nir: Add optional lowering of flrp.

Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>

src/glsl/nir/nir.h

@@ -1365,6 +1365,7 @@ typedef struct nir_function {
 
 typedef struct nir_shader_compiler_options {
    bool lower_ffma;
+   bool lower_flrp;
    bool lower_fpow;
    bool lower_fsat;
    bool lower_fsqrt;

src/glsl/nir/nir_opt_algebraic.py

@@ -75,6 +75,7 @@ optimizations = [
    (('flrp', a, b, 1.0), b),
    (('flrp', a, a, b), a),
    (('flrp', 0.0, a, b), ('fmul', a, b)),
+   (('flrp', a, b, c), ('fadd', ('fmul', c, ('fsub', b, a)), a), 'options->lower_flrp'),
    (('ffma', a, b, c), ('fadd', ('fmul', a, b), c), 'options->lower_ffma'),
    (('fadd', ('fmul', a, b), c), ('ffma', a, b, c), '!options->lower_ffma'),
    # Comparison simplifications