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From: Jeff Law <law@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org Subject: [gcc r12-5011] Minor optimization of variable bit testing Date: Tue, 9 Nov 2021 04:25:36 +0000 (GMT) [thread overview] Message-ID: <20211109042536.D8AD83858405@sourceware.org> (raw) https://gcc.gnu.org/g:2abd924f91e54a5229efb2c3bb5fb247059a5b37 commit r12-5011-g2abd924f91e54a5229efb2c3bb5fb247059a5b37 Author: Jeff Law <jeffreyalaw@gmail.com> Date: Mon Nov 8 23:23:34 2021 -0500 Minor optimization of variable bit testing gcc/ * match.pd: New pattern to simplify (1 << n) & M ==/!= 0 for M being a power of 2. gcc/testsuite * gcc.dg/tree-ssa/bittest.c: New test Diff: --- gcc/match.pd | 11 +++++++++++ gcc/testsuite/gcc.dg/tree-ssa/bittest.c | 27 +++++++++++++++++++++++++++ 2 files changed, 38 insertions(+) diff --git a/gcc/match.pd b/gcc/match.pd index 71cf6f9df0a..cdab5e59f4e 100644 --- a/gcc/match.pd +++ b/gcc/match.pd @@ -3441,6 +3441,17 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT) (bit_and (convert (shift:shift_type (convert @3) @1)) { newmaskt; }) (bit_and @4 { newmaskt; }))))))))))))) +/* ((1 << n) & M) != 0 -> n == log2 (M) */ +(for cmp (ne eq) + icmp (eq ne) + (simplify + (cmp + (bit_and + (nop_convert? (lshift integer_onep @0)) integer_pow2p@1) integer_zerop) + (if (INTEGRAL_TYPE_P (TREE_TYPE (@0))) + (icmp @0 { wide_int_to_tree (TREE_TYPE (@0), + wi::exact_log2 (wi::to_wide (@1))); })))) + /* Fold (X {&,^,|} C2) << C1 into (X << C1) {&,^,|} (C2 << C1) (X {&,^,|} C2) >> C1 into (X >> C1) & (C2 >> C1). */ (for shift (lshift rshift) diff --git a/gcc/testsuite/gcc.dg/tree-ssa/bittest.c b/gcc/testsuite/gcc.dg/tree-ssa/bittest.c new file mode 100644 index 00000000000..7d712cad1ee --- /dev/null +++ b/gcc/testsuite/gcc.dg/tree-ssa/bittest.c @@ -0,0 +1,27 @@ +/* { dg-do compile } */ +/* { dg-options "-O2 -fdump-tree-optimized" } */ + + +void bar (void); + +void +foo(unsigned int abc123) +{ + unsigned int xyzpdq = (1 << abc123); + if ((xyzpdq & 0x800) != 0) + bar(); +} + +void +baz(unsigned int abc123) +{ + unsigned int xyzpdq = (1 << abc123); + if ((xyzpdq & 0x800) == 0) + bar(); +} + +/* What we want to verify is that the bit test against xyzpdq is + replaced with a test against abc123 which avoids the shifting + and bit ops. */ +/* { dg-final { scan-tree-dump-not "xyzpdq" "optimized"} } */ +/* { dg-final { scan-tree-dump-times "if .abc123" 2 "optimized"} } */
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