From 70e72c3a11315fb6a228b7f58d027c2e1fbb9940 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 d94e3b962db4..38913b06717c 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