Mesa (master): i965/fs: Simplify interference scan in register coalescing.

[Matt Turner]

Module: Mesa
Branch: master
Commit: 5ff1e446d44bb9d50f84883c7058635cb070e069
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=5ff1e446d44bb9d50f84883c7058635cb070e069

Author: Matt Turner <mattst88 at gmail.com>
Date:   Wed Apr  9 14:31:10 2014 -0700

i965/fs: Simplify interference scan in register coalescing.

We were starting at the beginning of the instruction list, rather than
with the MOV instruction itself. This allows us to coalesce after
control flow.

Excluding the shaders from an unreleased title, the shader-db results:

total instructions in shared programs: 1603791 -> 1594215 (-0.60%)
instructions in affected programs:     678772 -> 669196 (-1.41%)
GAINED:                                5
LOST:                                  0

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

---

 .../drivers/dri/i965/brw_fs_register_coalesce.cpp  |   22 ++++++++------------
 1 file changed, 9 insertions(+), 13 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 01b672f..020d992 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_register_coalesce.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_register_coalesce.cpp
@@ -77,7 +77,7 @@ is_coalesce_candidate(const fs_inst *inst, const int *virtual_grf_sizes)
 
 static bool
 can_coalesce_vars(brw::fs_live_variables *live_intervals,
-                  const exec_list *instructions, const fs_inst *inst,
+                  const exec_list *instructions, const fs_inst *inst, int ip,
                   int var_to, int var_from)
 {
    if (!live_intervals->vars_interfere(var_from, var_to))
@@ -96,21 +96,15 @@ can_coalesce_vars(brw::fs_live_variables *live_intervals,
    if (live_intervals->end[var_to] > live_intervals->end[var_from])
       return false;
 
-   int scan_ip = -1;
-
-   foreach_list(n, instructions) {
-      fs_inst *scan_inst = (fs_inst *)n;
-      scan_ip++;
+   assert(ip >= live_intervals->start[var_to]);
 
+   fs_inst *scan_inst;
+   for (scan_inst = (fs_inst *)inst->next;
+        !scan_inst->is_tail_sentinel() && ip <= live_intervals->end[var_to];
+        scan_inst = (fs_inst *)scan_inst->next, ip++) {
       if (scan_inst->is_control_flow())
          return false;
 
-      if (scan_ip <= live_intervals->start[var_to])
-         continue;
-
-      if (scan_ip > live_intervals->end[var_to])
-         break;
-
       if (scan_inst->dst.equals(inst->dst) ||
           scan_inst->dst.equals(inst->src[0]))
          return false;
@@ -133,9 +127,11 @@ fs_visitor::register_coalesce()
    fs_inst *mov[MAX_SAMPLER_MESSAGE_SIZE];
    int var_to[MAX_SAMPLER_MESSAGE_SIZE];
    int var_from[MAX_SAMPLER_MESSAGE_SIZE];
+   int ip = -1;
 
    foreach_list(node, &this->instructions) {
       fs_inst *inst = (fs_inst *)node;
+      ip++;
 
       if (!is_coalesce_candidate(inst, virtual_grf_sizes))
          continue;
@@ -174,7 +170,7 @@ fs_visitor::register_coalesce()
          var_to[i] = live_intervals->var_from_vgrf[reg_to] + reg_to_offset[i];
          var_from[i] = live_intervals->var_from_vgrf[reg_from] + i;
 
-         if (!can_coalesce_vars(live_intervals, &instructions, inst,
+         if (!can_coalesce_vars(live_intervals, &instructions, inst, ip,
                                 var_to[i], var_from[i])) {
             can_coalesce = false;
             reg_from = -1;