i965/vec4: Ignore swizzle of VGRF for use by var_range_end().

var_range_end(v, n) loops over the n components of variable number v and
finds the maximum value, giving the last use of any component of v.
Therefore it expects v to correspond to the variable associated with the
.x channel of the VGRF.

var_from_reg() however returns the variable for the first channel of the
VGRF, post-swizzle.

So, if the last register had a swizzle with y, z, or w in the swizzle
component, we would read out of bounds. For any other register, we would
read liveness information from the next register.

The fix is to convert the src_reg to a dst_reg in order to call the
dst_reg version of var_from_reg() that doesn't consider the swizzle.

Cc: mesa-stable@lists.freedesktop.org
Reviewed-by: Francisco Jerez <currojerez@riseup.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/drivers/dri/i965/brw_vec4.cpp

@@ -1111,7 +1111,7 @@ vec4_visitor::opt_register_coalesce()
       /* Can't coalesce this GRF if someone else was going to
        * read it later.
        */
-      if (var_range_end(var_from_reg(alloc, inst->src[0]), 4) > ip)
+      if (var_range_end(var_from_reg(alloc, dst_reg(inst->src[0])), 4) > ip)
 	 continue;
 
       /* We need to check interference with the final destination between this

src/mesa/drivers/dri/i965/brw_vec4_cse.cpp

@@ -246,7 +246,7 @@ vec4_visitor::opt_cse_local(bblock_t *block)
              * more -- a sure sign they'll fail operands_match().
              */
             if (src->file == VGRF) {
-               if (var_range_end(var_from_reg(alloc, *src), 4) < ip) {
+               if (var_range_end(var_from_reg(alloc, dst_reg(*src)), 4) < ip) {
                   entry->remove();
                   ralloc_free(entry);
                   break;