nir: Use the flrp lowering pass instead of nir_opt_algebraic

I tried to be very careful while updating all the various drivers, but I
don't have any of that hardware for testing. :(

i965 is the only platform that sets always_precise = true, and it is
only set true for fragment shaders.  Gen4 and Gen5 both set lower_flrp32
only for vertex shaders.  For fragment shaders, nir_op_flrp is lowered
during code generation as a(1-c)+bc.  On all other platforms 64-bit
nir_op_flrp and on Gen11 32-bit nir_op_flrp are lowered using the old
nir_opt_algebraic method.

No changes on any other Intel platforms.

v2: Add panfrost changes.

Iron Lake and GM45 had similar results. (Iron Lake shown)
total cycles in shared programs: 188647754 -> 188647748 (<.01%)
cycles in affected programs: 5096 -> 5090 (-0.12%)
helped: 3
HURT: 0
helped stats (abs) min: 2 max: 2 x̄: 2.00 x̃: 2
helped stats (rel) min: 0.12% max: 0.12% x̄: 0.12% x̃: 0.12%

Reviewed-by: Matt Turner <[email protected]>

1 files changed, 21 insertions, 0 deletions

diff --git a/src/freedreno/ir3/ir3_nir.c b/src/freedreno/ir3/ir3_nir.c
index 3bc22fe5be5..744fd958fc6 100644
--- a/src/freedreno/ir3/ir3_nir.c
+++ b/src/freedreno/ir3/ir3_nir.c
@@ -112,6 +112,11 @@ static void
 ir3_optimize_loop(nir_shader *s)
 {
 	bool progress;
+	unsigned lower_flrp =
+		(s->options->lower_flrp16 ? 16 : 0) |
+		(s->options->lower_flrp32 ? 32 : 0) |
+		(s->options->lower_flrp64 ? 64 : 0);
+
 	do {
 		progress = false;
 
@@ -135,6 +140,22 @@ ir3_optimize_loop(nir_shader *s)
 		progress |= OPT(s, nir_opt_intrinsics);
 		progress |= OPT(s, nir_opt_algebraic);
 		progress |= OPT(s, nir_opt_constant_folding);
+
+		if (lower_flrp != 0) {
+			if (OPT(s, nir_lower_flrp,
+					lower_flrp,
+					false /* always_precise */,
+					s->options->lower_ffma)) {
+				OPT(s, nir_opt_constant_folding);
+				progress = true;
+			}
+
+			/* Nothing should rematerialize any flrps, so we only
+			 * need to do this lowering once.
+			 */
+			lower_flrp = 0;
+		}
+
 		progress |= OPT(s, nir_opt_dead_cf);
 		if (OPT(s, nir_opt_trivial_continues)) {
 			progress |= true;