nir/algebraic: Add helpers and a rule involving wrapping

The helpers are needed so we can use the syntax `instr(cond)` in the
algebraic rules.  Add simple rule for dropping a pair of mul-div of
the same value when wrapping is guaranteed to not happen.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

src/compiler/nir/nir_opt_algebraic.py

@@ -761,6 +761,9 @@ optimizations.extend([
    (('~fadd', '#a', ('fneg', ('fadd', 'b(is_not_const)', '#c'))), ('fadd', ('fadd', a, ('fneg', c)), ('fneg', b))),
    (('iadd', '#a', ('iadd', 'b(is_not_const)', '#c')), ('iadd', ('iadd', a, c), b)),
 
+   # Drop mul-div by the same value when there's no wrapping.
+   (('idiv', ('imul(no_signed_wrap)', a, b), b), a),
+
    # By definition...
    (('bcsel', ('ige', ('find_lsb', a), 0), ('find_lsb', a), -1), ('find_lsb', a)),
    (('bcsel', ('ige', ('ifind_msb', a), 0), ('ifind_msb', a), -1), ('ifind_msb', a)),

src/compiler/nir/nir_search_helpers.h

@@ -288,4 +288,16 @@ is_lower_half_zero(nir_alu_instr *instr, unsigned src,
    return true;
 }
 
+static inline bool
+no_signed_wrap(nir_alu_instr *instr)
+{
+   return instr->no_signed_wrap;
+}
+
+static inline bool
+no_unsigned_wrap(nir_alu_instr *instr)
+{
+   return instr->no_unsigned_wrap;
+}
+
 #endif /* _NIR_SEARCH_ */