intel/brw: Combine constants and constant propagation for CSEL

No shader-db or fossil-db changes on any Intel platform. This ends up
begin helpful in "intel/brw: Use range analysis to optimize fsign."

v2: Add integer CSEL support

v3: Massive simplification (-20 lines!) of constant propagation
logic. Suggested by Ken. Add missing CSEL case in supports_src_as_imm.
Noticed by Ken.

v4: While MAD can mix F and HF sources on some platforms, CSEL
cannot. Found by skqp on TGL.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org> [v3]
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/29095>

src/intel/compiler/brw_fs_combine_constants.cpp

@@ -999,6 +999,10 @@ supports_src_as_imm(const struct intel_device_info *devinfo, const fs_inst *inst
       /* ADD3 only exists on Gfx12.5+. */
       return true;
 
+   case BRW_OPCODE_CSEL:
+      /* While MAD can mix F and HF sources on some platforms, CSEL cannot. */
+      return inst->src[0].type != BRW_TYPE_F;
+
    case BRW_OPCODE_MAD:
       /* Integer types can always mix sizes. Floating point types can mix
        * sizes on Gfx12. On Gfx12.5, floating point sources must all be HF or
@@ -1301,7 +1305,15 @@ brw_fs_opt_combine_constants(fs_visitor &s)
          }
          break;
 
+      /* FINISHME: CSEL handling could be better. For some cases, src[0] and
+       * src[1] can be commutative (e.g., any integer comparison). In those
+       * cases when src[1] is IMM, the sources could be exchanged. In
+       * addition, when both sources are IMM that could be represented as
+       * 16-bits, it would be better to add both sources with
+       * allow_one_constant=true as is done for SEL.
+       */
       case BRW_OPCODE_ADD3:
+      case BRW_OPCODE_CSEL:
       case BRW_OPCODE_MAD: {
          for (int i = 0; i < inst->sources; i++) {
             if (inst->src[i].file != IMM)

src/intel/compiler/brw_fs_copy_propagation.cpp

@@ -1168,6 +1168,29 @@ try_constant_propagate(const brw_compiler *compiler, fs_inst *inst,
       }
       break;
 
+   case BRW_OPCODE_CSEL:
+      assert(inst->conditional_mod != BRW_CONDITIONAL_NONE);
+
+      if (arg == 0 &&
+          inst->src[1].file != IMM &&
+          (!brw_type_is_float(inst->src[1].type) ||
+           inst->conditional_mod == BRW_CONDITIONAL_NZ ||
+           inst->conditional_mod == BRW_CONDITIONAL_Z)) {
+         /* Only EQ and NE are commutative due to NaN issues. */
+         inst->src[0] = inst->src[1];
+         inst->src[1] = val;
+         inst->conditional_mod = brw_negate_cmod(inst->conditional_mod);
+      } else {
+         /* While CSEL is a 3-source instruction, the last source should never
+          * be a constant.  We'll support that, but should it ever happen, we
+          * should add support to the constant folding pass.
+          */
+         inst->src[arg] = val;
+      }
+
+      progress = true;
+      break;
+
    case FS_OPCODE_FB_WRITE_LOGICAL:
       /* The stencil and omask sources of FS_OPCODE_FB_WRITE_LOGICAL are
        * bit-cast using a strided region so they cannot be immediates.