Mesa (staging/22.0): nir/linker: disable varying from uniform lowering by default

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Module: Mesa
Branch: staging/22.0
Commit: c11e0af8ad390a95751f9ae956d2c2ccb4d22f1c
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=c11e0af8ad390a95751f9ae956d2c2ccb4d22f1c

Author: Qiang Yu <yuq825 at gmail.com>
Date:   Fri Mar 11 13:55:02 2022 +0800

nir/linker: disable varying from uniform lowering by default

This fixes performance regression for Specviewperf/Energy
on AMD GPU. Other GPUs passing varying by memory may choose
to re-enable it as need.

Fixes: 26046250437 ("nir/linker: support uniform when optimizing varying")
Reviewed-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer at amd.com>
Reviewed-by: Marek Olšák <marek.olsak at amd.com>
Signed-off-by: Qiang Yu <yuq825 at gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15341>
(cherry picked from commit 2617e6c028a3823c600b16dbffa5702a68b1cfa7)

Conflicts:
	src/compiler/nir/nir.h

---

 .pick_status.json                      | 2 +-
 src/compiler/nir/nir.h                 | 9 +++++++++
 src/compiler/nir/nir_linking_helpers.c | 3 ++-
 3 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/.pick_status.json b/.pick_status.json
index 23ccaef3886..a6f877c2cc2 100644
--- a/.pick_status.json
+++ b/.pick_status.json
@@ -9604,7 +9604,7 @@
         "description": "nir/linker: disable varying from uniform lowering by default",
         "nominated": true,
         "nomination_type": 1,
-        "resolution": 5,
+        "resolution": 1,
         "because_sha": "260462504372a0b398af8b41bd790a1a557abec9"
     },
     {
diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
index 91660a2f836..272e1d175da 100644
--- a/src/compiler/nir/nir.h
+++ b/src/compiler/nir/nir.h
@@ -3497,6 +3497,15 @@ typedef struct nir_shader_compiler_options {
     * into same slot.
     */
    nir_pack_varying_options pack_varying_options;
+
+   /**
+    * Remove varying loaded from uniform, let fragment shader load the
+    * uniform directly. GPU passing varying by memory can benifit from it
+    * for sure; but GPU passing varying by on chip resource may not.
+    * Because it saves on chip resource but may increase memory pressure when
+    * fragment task is far more than vertex one, so better left it disabled.
+    */
+   bool lower_varying_from_uniform;
 } nir_shader_compiler_options;
 
 typedef struct nir_shader {
diff --git a/src/compiler/nir/nir_linking_helpers.c b/src/compiler/nir/nir_linking_helpers.c
index 872eb205692..69054398a14 100644
--- a/src/compiler/nir/nir_linking_helpers.c
+++ b/src/compiler/nir/nir_linking_helpers.c
@@ -1376,7 +1376,8 @@ nir_link_opt_varyings(nir_shader *producer, nir_shader *consumer)
       nir_ssa_def *ssa = intr->src[1].ssa;
       if (ssa->parent_instr->type == nir_instr_type_load_const) {
          progress |= replace_varying_input_by_constant_load(consumer, intr);
-      } else if (is_direct_uniform_load(ssa, &uni_scalar)) {
+      } else if (consumer->options->lower_varying_from_uniform &&
+                 is_direct_uniform_load(ssa, &uni_scalar)) {
          progress |= replace_varying_input_by_uniform_load(consumer, intr,
                                                            &uni_scalar);
       } else {