i965/fs: Recognize nop-MOV instructions early.

And avoid rewriting other instructions unnecessarily. Removes a few
self-moves we weren't able to handle because they were components of a
large VGRF.

instructions in affected programs:     830 -> 826 (-0.48%)

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

1 files changed, 17 insertions, 3 deletions

diff --git a/src/mesa/drivers/dri/i965/brw_fs_register_coalesce.cpp b/src/mesa/drivers/dri/i965/brw_fs_register_coalesce.cpp
index f6d9b680b2..6a8842d07d 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_register_coalesce.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_register_coalesce.cpp
@@ -44,6 +44,16 @@
 #include "brw_fs_live_variables.h"
 
 static bool
+is_nop_mov(const fs_inst *inst)
+{
+   if (inst->opcode == BRW_OPCODE_MOV) {
+      return inst->dst.equals(inst->src[0]);
+   }
+
+   return false;
+}
+
+static bool
 is_coalesce_candidate(const fs_inst *inst, const int *virtual_grf_sizes)
 {
    if (inst->opcode != BRW_OPCODE_MOV ||
@@ -70,9 +80,7 @@ can_coalesce_vars(brw::fs_live_variables *live_intervals,
                   const exec_list *instructions, const fs_inst *inst,
                   int var_to, int var_from)
 {
-   if (live_intervals->vars_interfere(var_from, var_to) &&
-       !inst->dst.equals(inst->src[0])) {
-
+   if (live_intervals->vars_interfere(var_from, var_to)) {
       /* We know that the live ranges of A (var_from) and B (var_to)
        * interfere because of the ->vars_interfere() call above. If the end
        * of B's live range is after the end of A's range, then we know two
@@ -131,6 +139,12 @@ fs_visitor::register_coalesce()
       if (!is_coalesce_candidate(inst, virtual_grf_sizes))
          continue;
 
+      if (is_nop_mov(inst)) {
+         inst->opcode = BRW_OPCODE_NOP;
+         progress = true;
+         continue;
+      }
+
       if (reg_from != inst->src[0].reg) {
          reg_from = inst->src[0].reg;