i965/fs: Use per-channel interference for register_coalesce_2().

This will let us coalesce into texture-from-GRF arguments, which would
otherwise be prevented due to the live interval for the whole vgrf
extending across all the MOVs setting up the channels of the message

v2 (Kenneth Graunke): Rebase for renames.

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

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

@@ -2063,11 +2063,16 @@ fs_visitor::register_coalesce_2()
 	  inst->src[0].smear != -1 ||
 	  inst->dst.file != GRF ||
 	  inst->dst.type != inst->src[0].type ||
-	  virtual_grf_sizes[inst->src[0].reg] != 1 ||
-	  virtual_grf_interferes(inst->dst.reg, inst->src[0].reg)) {
+	  virtual_grf_sizes[inst->src[0].reg] != 1) {
 	 continue;
       }
 
+      int var_from = live_intervals->var_from_reg(&inst->src[0]);
+      int var_to = live_intervals->var_from_reg(&inst->dst);
+
+      if (live_intervals->vars_interfere(var_from, var_to))
+         continue;
+
       int reg_from = inst->src[0].reg;
       assert(inst->src[0].reg_offset == 0);
       int reg_to = inst->dst.reg;
@@ -2091,31 +2096,13 @@ fs_visitor::register_coalesce_2()
       }
 
       inst->remove();
-
-      /* We don't need to recalculate live intervals inside the loop despite
-       * invalidating them; we only use them for the interferes test, and we
-       * must have had a situation where the intervals were:
-       *
-       *  from  to
-       *  ^
-       *  |
-       *  v
-       *        ^
-       *        |
-       *        v
-       *
-       * Some register R that might get coalesced with one of these two could
-       * only be referencing "to", otherwise "from"'s range would have been
-       * longer.  R's range could also only start at the end of "to" or later,
-       * otherwise it will conflict with "to" when we try to coalesce "to"
-       * into Rw anyway.
-       */
-      invalidate_live_intervals();
-
       progress = true;
       continue;
    }
 
+   if (progress)
+      invalidate_live_intervals();
+
    return progress;
 }
 

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

@@ -244,6 +244,12 @@ fs_live_variables::compute_start_end()
    }
 }
 
+int
+fs_live_variables::var_from_reg(fs_reg *reg)
+{
+   return var_from_vgrf[reg->reg] + reg->reg_offset;
+}
+
 fs_live_variables::fs_live_variables(fs_visitor *v, cfg_t *cfg)
    : v(v), cfg(cfg)
 {
@@ -334,6 +340,13 @@ fs_visitor::calculate_live_intervals()
    }
 }
 
+bool
+fs_live_variables::vars_interfere(int a, int b)
+{
+   return !(end[b] <= start[a] ||
+            end[a] <= start[b]);
+}
+
 bool
 fs_visitor::virtual_grf_interferes(int a, int b)
 {

src/mesa/drivers/dri/i965/brw_fs_live_variables.h

@@ -66,6 +66,9 @@ public:
    void compute_live_variables();
    void compute_start_end();
 
+   bool vars_interfere(int a, int b);
+   int var_from_reg(fs_reg *reg);
+
    fs_visitor *v;
    cfg_t *cfg;
    void *mem_ctx;