i965/vec4: Use only one register to spill

The spilling code uses a temporary register for the scratch message. There is no
reason to allocate this register multiple times, and in cases where there are a
lot of scratch reads and writes, doing so is detrimental (running out of
spillable registers).

Signed-off-by: Ben Widawsky <ben@bwidawsk.net>

1 files changed, 13 insertions, 1 deletions

diff --git a/src/mesa/drivers/dri/i965/brw_vec4_reg_allocate.cpp b/src/mesa/drivers/dri/i965/brw_vec4_reg_allocate.cpp
index 5368a75bc0..913a874b75 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4_reg_allocate.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4_reg_allocate.cpp
@@ -342,12 +342,24 @@ vec4_visitor::spill_reg(int spill_reg_nr)
    assert(alloc.sizes[spill_reg_nr] == 1);
    unsigned int spill_offset = c->last_scratch++;
 
+   static struct {
+      int vgrf;
+      float size;
+   } scratch_reg = { -1, 0.0 };
+
    /* Generate spill/unspill instructions for the objects being spilled. */
    foreach_block_and_inst(block, vec4_instruction, inst, cfg) {
       for (unsigned int i = 0; i < 3; i++) {
          if (inst->src[i].file == GRF && inst->src[i].reg == spill_reg_nr) {
+            if (scratch_reg.size < alloc.sizes[spill_reg_nr]) {
+               scratch_reg.vgrf = alloc.allocate(1);
+               scratch_reg.size = alloc.sizes[spill_reg_nr];
+            }
+
+            assert(scratch_reg.vgrf > 0);
+
             src_reg spill_reg = inst->src[i];
-            inst->src[i].reg = alloc.allocate(1);
+            inst->src[i].reg = scratch_reg.vgrf;
             dst_reg temp = dst_reg(inst->src[i]);
 
             emit_scratch_read(block, inst, temp, spill_reg, spill_offset);