i965/vs: Implement register spilling.

To validate this code, I ran piglit -t vs quick.tests with the "go spill
everything" debugging code enabled.  There was only one regression:
glsl-vs-unroll-explosion simply ran out of registers.  This should be
fine in the real world, since no one actually spills every single
register.

NOTE: This is a candidate for the 9.0 branch. Even if it proves to have
bugs, it's likely better than simply failing to compile.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>

1 files changed, 127 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 2cda678..01ca6b5 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4_reg_allocate.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4_reg_allocate.cpp
@@ -203,8 +203,16 @@ vec4_visitor::reg_allocate()
    }
 
    if (!ra_allocate_no_spills(g)) {
+      /* Failed to allocate registers.  Spill a reg, and the caller will
+       * loop back into here to try again.
+       */
+      int reg = choose_spill_reg(g);
+      if (reg == -1) {
+         fail("no register to spill\n");
+      } else {
+         spill_reg(reg);
+      }
       ralloc_free(g);
-      fail("No register spilling support yet\n");
       return;
    }
 
@@ -233,4 +241,122 @@ vec4_visitor::reg_allocate()
    ralloc_free(g);
 }
 
+void
+vec4_visitor::evaluate_spill_costs(float *spill_costs, bool *no_spill)
+{
+   float loop_scale = 1.0;
+
+   for (int i = 0; i < this->virtual_grf_count; i++) {
+      spill_costs[i] = 0.0;
+      no_spill[i] = virtual_grf_sizes[i] != 1;
+   }
+
+   /* Calculate costs for spilling nodes.  Call it a cost of 1 per
+    * spill/unspill we'll have to do, and guess that the insides of
+    * loops run 10 times.
+    */
+   foreach_list(node, &this->instructions) {
+      vec4_instruction *inst = (vec4_instruction *) node;
+
+      for (unsigned int i = 0; i < 3; i++) {
+	 if (inst->src[i].file == GRF) {
+	    spill_costs[inst->src[i].reg] += loop_scale;
+            if (inst->src[i].reladdr)
+               no_spill[inst->src[i].reg] = true;
+	 }
+      }
+
+      if (inst->dst.file == GRF) {
+	 spill_costs[inst->dst.reg] += loop_scale;
+         if (inst->dst.reladdr)
+            no_spill[inst->dst.reg] = true;
+      }
+
+      switch (inst->opcode) {
+
+      case BRW_OPCODE_DO:
+	 loop_scale *= 10;
+	 break;
+
+      case BRW_OPCODE_WHILE:
+	 loop_scale /= 10;
+	 break;
+
+      case VS_OPCODE_SCRATCH_READ:
+      case VS_OPCODE_SCRATCH_WRITE:
+         for (int i = 0; i < 3; i++) {
+            if (inst->src[i].file == GRF)
+               no_spill[inst->src[i].reg] = true;
+         }
+	 if (inst->dst.file == GRF)
+	    no_spill[inst->dst.reg] = true;
+	 break;
+
+      default:
+	 break;
+      }
+   }
+}
+
+int
+vec4_visitor::choose_spill_reg(struct ra_graph *g)
+{
+   float spill_costs[this->virtual_grf_count];
+   bool no_spill[this->virtual_grf_count];
+
+   evaluate_spill_costs(spill_costs, no_spill);
+
+   for (int i = 0; i < this->virtual_grf_count; i++) {
+      if (!no_spill[i])
+         ra_set_node_spill_cost(g, i, spill_costs[i]);
+   }
+
+   return ra_get_best_spill_node(g);
+}
+
+void
+vec4_visitor::spill_reg(int spill_reg_nr)
+{
+   assert(virtual_grf_sizes[spill_reg_nr] == 1);
+   unsigned int spill_offset = c->last_scratch++;
+
+   /* Generate spill/unspill instructions for the objects being spilled. */
+   foreach_list(node, &this->instructions) {
+      vec4_instruction *inst = (vec4_instruction *) node;
+
+      for (unsigned int i = 0; i < 3; i++) {
+         if (inst->src[i].file == GRF && inst->src[i].reg == spill_reg_nr) {
+            src_reg spill_reg = inst->src[i];
+            inst->src[i].reg = virtual_grf_alloc(1);
+            dst_reg temp = dst_reg(inst->src[i]);
+
+            /* Only read the necessary channels, to avoid overwriting the rest
+             * with data that may not have been written to scratch.
+             */
+            temp.writemask = 0;
+            for (int c = 0; c < 4; c++)
+               temp.writemask |= (1 << BRW_GET_SWZ(inst->src[i].swizzle, c));
+            assert(temp.writemask != 0);
+
+            emit_scratch_read(inst, temp, spill_reg, spill_offset);
+         }
+      }
+
+      if (inst->dst.file == GRF && inst->dst.reg == spill_reg_nr) {
+         dst_reg spill_reg = inst->dst;
+         inst->dst.reg = virtual_grf_alloc(1);
+
+         /* We don't want a swizzle when reading from the source; read the
+          * whole register and use spill_reg's writemask to select which
+          * channels to write.
+          */
+         src_reg temp = src_reg(inst->dst);
+         temp.swizzle = BRW_SWIZZLE_XYZW;
+         emit_scratch_write(inst, temp, spill_reg, spill_offset);
+      }
+   }
+
+   this->live_intervals_valid = false;
+}
+
 } /* namespace brw */