elk: Increase the size of some structure fields in combine_constants

In very large shaders, first_use_ip, last_use_ip, and even (register) nr
can overflow 16 bits. Increase the size of these fields.  Some structure
components are rearranged to promote better packing.

Fixes: 2dad1e3abd ("i965/fs: Add pass to combine immediates.")
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@intel.com>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/37482>

src/intel/compiler/elk/elk_fs_combine_constants.cpp

@@ -861,13 +861,6 @@ struct imm {
    /** When promoting half-float we need to account for certain restrictions */
    bool is_half_float;
 
-   /**
-    * The GRF register and subregister number where we've decided to store the
-    * constant value.
-    */
-   uint8_t subreg_offset;
-   uint16_t nr;
-
    /** The number of coissuable instructions using this immediate. */
    uint16_t uses_by_coissue;
 
@@ -880,8 +873,15 @@ struct imm {
    /** Is the value used only in a single basic block? */
    bool used_in_single_block;
 
-   uint16_t first_use_ip;
-   uint16_t last_use_ip;
+   /**
+    * The GRF register and subregister number where we've decided to store the
+    * constant value.
+    */
+   uint8_t subreg_offset;
+   uint32_t nr;
+
+   uint32_t first_use_ip;
+   uint32_t last_use_ip;
 };
 
 /** The working set of information about immediates. */
@@ -1347,7 +1347,7 @@ elk_fs_visitor::opt_combine_constants()
       imm->must_promote = false;
       imm->is_half_float = false;
 
-      imm->first_use_ip = UINT16_MAX;
+      imm->first_use_ip = UINT32_MAX;
       imm->last_use_ip = 0;
 
       imm->uses = new(const_ctx) brw_exec_list;