From e53fbb17839723ea1697fcbaf76b1c092675eaaf Mon Sep 17 00:00:00 2001 From: Aldy Hernandez Date: Wed, 20 Oct 2021 18:52:45 +0200 Subject: [PATCH] Avoid threading circular paths. The backward threader keeps a hash of visited blocks to avoid crossing the same block twice. Interestingly, we haven't been checking it for the final block out of the path. This may be inherited from the old code, as it was simple enough that it didn't matter. With the upcoming changes enabling the fully resolving threader, it gets tripped often enough to cause wrong code to be generated. Tested on x86-64 Linux. gcc/ChangeLog: * tree-ssa-threadbackward.c (back_threader::maybe_register_path): Avoid threading circular paths. --- gcc/tree-ssa-threadbackward.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/gcc/tree-ssa-threadbackward.c b/gcc/tree-ssa-threadbackward.c index a6b9893abbdf..d9ce056b06ce 100644 --- a/gcc/tree-ssa-threadbackward.c +++ b/gcc/tree-ssa-threadbackward.c @@ -140,6 +140,10 @@ back_threader::maybe_register_path () if (taken_edge && taken_edge != UNREACHABLE_EDGE) { + // Avoid circular paths. + if (m_visited_bbs.contains (taken_edge->dest)) + return UNREACHABLE_EDGE; + bool irreducible = false; bool profitable = m_profit.profitable_path_p (m_path, m_name, taken_edge, &irreducible); -- 2.47.2