From 24d35a56d99ccc9ff23d4aa058f857652fbc31f2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Pavel=20Ondra=C4=8Dka?= <pavel.ondracka@gmail.com>
Date: Mon, 17 Jul 2023 13:17:04 +0200
Subject: [PATCH] r300: reorder for easier presubtract 1-x pattern recognition

It is much easier to just add a simple late algebraic pass than actually
trying to teach the backend to recognize all the different patterns.

RV530 shader-db:
total instructions in shared programs: 129643 -> 129468 (-0.13%)
instructions in affected programs: 17665 -> 17490 (-0.99%)
helped: 176
HURT: 39
total presub in shared programs: 4912 -> 5411 (10.16%)
presub in affected programs: 1651 -> 2150 (30.22%)
helped: 0
HURT: 287
total temps in shared programs: 16904 -> 16918 (0.08%)
temps in affected programs: 812 -> 826 (1.72%)
helped: 25
HURT: 37
total cycles in shared programs: 194771 -> 194675 (-0.05%)
cycles in affected programs: 28096 -> 28000 (-0.34%)
helped: 146
HURT: 41

Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/9364
Reviewed-by: Filip Gawin <filip.gawin@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24830>
---
 src/gallium/drivers/r300/compiler/nir_to_rc.c |  6 +++++
 src/gallium/drivers/r300/compiler/r300_nir.h  |  4 ++++
 .../r300/compiler/r300_nir_algebraic.py       | 22 +++++++++++++++++++
 3 files changed, 32 insertions(+)

diff --git a/src/gallium/drivers/r300/compiler/nir_to_rc.c b/src/gallium/drivers/r300/compiler/nir_to_rc.c
index 988f13da416..7a783a1cefb 100644
--- a/src/gallium/drivers/r300/compiler/nir_to_rc.c
+++ b/src/gallium/drivers/r300/compiler/nir_to_rc.c
@@ -26,6 +26,7 @@
 #include "compiler/nir/nir_legacy.h"
 #include "compiler/nir/nir_worklist.h"
 #include "nir_to_rc.h"
+#include "r300_nir.h"
 #include "pipe/p_screen.h"
 #include "pipe/p_state.h"
 #include "tgsi/tgsi_dump.h"
@@ -2433,6 +2434,11 @@ const void *nir_to_rc_options(struct nir_shader *s,
       }
    } while (progress);
 
+   if (s->info.stage == MESA_SHADER_FRAGMENT) {
+      NIR_PASS_V(s, r300_nir_prepare_presubtract);
+      NIR_PASS_V(s, r300_nir_clean_double_fneg);
+   }
+
    NIR_PASS_V(s, nir_lower_int_to_float);
    NIR_PASS_V(s, nir_lower_bool_to_float,
               !options->lower_cmp && !options->lower_fabs);
diff --git a/src/gallium/drivers/r300/compiler/r300_nir.h b/src/gallium/drivers/r300/compiler/r300_nir.h
index 111bf84e8d0..951e0a8cdbd 100644
--- a/src/gallium/drivers/r300/compiler/r300_nir.h
+++ b/src/gallium/drivers/r300/compiler/r300_nir.h
@@ -36,4 +36,8 @@ extern bool r300_nir_fuse_fround_d3d9(struct nir_shader *shader);
 
 extern bool r300_nir_lower_bool_to_float(struct nir_shader *shader);
 
+extern bool r300_nir_prepare_presubtract(struct nir_shader *shader);
+
+extern bool r300_nir_clean_double_fneg(struct nir_shader *shader);
+
 #endif /* R300_NIR_H */
diff --git a/src/gallium/drivers/r300/compiler/r300_nir_algebraic.py b/src/gallium/drivers/r300/compiler/r300_nir_algebraic.py
index c4ce7d22722..7967f14f4f2 100644
--- a/src/gallium/drivers/r300/compiler/r300_nir_algebraic.py
+++ b/src/gallium/drivers/r300/compiler/r300_nir_algebraic.py
@@ -63,6 +63,22 @@ r300_nir_fuse_fround_d3d9 = [
          ('fround_even', 'a'))
 ]
 
+# Here are some specific optimizations for code reordering such that the backend
+# has easier task of recognizing output modifiers and presubtract patterns.
+r300_nir_prepare_presubtract = [
+        # Backend can only recognize 1 - x pattern.
+        (('fadd', ('fneg', a), 1.0), ('fadd', 1.0, ('fneg', a))),
+        (('fadd', a, -1.0), ('fneg', ('fadd', 1.0, ('fneg', a)))),
+        (('fadd', -1.0, a), ('fneg', ('fadd', 1.0, ('fneg', a)))),
+]
+
+# Previous prepare_presubtract pass can sometimes produce double fneg patterns.
+# The backend copy propagate could handle it, but the nir to tgsi translation
+# does not and blows up. Just run a simple pass to clean it up.
+r300_nir_clean_double_fneg = [
+        (('fneg', ('fneg', a)), a)
+]
+
 def main():
     parser = argparse.ArgumentParser()
     parser.add_argument('-p', '--import-path', required=True)
@@ -103,5 +119,11 @@ def main():
         f.write(nir_algebraic.AlgebraicPass("r300_nir_lower_bool_to_float",
                                             r300_nir_lower_bool_to_float).render())
 
+        f.write(nir_algebraic.AlgebraicPass("r300_nir_prepare_presubtract",
+                                            r300_nir_prepare_presubtract).render())
+
+        f.write(nir_algebraic.AlgebraicPass("r300_nir_clean_double_fneg",
+                                            r300_nir_clean_double_fneg).render())
+
 if __name__ == '__main__':
     main()