https://gcc.gnu.org/g:e1f56c67a82172730c377a96a46e8d75445e6a48
commit r15-274-ge1f56c67a82172730c377a96a46e8d75445e6a48 Author: Stefan Schulze Frielinghaus <stefa...@linux.ibm.com> Date: Tue May 7 14:12:55 2024 +0200 tree-optimization/110490 - bitcount for narrow modes Bitcount operations popcount, clz, and ctz are emulated for narrow modes in case an operation is only supported for wider modes. Beside that ctz may be emulated via clz in expand_ctz. Reflect this in expression_expensive_p. I considered the emulation of ctz via clz as not expensive since this basically reduces to ctz (x) = c - (clz (x & ~x)) where c is the mode precision minus 1 which should be faster than a loop. gcc/ChangeLog: PR tree-optimization/110490 * tree-scalar-evolution.cc (expression_expensive_p): Also consider mode widening for popcount, clz, and ctz. Diff: --- gcc/tree-scalar-evolution.cc | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) diff --git a/gcc/tree-scalar-evolution.cc b/gcc/tree-scalar-evolution.cc index b0a5e09a77c..622c7246c1b 100644 --- a/gcc/tree-scalar-evolution.cc +++ b/gcc/tree-scalar-evolution.cc @@ -3458,6 +3458,28 @@ bitcount_call: && (optab_handler (optab, word_mode) != CODE_FOR_nothing)) break; + /* If popcount is available for a wider mode, we emulate the + operation for a narrow mode by first zero-extending the value + and then computing popcount in the wider mode. Analogue for + ctz. For clz we do the same except that we additionally have + to subtract the difference of the mode precisions from the + result. */ + if (is_a <scalar_int_mode> (mode, &int_mode)) + { + machine_mode wider_mode_iter; + FOR_EACH_WIDER_MODE (wider_mode_iter, mode) + if (optab_handler (optab, wider_mode_iter) + != CODE_FOR_nothing) + goto check_call_args; + /* Operation ctz may be emulated via clz in expand_ctz. */ + if (optab == ctz_optab) + { + FOR_EACH_WIDER_MODE_FROM (wider_mode_iter, mode) + if (optab_handler (clz_optab, wider_mode_iter) + != CODE_FOR_nothing) + goto check_call_args; + } + } return true; } break; @@ -3469,6 +3491,7 @@ bitcount_call: break; } +check_call_args: FOR_EACH_CALL_EXPR_ARG (arg, iter, expr) if (expression_expensive_p (arg, cond_overflow_p, cache, op_cost)) return true;