i965: Don't spill "smeared" registers.

Fixes an assertion failure when compiling certain shaders that need both
pull constants and register spilling:

brw_eu_emit.c:204: validate_reg: Assertion `execsize >= width' failed.

NOTE: This is a candidate for release branches.

Signed-off-by: Paul Berry <stereotype441@gmail.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/drivers/dri/i965/brw_fs_reg_allocate.cpp

@@ -317,11 +317,26 @@ fs_visitor::choose_spill_reg(struct ra_graph *g)
       for (unsigned int i = 0; i < 3; i++) {
 	 if (inst->src[i].file == GRF) {
 	    spill_costs[inst->src[i].reg] += loop_scale;
+
+            /* Register spilling logic assumes full-width registers; smeared
+             * registers have a width of 1 so if we try to spill them we'll
+             * generate invalid assembly.  This shouldn't be a problem because
+             * smeared registers are only used as short-term temporaries when
+             * loading pull constants, so spilling them is unlikely to reduce
+             * register pressure anyhow.
+             */
+            if (inst->src[i].smear >= 0) {
+               no_spill[inst->src[i].reg] = true;
+            }
 	 }
       }
 
       if (inst->dst.file == GRF) {
 	 spill_costs[inst->dst.reg] += inst->regs_written() * loop_scale;
+
+         if (inst->dst.smear >= 0) {
+            no_spill[inst->dst.reg] = true;
+         }
       }
 
       switch (inst->opcode) {