https://gcc.gnu.org/g:a729b1227bc8c84cd91a3b8c9c9d11bc43d415de
commit r13-8482-ga729b1227bc8c84cd91a3b8c9c9d11bc43d415de Author: Richard Biener <rguent...@suse.de> Date: Mon Mar 4 10:38:31 2024 +0100 tree-optimization/114203 - wrong CLZ niter computation For precision less than int we apply the adjustment to make it defined at zero after the adjustment to make it compute CLZ rather than CTZ. That's wrong. PR tree-optimization/114203 * tree-ssa-loop-niter.cc (build_cltz_expr): Apply CTZ->CLZ adjustment before making the result defined at zero. * gcc.dg/torture/pr114203.c: New testcase. (cherry picked from commit cde50296a19b109909089b91d532d2c8455f5f10) Diff: --- gcc/testsuite/gcc.dg/torture/pr114203.c | 21 +++++++++++++++++++++ gcc/tree-ssa-loop-niter.cc | 7 +++---- 2 files changed, 24 insertions(+), 4 deletions(-) diff --git a/gcc/testsuite/gcc.dg/torture/pr114203.c b/gcc/testsuite/gcc.dg/torture/pr114203.c new file mode 100644 index 00000000000..0ef6279942a --- /dev/null +++ b/gcc/testsuite/gcc.dg/torture/pr114203.c @@ -0,0 +1,21 @@ +/* { dg-do run } */ + +int __attribute__((noipa)) +foo (unsigned char b) +{ + int c = 0; + + while (b) { + b >>= 1; + c++; + } + + return c; +} + +int main() +{ + if (foo(0) != 0) + __builtin_abort (); + return 0; +} diff --git a/gcc/tree-ssa-loop-niter.cc b/gcc/tree-ssa-loop-niter.cc index dc4c7a418f6..0ffe4b8465d 100644 --- a/gcc/tree-ssa-loop-niter.cc +++ b/gcc/tree-ssa-loop-niter.cc @@ -2299,6 +2299,9 @@ build_cltz_expr (tree src, bool leading, bool define_at_zero) src = fold_convert (unsigned_type_node, src); call = build_call_expr (fn, 1, src); + if (leading && prec < i_prec) + call = fold_build2 (MINUS_EXPR, integer_type_node, call, + build_int_cst (integer_type_node, i_prec - prec)); if (define_at_zero) { tree is_zero = fold_build2 (NE_EXPR, boolean_type_node, src, @@ -2306,10 +2309,6 @@ build_cltz_expr (tree src, bool leading, bool define_at_zero) call = fold_build3 (COND_EXPR, integer_type_node, is_zero, call, build_int_cst (integer_type_node, prec)); } - - if (leading && prec < i_prec) - call = fold_build2 (MINUS_EXPR, integer_type_node, call, - build_int_cst (integer_type_node, i_prec - prec)); } return call;