nir/algebraic: support for power-of-two optimizations

Some optimizations, like converting integer multiply/divide into left/
right shifts, have additional constraints on the search expression.
Like requiring that a variable is a constant power of two.  Support
these cases by allowing a fxn name to be appended to the search var
expression (ie. "a#32(is_power_of_two)").

Signed-off-by: Rob Clark <robclark@freedesktop.org>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

src/compiler/nir/nir.h

@@ -1651,6 +1651,9 @@ typedef struct nir_shader_compiler_options {
    /* lower {slt,sge,seq,sne} to {flt,fge,feq,fne} + b2f: */
    bool lower_scmp;
 
+   /** enables rules to lower idiv by power-of-two: */
+   bool lower_idiv;
+
    /* Does the native fdot instruction replicate its result for four
     * components?  If so, then opt_algebraic_late will turn all fdotN
     * instructions into fdot_replicatedN instructions.