intel/compiler: Make decision based on source type instead of opcode

This patch restructure code a little bit to check if source can be
represented as immediate operand. This is a foundation for next patch
which add checks for integer operand as well.

Suggested-by: Jason Ekstrand <jason@jlekstrand.net>
Signed-off-by: Sagar Ghuge <sagar.ghuge@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11596>

src/intel/compiler/brw_fs_combine_constants.cpp

@@ -336,20 +336,41 @@ representable_as_hf(float f, uint16_t *hf)
 }
 
 static bool
-represent_src_as_imm(const struct intel_device_info *devinfo,
+supports_src_as_imm(const struct intel_device_info *devinfo, enum opcode op)
-                     fs_reg *src)
 {
+   switch (op) {
+   case BRW_OPCODE_MAD:
+      return devinfo->ver == 12 && devinfo->verx10 < 125;
+   default:
+      return false;
+   }
+}
+
+static bool
+can_promote_src_as_imm(const struct intel_device_info *devinfo, fs_inst *inst,
+                       unsigned src_idx)
+{
+   /* Experiment shows that we can only support src0 as immediate */
+   if (src_idx != 0)
+      return false;
+
+   if (!supports_src_as_imm(devinfo, inst->opcode))
+      return false;
+
    /* TODO - Fix the codepath below to use a bfloat16 immediate on XeHP,
     *        since HF/F mixed mode has been removed from the hardware.
     */
-   if (devinfo->ver == 12 && devinfo->verx10 < 125) {
+   switch(inst->src[src_idx].type) {
+   case BRW_REGISTER_TYPE_F: {
       uint16_t hf;
-      if (representable_as_hf(src->f, &hf)) {
+      if (representable_as_hf(inst->src[src_idx].f, &hf)) {
-         *src = retype(brw_imm_uw(hf), BRW_REGISTER_TYPE_HF);
+         inst->src[src_idx] = retype(brw_imm_uw(hf), BRW_REGISTER_TYPE_HF);
          return true;
       }
    }
-   return false;
+   default:
+      return false;
+   }
 }
 
 bool
@@ -375,17 +396,12 @@ fs_visitor::opt_combine_constants()
       if (!could_coissue(devinfo, inst) && !must_promote_imm(devinfo, inst))
          continue;
 
-      bool represented_as_imm = false;
       for (int i = 0; i < inst->sources; i++) {
          if (inst->src[i].file != IMM)
             continue;
 
-         if (!represented_as_imm && i == 0 &&
+         if (can_promote_src_as_imm(devinfo, inst, i))
-             inst->opcode == BRW_OPCODE_MAD &&
-             represent_src_as_imm(devinfo, &inst->src[i])) {
-            represented_as_imm = true;
             continue;
-         }
 
          char data[8];
          brw_reg_type type;