[PATCH v4 0/1] MR349: vkd3d-shader/ir: Remove dead code during normalisation.

[Giovanni Mascellani (＠giomasce)]

--
  v4: vkd3d-shader/ir: Remove dead code during normalisation.

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

[PATCH v4 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 | 93 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 93 insertions(+)

diff --git a/libs/vkd3d-shader/ir.c b/libs/vkd3d-shader/ir.c
index 6d7c89653..1137f6e4e 100644
--- a/libs/vkd3d-shader/ir.c
+++ b/libs/vkd3d-shader/ir.c
@@ -1260,6 +1260,96 @@ 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;
+
+            /* `depth' is counted with respect to where the dead code
+             * segment began. So it starts at zero and it signals the
+             * termination of the dead code segment when it would
+             * become negative. */
+            case VKD3DSIH_BREAK:
+            case VKD3DSIH_RET:
+            case VKD3DSIH_CONTINUE:
+                if (dead)
+                {
+                    vkd3d_shader_instruction_make_nop(ins);
+                }
+                else
+                {
+                    dead = true;
+                    depth = 0;
+                }
+                break;
+
+            /* If `case' or `default' appears at zero depth, it means
+             * that they are a possible target for the corresponding
+             * switch, so the code is live again. */
+            case VKD3DSIH_CASE:
+            case VKD3DSIH_DEFAULT:
+                if (dead)
+                {
+                    if (depth == 0)
+                        dead = false;
+                    else
+                        vkd3d_shader_instruction_make_nop(ins);
+                }
+                break;
+
+            /* Phase instructions can only appear in hull shaders and
+             * outside of any block. When a phase returns, control is
+             * moved to the following phase, so they make code live
+             * again. */
+            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 +1377,9 @@ 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)]

On Thu Sep 21 14:44:27 2023 +0000, Conor McCarthy wrote:
> 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.

I added a few comments, hopefully they make the logic clearer.

[PATCH v4 0/1] MR349: vkd3d-shader/ir: Remove dead code during normalisation. - approved

[Conor McCarthy (＠cmccarthy)]

This merge request was approved by Conor McCarthy.

[PATCH v4 0/1] MR349: vkd3d-shader/ir: Remove dead code during normalisation. - approved

[Henri Verbeet (＠hverbeet)]

This merge request was approved by Henri Verbeet.