From 7276a18aba41eed65c0cf535ae029e0ceeca6c77 Mon Sep 17 00:00:00 2001 From: Jakub Jelinek Date: Thu, 17 Mar 2022 09:23:45 +0100 Subject: [PATCH] gimplify: Emit clobbers for TARGET_EXPR_SLOT vars later [PR103984] As mentioned in the PR, we emit a bogus uninitialized warning but easily could emit wrong-code for it or similar testcases too. The bug is that we emit clobber for a TARGET_EXPR_SLOT too early: D.2499.e = B::qux (&h); [return slot optimization] D.2516 = 1; try { B::B (&D.2498, &h); try { _2 = baz (&D.2498); D.2499.f = _2; D.2516 = 0; try { try { bar (&D.2499); } finally { C::~C (&D.2499); } } finally { D.2499 = {CLOBBER(eol)}; } } finally { D.2498 = {CLOBBER(eol)}; } } catch { if (D.2516 != 0) goto ; else goto ; : A::~A (&D.2499.e); goto ; : : } The CLOBBER for D.2499 is essentially only emitted on the non-exceptional path, if B::B or baz throws, then there is no CLOBBER for it but there is a conditional destructor A::~A (&D.2499.e). Now, ehcleanup1 sink_clobbers optimization assumes that clobbers in the EH cases are emitted after last use and so sinks the D.2499 = {CLOBBER(eol)}; later, so we then have # _3 = PHI <1(3), 0(9)> : D.2499 ={v} {CLOBBER(eol)}; D.2498 ={v} {CLOBBER(eol)}; if (_3 != 0) goto ; [INV] else goto ; [INV] : _35 = D.2499.a; if (&D.2499.b != _35) where that _35 = D.2499.a comes from inline expansion of the A::~A dtor, and that is a load from a clobbered memory. Now, what the gimplifier sees in this case is a CLEANUP_POINT_EXPR with somewhere inside of it a TARGET_EXPR for D.2499 (with the C::~C (&D.2499) cleanup) which in its TARGET_EXPR_INITIAL has another TARGET_EXPR for D.2516 bool flag which has CLEANUP_EH_ONLY which performs that conditional A::~A (&D.2499.e) call. The following patch ensures that CLOBBERs (and asan poisoning) are emitted after even those gimple_push_cleanup pushed cleanups from within the TARGET_EXPR_INITIAL gimplification (i.e. the last point where the slot could be in theory used). In my first version of the patch I've done it by just moving the /* Add a clobber for the temporary going out of scope, like gimplify_bind_expr. */ if (gimplify_ctxp->in_cleanup_point_expr && needs_to_live_in_memory (temp)) { ... } block earlier in gimplify_target_expr, but that regressed a couple of tests where temp is marked TREE_ADDRESSABLE only during (well, very early during that) the gimplification of TARGET_EXPR_INITIAL, so we didn't emit e.g. on pr80032.C or stack2.C tests any clobbers for the slots and thus stack slot reuse wasn't performed. So that we don't regress those tests, this patch gimplifies TARGET_EXPR_INITIAL as before, but doesn't emit it directly into pre_p, emits it into a temporary sequence. Then emits the CLOBBER cleanup into pre_p, then asan poisoning if needed, then appends the TARGET_EXPR_INITIAL temporary sequence and finally adds TARGET_EXPR_CLEANUP gimple_push_cleanup. The earlier a GIMPLE_WCE appears in the sequence, the outer try/finally or try/catch it is. So, with this patch the part of the testcase in gimple dump cited above looks instead like: try { D.2499.e = B::qux (&h); [return slot optimization] D.2516 = 1; try { try { B::B (&D.2498, &h); _2 = baz (&D.2498); D.2499.f = _2; D.2516 = 0; try { bar (&D.2499); } finally { C::~C (&D.2499); } } finally { D.2498 = {CLOBBER(eol)}; } } catch { if (D.2516 != 0) goto ; else goto ; : A::~A (&D.2499.e); goto ; : : } } finally { D.2499 = {CLOBBER(eol)}; } 2022-03-17 Jakub Jelinek PR middle-end/103984 * gimplify.cc (gimplify_target_expr): Gimplify type sizes and TARGET_EXPR_INITIAL into a temporary sequence, then push clobbers and asan unpoisioning, then append the temporary