pan/mdg: Emit fcsel when beneficial

If there are floating point modifiers, we emit fcsel instead of icsel
(and likewise if integer modifiers, icsel instead of fcsel) to minimize
redundant instructions.

total instructions in shared programs: 3628 -> 3626 (-0.06%)
instructions in affected programs: 139 -> 137 (-1.44%)
helped: 2
HURT: 0

total bundles in shared programs: 1886 -> 1885 (-0.05%)
bundles in affected programs: 19 -> 18 (-5.26%)
helped: 1
HURT: 0

total quadwords in shared programs: 3319 -> 3317 (-0.06%)
quadwords in affected programs: 127 -> 125 (-1.57%)
helped: 2
HURT: 0

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5123>

src/panfrost/midgard/midgard_compile.c

@@ -657,6 +657,57 @@ mir_copy_src(midgard_instruction *ins, nir_alu_instr *instr, unsigned i, unsigne
         }
 }
 
+/* Midgard features both fcsel and icsel, depending on whether you want int or
+ * float modifiers. NIR's csel is typeless, so we want a heuristic to guess if
+ * we should emit an int or float csel depending on what modifiers could be
+ * placed. In the absense of modifiers, this is probably arbitrary. */
+
+static bool
+mir_is_bcsel_float(nir_alu_instr *instr)
+{
+        nir_op intmods[] = {
+                nir_op_i2i8, nir_op_i2i16,
+                nir_op_i2i32, nir_op_i2i64
+        };
+
+        nir_op floatmods[] = {
+                nir_op_fabs, nir_op_fneg,
+                nir_op_f2f16, nir_op_f2f32,
+                nir_op_f2f64
+        };
+
+        nir_op floatdestmods[] = {
+                nir_op_fsat, nir_op_fsat_signed, nir_op_fclamp_pos,
+                nir_op_f2f16, nir_op_f2f32
+        };
+
+        signed score = 0;
+
+        for (unsigned i = 1; i < 3; ++i) {
+                nir_alu_src s = instr->src[i];
+                for (unsigned q = 0; q < ARRAY_SIZE(intmods); ++q) {
+                        if (pan_has_source_mod(&s, intmods[q]))
+                                score--;
+                }
+        }
+
+        for (unsigned i = 1; i < 3; ++i) {
+                nir_alu_src s = instr->src[i];
+                for (unsigned q = 0; q < ARRAY_SIZE(floatmods); ++q) {
+                        if (pan_has_source_mod(&s, floatmods[q]))
+                                score++;
+                }
+        }
+
+        for (unsigned q = 0; q < ARRAY_SIZE(floatdestmods); ++q) {
+                nir_dest *dest = &instr->dest.dest;
+                if (pan_has_dest_mod(&dest, floatdestmods[q]))
+                        score++;
+        }
+
+        return (score > 0);
+}
+
 static void
 emit_alu(compiler_context *ctx, nir_alu_instr *instr)
 {
@@ -878,17 +929,11 @@ emit_alu(compiler_context *ctx, nir_alu_instr *instr)
         }
 
         case nir_op_b32csel: {
-                /* Midgard features both fcsel and icsel, depending on
-                 * the type of the arguments/output. However, as long
-                 * as we're careful we can _always_ use icsel and
-                 * _never_ need fcsel, since the latter does additional
-                 * floating-point-specific processing whereas the
-                 * former just moves bits on the wire. It's not obvious
-                 * why these are separate opcodes, save for the ability
-                 * to do things like sat/pos/abs/neg for free */
-
                 bool mixed = nir_is_non_scalar_swizzle(&instr->src[0], nr_components);
-                op = mixed ? midgard_alu_op_icsel_v : midgard_alu_op_icsel;
+                bool is_float = mir_is_bcsel_float(instr);
+                op = is_float ?
+                        (mixed ? midgard_alu_op_fcsel_v : midgard_alu_op_fcsel) :
+                        (mixed ? midgard_alu_op_icsel_v : midgard_alu_op_icsel);
 
                 break;
         }