From e93809f62363ba4b233858005aef652fb550e896 Mon Sep 17 00:00:00 2001 From: Jan Hubicka Date: Sun, 12 Dec 2021 11:38:13 +0100 Subject: [PATCH] Terminate BB analysis on NULL memory access in ipa-pure-const and ipa-modref As discussed in the PR, we miss some optimization becuase gimple-ssa-isolate-paths turns NULL memory accesses to volatile and adds __builtin_trap after them. This is seen as a side-effect by IPA analysis and additionally the (fully unreachable) builtin_trap is believed to load all global memory. I think we should think of less intrusive gimple representation of this, but it is also easy enough to special case that in IPA analysers as done in this patch. This is a win even if we improve the representation since gimple-ssa-isolate-paths is run late and this way we improve optimization early. This affects 1623 functions during cc1plus link. Bootstrapped/regtested x86_64-linux, comitted. gcc/ChangeLog: 2021-12-12 Jan Hubicka PR ipa/103665 * ipa-modref.c (modref_access_analysis::analyze): Terminate BB analysis on NULL memory access. * ipa-pure-const.c (analyze_function): Likewise. --- gcc/ipa-modref.c | 13 +++++++++++++ gcc/ipa-pure-const.c | 22 ++++++++++++++++++++++ 2 files changed, 35 insertions(+) diff --git a/gcc/ipa-modref.c b/gcc/ipa-modref.c index 55fa873e1f05..2c89c63baf67 100644 --- a/gcc/ipa-modref.c +++ b/gcc/ipa-modref.c @@ -1750,6 +1750,19 @@ modref_access_analysis::analyze () for (si = gsi_start_nondebug_after_labels_bb (bb); !gsi_end_p (si); gsi_next_nondebug (&si)) { + /* NULL memory accesses terminates BB. These accesses are known + to trip undefined behaviour. gimple-ssa-isolate-paths turns them + to volatile accesses and adds builtin_trap call which would + confuse us otherwise. */ + if (infer_nonnull_range_by_dereference (gsi_stmt (si), + null_pointer_node)) + { + if (dump_file) + fprintf (dump_file, " - NULL memory access; terminating BB\n"); + if (flag_non_call_exceptions) + set_side_effects (); + break; + } analyze_stmt (gsi_stmt (si), always_executed); /* Avoid doing useles work. */ diff --git a/gcc/ipa-pure-const.c b/gcc/ipa-pure-const.c index fea8b08c4eb7..25503f360e64 100644 --- a/gcc/ipa-pure-const.c +++ b/gcc/ipa-pure-const.c @@ -1097,6 +1097,28 @@ analyze_function (struct cgraph_node *fn, bool ipa) !gsi_end_p (gsi); gsi_next (&gsi)) { + /* NULL memory accesses terminates BB. These accesses are known + to trip undefined behaviour. gimple-ssa-isolate-paths turns them + to volatile accesses and adds builtin_trap call which would + confuse us otherwise. */ + if (infer_nonnull_range_by_dereference (gsi_stmt (gsi), + null_pointer_node)) + { + if (dump_file) + fprintf (dump_file, " NULL memory access; terminating BB%s\n", + flag_non_call_exceptions ? "; looping" : ""); + if (flag_non_call_exceptions) + { + l->looping = true; + if (stmt_can_throw_external (cfun, gsi_stmt (gsi))) + { + if (dump_file) + fprintf (dump_file, " can throw externally\n"); + l->can_throw = true; + } + } + break; + } check_stmt (&gsi, l, ipa); if (l->pure_const_state == IPA_NEITHER && l->looping -- 2.47.2