[Bug tree-optimization/101610] CST - (x ^ (CST-1)) can be optimized to x + 1 if x < CST and CST is a power of 2
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101610 Andrew Pinski changed: What|Removed |Added Status|ASSIGNED|RESOLVED Resolution|--- |DUPLICATE --- Comment #4 from Andrew Pinski --- This is basically PR 91213. *** This bug has been marked as a duplicate of bug 91213 ***
[Bug tree-optimization/101610] CST - (x ^ (CST-1)) can be optimized to x + 1 if x < CST and CST is a power of 2
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101610 --- Comment #3 from Andrew Pinski --- (In reply to Andrew Pinski from comment #2) > So looking at this one (and one which I just assigned myself): > unsigned long f(unsigned long x) > { > if (x >= 64)__builtin_unreachable(); > x = x ^ 63; > unsigned long y = x; ;; Range is still [0,63] > unsigned long z = 64 - y; ;; is similar to (63 - y) +1 -> (y ^ 63) + 1 -> x > + 1 > return z; > } > > So mine: > > Something like: > (simplify > (minus INTEGER_CST@0 SSA_NAME@1) > (if (exact_power2(@0) && get_nonzero_bits(@1) == (@0 - 1) > (add (bit_xor! @1 @0) {build_one_cst (type); })) But I don't think this should be done at the gimple level unless we have a place were we decide it should be considered "lowered gimple". I will be doing a simplify-rtx.c patch for this case which should get some code generation improvement but not with the original case as we need to export the non-zero bits down from gimple to RTL still (though I hear someone is working on keeping around the non-zero bits around through out the whole RTL phase).
[Bug tree-optimization/101610] CST - (x ^ (CST-1)) can be optimized to x + 1 if x < CST and CST is a power of 2
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101610 Andrew Pinski changed: What|Removed |Added See Also||https://gcc.gnu.org/bugzill ||a/show_bug.cgi?id=96921 Status|UNCONFIRMED |ASSIGNED Last reconfirmed||2021-07-28 Ever confirmed|0 |1 Assignee|unassigned at gcc dot gnu.org |pinskia at gcc dot gnu.org --- Comment #2 from Andrew Pinski --- So looking at this one (and one which I just assigned myself): unsigned long f(unsigned long x) { if (x >= 64)__builtin_unreachable(); x = x ^ 63; unsigned long y = x; ;; Range is still [0,63] unsigned long z = 64 - y; ;; is similar to (63 - y) +1 -> (y ^ 63) + 1 -> x + 1 return z; } So mine: Something like: (simplify (minus INTEGER_CST@0 SSA_NAME@1) (if (exact_power2(@0) && get_nonzero_bits(@1) == (@0 - 1) (add (bit_xor! @1 @0) {build_one_cst (type); }))
[Bug tree-optimization/101610] CST - (x ^ (CST-1)) can be optimized to x + 1 if x < CST and CST is a power of 2
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101610 --- Comment #1 from Andrew Pinski --- I noticed this while looking into PR 78103.