader_instruction *ins = &parser->instructions.elements[i];
+
+        switch (ins->handler_idx)
+        {
+            case VKD3DSIH_IF:
+            case VKD3DSIH_LOOP:
+            case VKD3DSIH_SWITCH:
+                if (dead)
+                {
+                    vkd3d_shader_instruction_make_nop(ins);
+                    ++depth;
+                }
+                break;
+
+            case VKD3DSIH_ENDIF:
+            case VKD3DSIH_ENDLOOP:
+            case VKD3DSIH_ENDSWITCH:
+            case VKD3DSIH_ELSE:
+                if (dead)
+                {
+                    if (depth > 0)
+                    {
+                        vkd3d_shader_instruction_make_nop(ins);
+                        if (ins->handler_idx != VKD3DSIH_ELSE)
+                            --depth;
+                    }
+                    else
+                    {
+                        dead = false;
+                    }
+                }
+                break;
+
+            case VKD3DSIH_BREAK:
+            case VKD3DSIH_RET:
+            case VKD3DSIH_CONTINUE:
+                if (dead)
+                {
+                    vkd3d_shader_instruction_make_nop(ins);
+                }
+                else
+                {
+                    dead = true;
+                    depth = 0;
+                }
+                break;
+
+            case VKD3DSIH_CASE:
+            case VKD3DSIH_DEFAULT:
+                if (dead)
+                {
+                    if (depth == 0)
+                        dead = false;
+                    else
+                        vkd3d_shader_instruction_make_nop(ins);
+                }
+                break;
+
+            case VKD3DSIH_HS_CONTROL_POINT_PHASE:
+            case VKD3DSIH_HS_FORK_PHASE:
+            case VKD3DSIH_HS_JOIN_PHASE:
+                dead = false;
+                break;
+
+            default:
+                if (dead)
+                    vkd3d_shader_instruction_make_nop(ins);
+                break;
+        }
+    }
+}
+
 enum vkd3d_result vkd3d_shader_normalise(struct vkd3d_shader_parser *parser,
         const struct vkd3d_shader_compile_info *compile_info)
 {
@@ -1287,6 +1366,9 @@ enum vkd3d_result vkd3d_shader_normalise(struct vkd3d_shader_parser *parser,
     if (result >= 0)
         result = instruction_array_normalise_flat_constants(parser);

+    if (result >= 0)
+        remove_dead_code(parser);
+
     if (result >= 0 && TRACE_ON())
         vkd3d_shader_trace(instructions, &parser->shader_version);

[Giovanni Mascellani (＠giomasce)]

I fixed some cases not being handled properly (or at all). Now tests should pass. So they do locally, at least.

[Conor McCarthy (＠cmccarthy)]

In `spirv_compiler_emit_control_flow_instruction()`, `break` and `continue` set the depth not to zero but to the innermost breakable construct. Setting `depth` to zero in this patch seems to work, but a comment explaining exactly why would be helpful.