broadcom/compiler: Eliminate redundant setnnmode instructions

This new VIR optimization pass tracks the current NN signedness
mode per block and removes duplicate setnnmode instructions.

When consecutive dot products use the same signedness mode, the backend
emits one setnnmode per dot product. This pass removes the redundant
ones, keeping only the first.

Assisted-by: Claude Opus 4.6
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/41255>

src/broadcom/compiler/meson.build

@@ -11,6 +11,7 @@ libbroadcom_compiler_files = files(
   'vir_opt_copy_propagate.c',
   'vir_opt_dead_code.c',
   'vir_opt_redundant_flags.c',
+  'vir_opt_redundant_setnnmode.c',
   'vir_opt_small_immediates.c',
   'vir_register_allocate.c',
   'vir_to_qpu.c',

src/broadcom/compiler/v3d_compiler.h

@@ -1222,6 +1222,7 @@ bool vir_opt_small_immediates(struct v3d_compile *c);
 bool vir_opt_vpm(struct v3d_compile *c);
 bool vir_opt_constant_alu(struct v3d_compile *c);
 bool vir_opt_alu(struct v3d_compile *c);
+bool vir_opt_redundant_setnnmode(struct v3d_compile *c);
 bool v3d_nir_lower_io(nir_shader *s, struct v3d_compile *c);
 bool v3d_nir_lower_line_smooth(nir_shader *shader);
 bool v3d_nir_lower_logic_ops(nir_shader *s, struct v3d_compile *c);

src/broadcom/compiler/vir.c

@@ -2539,6 +2539,7 @@ vir_optimize(struct v3d_compile *c)
                 OPTPASS(vir_opt_small_immediates);
                 OPTPASS(vir_opt_constant_alu);
                 OPTPASS(vir_opt_alu);
+                OPTPASS(vir_opt_redundant_setnnmode);
 
                 if (!progress)
                         break;

src/broadcom/compiler/vir_opt_redundant_setnnmode.c

@@ -0,0 +1,86 @@
+/*
+ * Copyright © 2026 Raspberry Pi Ltd
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+/**
+ * @file vir_opt_redundant_setnnmode.c
+ *
+ * Eliminates redundant setnnmode instructions within basic blocks.
+ *
+ * When multiple dot products use the same signedness mode, the compiler emits
+ * one setnnmode per dot product. This pass tracks the current NN mode per
+ * basic block and removes duplicates.
+ */
+
+#include "v3d_compiler.h"
+
+static bool
+is_setnnmode_op(enum v3d_qpu_add_op op)
+{
+        switch (op) {
+        case V3D_QPU_A_SETNNMODE_UU:
+        case V3D_QPU_A_SETNNMODE_SU:
+        case V3D_QPU_A_SETNNMODE_US:
+        case V3D_QPU_A_SETNNMODE_SS:
+                return true;
+        default:
+                return false;
+        }
+}
+
+static bool
+vir_opt_redundant_setnnmode_block(struct v3d_compile *c, struct qblock *block)
+{
+        bool progress = false;
+        enum v3d_qpu_add_op current_mode = V3D_QPU_A_NOP;
+        c->cur_block = block;
+        vir_for_each_inst_safe(inst, block) {
+                if (inst->qpu.type != V3D_QPU_INSTR_TYPE_ALU)
+                        continue;
+
+                enum v3d_qpu_add_op op = inst->qpu.alu.add.op;
+
+                if (!is_setnnmode_op(op))
+                        continue;
+
+                if (op == current_mode) {
+                        vir_remove_instruction(c, inst);
+                        progress = true;
+                } else {
+                        current_mode = op;
+                }
+        }
+
+        return progress;
+}
+
+bool
+vir_opt_redundant_setnnmode(struct v3d_compile *c)
+{
+        bool progress = false;
+
+        vir_for_each_block(block, c) {
+                progress = vir_opt_redundant_setnnmode_block(c, block) || progress;
+        }
+
+        return progress;
+}