nir: add fisnormal lowering

just lower the 32-bit version for now.

Thanks to alyssa for this suggested lowering.

Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12207>

src/compiler/nir/nir.h

@@ -3427,6 +3427,8 @@ typedef struct nir_shader_compiler_options {
    bool lower_fneg;
    /** lowers ineg to isub. Driver must call nir_opt_algebraic_late(). */
    bool lower_ineg;
+   /** lowers fisnormal to alu ops. */
+   bool lower_fisnormal;
 
    /* lower {slt,sge,seq,sne} to {flt,fge,feq,fneu} + b2f: */
    bool lower_scmp;

src/compiler/nir/nir_opt_algebraic.py

@@ -2143,6 +2143,10 @@ for op in ['ineg', 'iabs', 'inot', 'isign']:
         ((op, ('bcsel', c, '#a', '#b')), ('bcsel', c, (op, a), (op, b))),
     ]
 
+optimizations.extend([
+    (('fisnormal', 'a@32'), ('ult', 0x1ffffff, ('iadd', ('ishl', a, 1), 0x1000000)), 'options->lower_fisnormal')
+    ])
+
 # This section contains optimizations to propagate downsizing conversions of
 # constructed vectors into vectors of downsized components. Whether this is
 # useful depends on the SIMD semantics of the backend. On a true SIMD machine,