[Mesa-dev] [PATCH 2/2] intel/fs: Take into account amount of data read in spilling cost heuristic.

[Francisco Jerez]

Until now the spilling cost calculation was neglecting the amount of
data read from the register during the spilling cost calculation.
This caused it to make suboptimal decisions in some cases leading to
higher memory bandwidth usage than necessary.

Improves Unigine Heaven performance by ~4% on BDW, reversing an
unintended FPS regression from my previous commit
147e71242ce539ff28e282f009c332818c35f5ac with n=12 and statistical
significance 5%.  In addition SynMark2 OglCSDof performance is
improved by an additional ~5% on SKL, and a Kerbal Space Program
apitrace around the Moho planet I can provide on request improves by
~20%.

Cc: <mesa-stable at lists.freedesktop.org>
---
 src/intel/compiler/brw_fs_reg_allocate.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/intel/compiler/brw_fs_reg_allocate.cpp b/src/intel/compiler/brw_fs_reg_allocate.cpp
index 2d4d46e..ec8e116 100644
--- a/src/intel/compiler/brw_fs_reg_allocate.cpp
+++ b/src/intel/compiler/brw_fs_reg_allocate.cpp
@@ -822,7 +822,7 @@ fs_visitor::choose_spill_reg(struct ra_graph *g)
    foreach_block_and_inst(block, fs_inst, inst, cfg) {
       for (unsigned int i = 0; i < inst->sources; i++) {
 	 if (inst->src[i].file == VGRF)
-            spill_costs[inst->src[i].nr] += block_scale;
+            spill_costs[inst->src[i].nr] += regs_read(inst, i) * block_scale;
       }
 
       if (inst->dst.file == VGRF)
-- 
2.10.2