intel/fs: Use the original destination region for int MUL lowering

Some hardware (CHV, BXT) have special restrictions on register regions
when doing integer multiplication.  We want to respect those when we
lower to DxW multiplication.

Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Cc: mesa-stable@lists.freedesktop.org

src/intel/compiler/brw_fs.cpp

@@ -3489,18 +3489,20 @@ fs_visitor::lower_integer_multiplication()
 
             bool needs_mov = false;
             fs_reg orig_dst = inst->dst;
+            fs_reg low = inst->dst;
             if (orig_dst.is_null() || orig_dst.file == MRF ||
                 regions_overlap(inst->dst, inst->size_written,
                                 inst->src[0], inst->size_read(0)) ||
                 regions_overlap(inst->dst, inst->size_written,
                                 inst->src[1], inst->size_read(1))) {
                needs_mov = true;
-               inst->dst = fs_reg(VGRF, alloc.allocate(dispatch_width / 8),
-                                  inst->dst.type);
+               low.nr = alloc.allocate(regs_written(inst));
+               low.offset = low.offset % REG_SIZE;
             }
-            fs_reg low = inst->dst;
-            fs_reg high(VGRF, alloc.allocate(dispatch_width / 8),
-                        inst->dst.type);
+
+            fs_reg high = inst->dst;
+            high.nr = alloc.allocate(regs_written(inst));
+            high.offset = high.offset % REG_SIZE;
 
             if (devinfo->gen >= 7) {
                if (inst->src[1].file == IMM) {
@@ -3521,13 +3523,13 @@ fs_visitor::lower_integer_multiplication()
                         inst->src[1]);
             }
 
-            ibld.ADD(subscript(inst->dst, BRW_REGISTER_TYPE_UW, 1),
+            ibld.ADD(subscript(low, BRW_REGISTER_TYPE_UW, 1),
                      subscript(low, BRW_REGISTER_TYPE_UW, 1),
                      subscript(high, BRW_REGISTER_TYPE_UW, 0));
 
             if (needs_mov || inst->conditional_mod) {
                set_condmod(inst->conditional_mod,
-                           ibld.MOV(orig_dst, inst->dst));
+                           ibld.MOV(orig_dst, low));
             }
          }