[Mesa-dev] [PATCH v3 02/13] mesa/st: glsl_to_tgsi: Split arrays who's elements are only accessed directly

[Gert Wollny]

Array who's elements are only accessed directly are replaced by the
according number of temporary registers. By doing so the otherwise
reserved register range becomes subject to further optimizations like
copy propagation and register merging.

Thanks to the resulting reduced register pressure this patch makes
the piglits

  spec/glsl-1.50/execution -
      variable-indexing/vs-output-array-vec3-index-wr-before-gs
      geometry/max-input-components

pass on r600 (barts) where they would fail before with a "GPR limit exceeded"
error.

v3: * enable this optimization only if the driver requests register merge

v2: * rename method dissolve_arrays to split_arrays
    * unify the tracking and remapping methods for src and st registers
    * also track access to arrays via reladdr*

Signed-off-by: Gert Wollny <gw.fossdev at gmail.com>
---
 src/mesa/state_tracker/st_glsl_to_tgsi.cpp | 117 ++++++++++++++++++++++++++++-
 1 file changed, 116 insertions(+), 1 deletion(-)

diff --git a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
index 1614367a01..e778807b7c 100644
--- a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
+++ b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
@@ -369,6 +369,7 @@ public:
    void copy_propagate(void);
    int eliminate_dead_code(void);
 
+   void split_arrays(void);
    void merge_two_dsts(void);
    void merge_registers(void);
    void renumber_registers(void);
@@ -5400,6 +5401,110 @@ glsl_to_tgsi_visitor::merge_two_dsts(void)
    }
 }
 
+
+
+/* One-dimensional arrays who's elements are only accessed directly are
+ * replaced by an according set of temporary registers that then can become
+ * subject to further optimization steps like copy propagation and
+ * register merging.
+ */
+
+template <typename st_reg>
+void test_indirect_access(const st_reg& reg, bool *has_indirect_access)
+{
+   if (reg.file == PROGRAM_ARRAY) {
+      if (reg.reladdr || reg.reladdr2 || reg.has_index2) {
+         has_indirect_access[reg.array_id] = true;
+         if (reg.reladdr)
+            test_indirect_access(*reg.reladdr, has_indirect_access);
+         if (reg.reladdr2)
+            test_indirect_access(*reg.reladdr, has_indirect_access);
+      }
+   }
+}
+
+template <typename st_reg>
+void remap_array(st_reg& reg, const int *array_remap_info,
+                 const bool *has_indirect_access)
+{
+   if (reg.file == PROGRAM_ARRAY) {
+      if (!has_indirect_access[reg.array_id]) {
+         reg.file = PROGRAM_TEMPORARY;
+         reg.index = reg.index + array_remap_info[reg.array_id];
+         reg.array_id = 0;
+      } else {
+         reg.array_id = array_remap_info[reg.array_id];
+      }
+
+      if (reg.reladdr)
+         remap_array(*reg.reladdr, array_remap_info, has_indirect_access);
+
+      if (reg.reladdr2)
+         remap_array(*reg.reladdr2, array_remap_info, has_indirect_access);
+   }
+}
+
+void
+glsl_to_tgsi_visitor::split_arrays(void)
+{
+   if (!next_array)
+      return;
+
+   bool *has_indirect_access = rzalloc_array(mem_ctx, bool, next_array + 1);
+
+   foreach_in_list(glsl_to_tgsi_instruction, inst, &this->instructions) {
+      for (unsigned j = 0; j < num_inst_src_regs(inst); j++)
+         test_indirect_access(inst->src[j], has_indirect_access);
+
+      for (unsigned j = 0; j < inst->tex_offset_num_offset; j++)
+         test_indirect_access(inst->tex_offsets[j], has_indirect_access);
+
+      for (unsigned j = 0; j < num_inst_dst_regs(inst); j++)
+         test_indirect_access(inst->dst[j], has_indirect_access);
+   }
+
+   unsigned array_offset = 0;
+   unsigned n_remaining_arrays = 0;
+
+   /* Double use: For arrays that get disolved this value will contain
+    * the base index of the temporary registers this array is replaced
+    * with. For arrays that remain it contains the new array ID.
+    */
+   int *array_remap_info = rzalloc_array(has_indirect_access, int,
+                                         next_array + 1);
+
+   for (unsigned i = 1; i <= next_array; ++i) {
+      if (!has_indirect_access[i]) {
+         array_remap_info[i] = this->next_temp + array_offset;
+         array_offset += array_sizes[i-1];
+      } else {
+         array_sizes[n_remaining_arrays] = array_sizes[i-1];
+         array_remap_info[i] = ++n_remaining_arrays;
+      }
+   }
+
+   if (next_array !=  n_remaining_arrays) {
+
+      foreach_in_list(glsl_to_tgsi_instruction, inst, &this->instructions) {
+
+         for (unsigned j = 0; j < num_inst_src_regs(inst); j++)
+            remap_array(inst->src[j], array_remap_info, has_indirect_access);
+
+         for (unsigned j = 0; j < inst->tex_offset_num_offset; j++)
+            remap_array(inst->tex_offsets[j], array_remap_info, has_indirect_access);
+
+         for (unsigned j = 0; j < num_inst_dst_regs(inst); j++) {
+            remap_array(inst->dst[j], array_remap_info, has_indirect_access);
+         }
+      }
+   }
+
+   ralloc_free(has_indirect_access);
+
+   this->next_temp += array_offset;
+   next_array = n_remaining_arrays;
+}
+
 /* Merges temporary registers together where possible to reduce the number of
  * registers needed to run a program.
  *
@@ -6892,8 +6997,18 @@ get_mesa_program_tgsi(struct gl_context *ctx,
    while (v->eliminate_dead_code());
 
    v->merge_two_dsts();
-   if (!skip_merge_registers)
+
+   if (!skip_merge_registers) {
+
+      v->split_arrays();
+      v->copy_propagate();
+      while (v->eliminate_dead_code());
+
       v->merge_registers();
+      v->copy_propagate();
+      while (v->eliminate_dead_code());
+   }
+
    v->renumber_registers();
 
    /* Write the END instruction. */
-- 
2.16.1