On Mon, 8 Jun 2015, Marek Polacek wrote:
PR tree-optimization/66299 * match.pd ((CST1 << A) == CST2 -> A == ctz (CST2) - ctz (CST1) ((CST1 << A) != CST2 -> A != ctz (CST2) - ctz (CST1)): New
You are braver than I am, I would have abbreviated ctz (CST2) - ctz (CST1) to CST3 in the ChangeLog ;-)
+/* (CST1 << A) == CST2 -> A == ctz (CST2) - ctz (CST1) + (CST1 << A) != CST2 -> A != ctz (CST2) - ctz (CST1) + if CST2 != 0. */ +(for cmp (ne eq) + (simplify + (cmp (lshift INTEGER_CST@0 @1) INTEGER_CST@2) + (with { + unsigned int cand = wi::ctz (@2) - wi::ctz (@0); } + (if (!integer_zerop (@2)
You can probably use directly wi::ne_p (@2, 0) here. Shouldn't this be indented one space more?
+ && wi::eq_p (wi::lshift (@0, cand), @2)) + (cmp @1 { build_int_cst (TREE_TYPE (@1), cand); })))))
Making 'cand' signed, you could return 0 when cand<0, like (2<<x)==1. You could also return 0 when the candidate turns out not to work: (3<<x)==4. Tweaking it so that (6<<X)==0 becomes X>=31 for TYPE_OVERFLOW_WRAPS and false for TYPE_OVERFLOW_UNDEFINED is probably more controversial. FWIW, the patch looks good to me, thanks. -- Marc Glisse