https://gcc.gnu.org/g:7dd39924c9a696a627522e897ed8c7bd454872bd
commit r16-5911-g7dd39924c9a696a627522e897ed8c7bd454872bd Author: Richard Biener <[email protected]> Date: Thu Jul 10 15:19:30 2025 +0200 tree-optimization/120939 - remove uninitialized use of LOOP_VINFO_COST_MODEL_THRESHOLD The following removes an optimization that wrongly triggers right now because it accesses LOOP_VINFO_COST_MODEL_THRESHOLD which might not be computed yet and uses guessed likely max stmt executions. It also refactors the code to make the default conservative. PR tree-optimization/120939 * tree-vect-loop.cc (vect_need_peeling_or_partial_vectors_p): Remove eliding an epilogue based on not computed LOOP_VINFO_COST_MODEL_THRESHOLD and estimated max stmt executions. * gcc.dg/torture/pr113026-1.c: Skip when -ftracer. Diff: --- gcc/testsuite/gcc.dg/torture/pr113026-1.c | 4 ++- gcc/tree-vect-loop.cc | 45 +++++++++++-------------------- 2 files changed, 18 insertions(+), 31 deletions(-) diff --git a/gcc/testsuite/gcc.dg/torture/pr113026-1.c b/gcc/testsuite/gcc.dg/torture/pr113026-1.c index 56dfef3b36c4..37b5281d547f 100644 --- a/gcc/testsuite/gcc.dg/torture/pr113026-1.c +++ b/gcc/testsuite/gcc.dg/torture/pr113026-1.c @@ -1,4 +1,6 @@ -/* { dg-do compile } */ +/* { dg-do compile } */ +/* When tracing the vector epilog we diagnose an unreachable access. */ +/* { dg-skip-if "" { *-*-* } { "-ftracer" } { "" } } */ /* { dg-additional-options "-Wall" } */ char dst[16]; diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc index 3ac264f0ce32..82121ca21ba4 100644 --- a/gcc/tree-vect-loop.cc +++ b/gcc/tree-vect-loop.cc @@ -941,13 +941,6 @@ static bool vect_need_peeling_or_partial_vectors_p (loop_vec_info loop_vinfo) { unsigned HOST_WIDE_INT const_vf; - HOST_WIDE_INT max_niter - = likely_max_stmt_executions_int (LOOP_VINFO_LOOP (loop_vinfo)); - - unsigned th = LOOP_VINFO_COST_MODEL_THRESHOLD (loop_vinfo); - if (!th && LOOP_VINFO_ORIG_LOOP_INFO (loop_vinfo)) - th = LOOP_VINFO_COST_MODEL_THRESHOLD (LOOP_VINFO_ORIG_LOOP_INFO - (loop_vinfo)); loop_vec_info main_loop_vinfo = (LOOP_VINFO_EPILOGUE_P (loop_vinfo) @@ -961,31 +954,23 @@ vect_need_peeling_or_partial_vectors_p (loop_vec_info loop_vinfo) = LOOP_VINFO_PEELING_FOR_ALIGNMENT (main_loop_vinfo); if (LOOP_VINFO_PEELING_FOR_GAPS (loop_vinfo)) peel_niter += 1; - if (!multiple_p (LOOP_VINFO_INT_NITERS (loop_vinfo) - peel_niter, - LOOP_VINFO_VECT_FACTOR (loop_vinfo))) - return true; + return !multiple_p (LOOP_VINFO_INT_NITERS (loop_vinfo) - peel_niter, + LOOP_VINFO_VECT_FACTOR (loop_vinfo)); } - else if (LOOP_VINFO_PEELING_FOR_ALIGNMENT (main_loop_vinfo) - /* ??? When peeling for gaps but not alignment, we could - try to check whether the (variable) niters is known to be - VF * N + 1. That's something of a niche case though. */ - || LOOP_VINFO_PEELING_FOR_GAPS (loop_vinfo) - || !LOOP_VINFO_VECT_FACTOR (loop_vinfo).is_constant (&const_vf) - || ((tree_ctz (LOOP_VINFO_NITERS (loop_vinfo)) - < (unsigned) exact_log2 (const_vf)) - /* In case of versioning, check if the maximum number of - iterations is greater than th. If they are identical, - the epilogue is unnecessary. */ - && (!LOOP_REQUIRES_VERSIONING (loop_vinfo) - || ((unsigned HOST_WIDE_INT) max_niter - /* We'd like to use LOOP_VINFO_VERSIONING_THRESHOLD - but that's only computed later based on our result. - The following is the most conservative approximation. */ - > (std::max ((unsigned HOST_WIDE_INT) th, - const_vf) / const_vf) * const_vf)))) - return true; - return false; + if (!LOOP_VINFO_PEELING_FOR_ALIGNMENT (main_loop_vinfo) + && !LOOP_VINFO_PEELING_FOR_GAPS (loop_vinfo) + && LOOP_VINFO_VECT_FACTOR (loop_vinfo).is_constant (&const_vf)) + { + /* When the number of iterations is a multiple of the vectorization + factor and we are not doing prologue or forced epilogue peeling + the epilogue isn't necessary. */ + if (tree_ctz (LOOP_VINFO_NITERS (loop_vinfo)) + >= (unsigned) exact_log2 (const_vf)) + return false; + } + + return true; } /* Each statement in LOOP_VINFO can be masked where necessary. Check
