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From: Richard Biener <rguenth@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org Subject: [gcc r14-9293] tree-optimization/114203 - wrong CLZ niter computation Date: Mon, 4 Mar 2024 10:45:28 +0000 (GMT) [thread overview] Message-ID: <20240304104528.85B683858C32@sourceware.org> (raw) https://gcc.gnu.org/g:cde50296a19b109909089b91d532d2c8455f5f10 commit r14-9293-gcde50296a19b109909089b91d532d2c8455f5f10 Author: Richard Biener <rguenther@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. 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 038e4331661..c6d010f6d89 100644 --- a/gcc/tree-ssa-loop-niter.cc +++ b/gcc/tree-ssa-loop-niter.cc @@ -2288,6 +2288,9 @@ 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, @@ -2295,10 +2298,6 @@ 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;
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