vtn: Remove transpose(m0)*m1 fast path

This is broken for games that rely on invariant geometry since the usage
of matrices can affect how gl_Position is computed. The fdot fastpath
relied on if and how fdot is lowered for correctness.

Totals from 6578 (7.73% of 85071) affected shaders:
MaxWaves: 147190 -> 147170 (-0.01%)
Instrs: 4451406 -> 4438140 (-0.30%); split: -0.31%, +0.01%
CodeSize: 23553020 -> 23541772 (-0.05%); split: -0.07%, +0.03%
VGPRs: 302304 -> 302328 (+0.01%)
SpillSGPRs: 1309 -> 1329 (+1.53%)
Latency: 22509985 -> 22177164 (-1.48%); split: -1.48%, +0.00%
InvThroughput: 4862795 -> 4842951 (-0.41%); split: -0.41%, +0.01%
VClause: 85035 -> 84998 (-0.04%); split: -0.06%, +0.02%
SClause: 131008 -> 131055 (+0.04%); split: -0.02%, +0.05%
Copies: 298935 -> 298060 (-0.29%); split: -0.71%, +0.41%
PreSGPRs: 266833 -> 267292 (+0.17%); split: -0.85%, +1.03%
PreVGPRs: 249511 -> 249601 (+0.04%)

Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/9562
cc: mesa-stable

Reviewed-by: Georg Lehmann <dadschoorse@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/26821>
(cherry picked from commit 4d02543853eb86c6c3cb6dd2a84e9a673b44001f)

2 files changed, 10 insertions, 32 deletions

diff --git a/.pick_status.json b/.pick_status.json
index ceaef0e523e..8f04f1575dc 100644
--- a/.pick_status.json
+++ b/.pick_status.json
@@ -544,7 +544,7 @@
         "description": "vtn: Remove transpose(m0)*m1 fast path",
         "nominated": true,
         "nomination_type": 0,
-        "resolution": 0,
+        "resolution": 1,
         "main_sha": null,
         "because_sha": null,
         "notes": null
diff --git a/src/compiler/spirv/vtn_alu.c b/src/compiler/spirv/vtn_alu.c
index 04d71ae6eb2..a6b327f6a02 100644
--- a/src/compiler/spirv/vtn_alu.c
+++ b/src/compiler/spirv/vtn_alu.c
@@ -94,38 +94,16 @@ matrix_multiply(struct vtn_builder *b,
       transpose_result = true;
    }
 
-   if (src0_transpose && !src1_transpose &&
-       glsl_get_base_type(src0->type) == GLSL_TYPE_FLOAT) {
-      /* We already have the rows of src0 and the columns of src1 available,
-       * so we can just take the dot product of each row with each column to
-       * get the result.
-       */
-
-      for (unsigned i = 0; i < src1_columns; i++) {
-         nir_def *vec_src[4];
-         for (unsigned j = 0; j < src0_rows; j++) {
-            vec_src[j] = nir_fdot(&b->nb, src0_transpose->elems[j]->def,
-                                          src1->elems[i]->def);
-         }
-         dest->elems[i]->def = nir_vec(&b->nb, vec_src, src0_rows);
-      }
-   } else {
-      /* We don't handle the case where src1 is transposed but not src0, since
-       * the general case only uses individual components of src1 so the
-       * optimizer should chew through the transpose we emitted for src1.
-       */
-
-      for (unsigned i = 0; i < src1_columns; i++) {
-         /* dest[i] = sum(src0[j] * src1[i][j] for all j) */
+   for (unsigned i = 0; i < src1_columns; i++) {
+      /* dest[i] = sum(src0[j] * src1[i][j] for all j) */
+      dest->elems[i]->def =
+         nir_fmul(&b->nb, src0->elems[src0_columns - 1]->def,
+                  nir_channel(&b->nb, src1->elems[i]->def, src0_columns - 1));
+      for (int j = src0_columns - 2; j >= 0; j--) {
          dest->elems[i]->def =
-            nir_fmul(&b->nb, src0->elems[src0_columns - 1]->def,
-                     nir_channel(&b->nb, src1->elems[i]->def, src0_columns - 1));
-         for (int j = src0_columns - 2; j >= 0; j--) {
-            dest->elems[i]->def =
-               nir_ffma(&b->nb, src0->elems[j]->def,
-                                nir_channel(&b->nb, src1->elems[i]->def, j),
-                                dest->elems[i]->def);
-         }
+            nir_ffma(&b->nb, src0->elems[j]->def,
+                             nir_channel(&b->nb, src1->elems[i]->def, j),
+                             dest->elems[i]->def);
       }
    }