On Mon, 25 Jul 2022, H.J. Lu wrote: > On Fri, Jul 22, 2022 at 11:10 PM Richard Biener via Gcc-patches > <gcc-patches@gcc.gnu.org> wrote: > > > > > > > > > Am 22.07.2022 um 22:17 schrieb H.J. Lu via Gcc-patches > > > <gcc-patches@gcc.gnu.org>: > > > > > > On Thu, Jul 21, 2022 at 4:24 AM Richard Biener via Gcc-patches > > > <gcc-patches@gcc.gnu.org> wrote: > > >> > > >> The following makes sure to fold ~(a ^ b) to a == b for truth > > >> values (but not vectors, we'd have to check for vector support of > > >> equality). That turns the PR106379 testcase into a ranger one. > > >> > > >> Note that while we arrive at ~(a ^ b) in a convoluted way from > > >> original !a == !b one can eventually write the expression this > > >> way directly as well. > > >> > > >> Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed. > > >> > > >> PR tree-optimization/106379 > > >> * match.pd (~(a ^ b) -> a == b): New pattern. > > >> > > >> * gcc.dg/pr106379-1.c: New testcase. > > >> --- > > >> gcc/match.pd | 6 ++++++ > > >> gcc/testsuite/gcc.dg/pr106379-1.c | 9 +++++++++ > > >> 2 files changed, 15 insertions(+) > > >> create mode 100644 gcc/testsuite/gcc.dg/pr106379-1.c > > >> > > >> diff --git a/gcc/match.pd b/gcc/match.pd > > >> index 8bbc0dbd5cd..88a1a5aa9cc 100644 > > >> --- a/gcc/match.pd > > >> +++ b/gcc/match.pd > > >> @@ -1938,6 +1938,12 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT) > > >> (if (tree_nop_conversion_p (type, TREE_TYPE (@0))) > > >> (bit_not (bit_xor (view_convert @0) @1)))) > > >> > > >> +/* ~(a ^ b) is a == b for truth valued a and b. */ > > >> +(simplify > > >> + (bit_not (bit_xor:s truth_valued_p@0 truth_valued_p@1)) > > >> + (if (!VECTOR_TYPE_P (type)) > > >> + (convert (eq @0 @1)))) > > > > > > For integers, isn't it wrong to convert ~(boolean exp) to boolean exp? > > > > That’s what the (convert. …) should compensate for? > > Is ~(boolean exp) == ~((int) (boolean exp)) or (int) (~(boolean exp))?
Depends on what 'boolean exp' is, and as PR106414 shows I was wrong because in C a == b has type 'int' and not type bool but we consider it "boolean". There of course ~(a == b) is not equal to a != b. Richard.
