broadcom/compiler: allow ldunifa with read-only SSBOs

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14830>

src/broadcom/compiler/nir_to_vir.c

@@ -3003,8 +3003,11 @@ emit_ldunifa(struct v3d_compile *c, struct qreg *result)
 }
 
 static bool
-ntq_emit_load_ubo_unifa(struct v3d_compile *c, nir_intrinsic_instr *instr)
+ntq_emit_load_unifa(struct v3d_compile *c, nir_intrinsic_instr *instr)
 {
+        assert(instr->intrinsic == nir_intrinsic_load_ubo ||
+               instr->intrinsic == nir_intrinsic_load_ssbo);
+
         /* Every ldunifa auto-increments the unifa address by 4 bytes, so our
          * current unifa offset is 4 bytes ahead of the offset of the last load.
          */
@@ -3015,6 +3018,11 @@ ntq_emit_load_ubo_unifa(struct v3d_compile *c, nir_intrinsic_instr *instr)
         if (nir_src_is_divergent(instr->src[1]))
                 return false;
 
+        /* We can only use unifa with SSBOs if they are read-only */
+        bool is_ubo = instr->intrinsic == nir_intrinsic_load_ubo;
+        if (!is_ubo && !(nir_intrinsic_access(instr) & ACCESS_NON_WRITEABLE))
+                return false;
+
         /* ldunifa is a 32-bit load instruction so we can only use it with
          * 32-bit aligned addresses. We always produce 32-bit aligned addresses
          * except for types smaller than 32-bit, so in these cases we can only
@@ -3046,11 +3054,11 @@ ntq_emit_load_ubo_unifa(struct v3d_compile *c, nir_intrinsic_instr *instr)
          * shifted up by 1 (0 is gallium's constant buffer 0).
          */
         uint32_t index = nir_src_as_uint(instr->src[0]);
-        if (c->key->environment == V3D_ENVIRONMENT_OPENGL)
+        if (is_ubo && c->key->environment == V3D_ENVIRONMENT_OPENGL)
                 index++;
 
         /* We can only keep track of the last unifa address we used with
-         * constant offset loads. If the new load targets the same UBO and
+         * constant offset loads. If the new load targets the same buffer and
          * is close enough to the previous load, we can skip the unifa register
          * write by emitting dummy ldunifa instructions to update the unifa
          * address.
@@ -3060,6 +3068,7 @@ ntq_emit_load_ubo_unifa(struct v3d_compile *c, nir_intrinsic_instr *instr)
         if (dynamic_src) {
                 c->current_unifa_block = NULL;
         } else if (c->cur_block == c->current_unifa_block &&
+                   c->current_unifa_is_ubo == is_ubo &&
                    c->current_unifa_index == index &&
                    c->current_unifa_offset <= const_offset &&
                    c->current_unifa_offset + max_unifa_skip_dist >= const_offset) {
@@ -3067,18 +3076,25 @@ ntq_emit_load_ubo_unifa(struct v3d_compile *c, nir_intrinsic_instr *instr)
                 ldunifa_skips = (const_offset - c->current_unifa_offset) / 4;
         } else {
                 c->current_unifa_block = c->cur_block;
+                c->current_unifa_is_ubo = is_ubo;
                 c->current_unifa_index = index;
                 c->current_unifa_offset = const_offset;
         }
 
         if (!skip_unifa) {
-                struct qreg base_offset =
+                struct qreg base_offset = is_ubo ?
                         vir_uniform(c, QUNIFORM_UBO_ADDR,
-                                    v3d_unit_data_create(index, const_offset));
+                                    v3d_unit_data_create(index, const_offset)) :
+                        vir_uniform(c, QUNIFORM_SSBO_OFFSET, index);
 
                 struct qreg unifa = vir_reg(QFILE_MAGIC, V3D_QPU_WADDR_UNIFA);
                 if (!dynamic_src) {
-                        vir_MOV_dest(c, unifa, base_offset);
+                        if (is_ubo) {
+                                vir_MOV_dest(c, unifa, base_offset);
+                        } else {
+                                vir_ADD_dest(c, unifa, base_offset,
+                                             vir_uniform_ui(c, const_offset));
+                        }
                 } else {
                         vir_ADD_dest(c, unifa, base_offset,
                                      ntq_get_src(c, instr->src[1], 0));
@@ -3185,7 +3201,8 @@ ntq_emit_intrinsic(struct v3d_compile *c, nir_intrinsic_instr *instr)
                 break;
 
         case nir_intrinsic_load_ubo:
-                if (!ntq_emit_load_ubo_unifa(c, instr))
+        case nir_intrinsic_load_ssbo:
+                if (!ntq_emit_load_unifa(c, instr))
                         ntq_emit_tmu_general(c, instr, false);
                 break;
 
@@ -3199,7 +3216,6 @@ ntq_emit_intrinsic(struct v3d_compile *c, nir_intrinsic_instr *instr)
         case nir_intrinsic_ssbo_atomic_xor:
         case nir_intrinsic_ssbo_atomic_exchange:
         case nir_intrinsic_ssbo_atomic_comp_swap:
-        case nir_intrinsic_load_ssbo:
         case nir_intrinsic_store_ssbo:
                 ntq_emit_tmu_general(c, instr, false);
                 break;

src/broadcom/compiler/v3d_compiler.h

@@ -720,6 +720,7 @@ struct v3d_compile {
         struct qblock *current_unifa_block;
         int32_t current_unifa_index;
         uint32_t current_unifa_offset;
+        bool current_unifa_is_ubo;
 
         /* State for whether we're executing on each channel currently.  0 if
          * yes, otherwise a block number + 1 that the channel jumped to.