sequence and finally the TARGET_EXPR_CLEANUP clobbers. * g++.dg/opt/pr103984.C: New test. --- gcc/gimplify.cc | 34 ++++++++++++++++------------------ gcc/testsuite/g++.dg/opt/pr103984.C | 31 +++++++++++++++++++++++++++++++ 2 files changed, 47 insertions(+), 18 deletions(-) create mode 100644 gcc/testsuite/g++.dg/opt/pr103984.C diff --git a/gcc/gimplify.cc b/gcc/gimplify.cc index c6ba0c3..139a0de 100644 --- a/gcc/gimplify.cc +++ b/gcc/gimplify.cc @@ -6997,17 +6997,17 @@ gimplify_target_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p) if (init) { - tree cleanup = NULL_TREE; + gimple_seq init_pre_p = NULL; /* TARGET_EXPR temps aren't part of the enclosing block, so add it to the temps list. Handle also variable length TARGET_EXPRs. */ if (!poly_int_tree_p (DECL_SIZE (temp))) { if (!TYPE_SIZES_GIMPLIFIED (TREE_TYPE (temp))) - gimplify_type_sizes (TREE_TYPE (temp), pre_p); + gimplify_type_sizes (TREE_TYPE (temp), &init_pre_p); /* FIXME: this is correct only when the size of the type does not depend on expressions evaluated in init. */ - gimplify_vla_decl (temp, pre_p); + gimplify_vla_decl (temp, &init_pre_p); } else { @@ -7022,12 +7022,14 @@ gimplify_target_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p) /* If TARGET_EXPR_INITIAL is void, then the mere evaluation of the expression is supposed to initialize the slot. */ if (VOID_TYPE_P (TREE_TYPE (init))) - ret = gimplify_expr (&init, pre_p, post_p, is_gimple_stmt, fb_none); + ret = gimplify_expr (&init, &init_pre_p, post_p, is_gimple_stmt, + fb_none); else { tree init_expr = build2 (INIT_EXPR, void_type_node, temp, init); init = init_expr; - ret = gimplify_expr (&init, pre_p, post_p, is_gimple_stmt, fb_none); + ret = gimplify_expr (&init, &init_pre_p, post_p, is_gimple_stmt, + fb_none); init = NULL; ggc_free (init_expr); } @@ -7037,18 +7039,9 @@ gimplify_target_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p) TARGET_EXPR_INITIAL (targ) = NULL_TREE; return GS_ERROR; } - if (init) - gimplify_and_add (init, pre_p); - /* If needed, push the cleanup for the temp. */ - if (TARGET_EXPR_CLEANUP (targ)) - { - if (CLEANUP_EH_ONLY (targ)) - gimple_push_cleanup (temp, TARGET_EXPR_CLEANUP (targ), - CLEANUP_EH_ONLY (targ), pre_p); - else - cleanup = TARGET_EXPR_CLEANUP (targ); - } + if (init) + gimplify_and_add (init, &init_pre_p); /* Add a clobber for the temporary going out of scope, like gimplify_bind_expr. */ @@ -7079,8 +7072,13 @@ gimplify_target_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p) } } } - if (cleanup) - gimple_push_cleanup (temp, cleanup, false, pre_p); + + gimple_seq_add_seq (pre_p, init_pre_p); + + /* If needed, push the cleanup for the temp. */ + if (TARGET_EXPR_CLEANUP (targ)) + gimple_push_cleanup (temp, TARGET_EXPR_CLEANUP (targ), + CLEANUP_EH_ONLY (targ), pre_p); /* Only expand this once. */ TREE_OPERAND (targ, 3) = init; diff --git a/gcc/testsuite/g++.dg/opt/pr103984.C b/gcc/testsuite/g++.dg/opt/pr103984.C new file mode 100644 index 0000000..b9cb943 --- /dev/null +++ b/gcc/testsuite/g++.dg/opt/pr103984.C @@ -0,0 +1,31 @@ +// PR middle-end/103984 +// { dg-do compile { target c++11 } } +// { dg-options "-O2 -Wuninitialized" } + +struct A { + char *a; + char b[4]; + A (); + A (const A &); + A (const char *); + A (const char *, const char *); + [[gnu::always_inline]] ~A () { if (a != b) delete a; } +}; +struct B { + const char *c = nullptr; + const char *d = nullptr; + A qux () const { return A (c, d); } + B (const char *x) : c(x), d(x) { d += __builtin_strlen (x); } + B (const B &x) { c = x.c; d = x.d; } +}; +struct C { A e; int f; }; +extern int baz (B); +void bar (C &&); + +void +foo (char **x) +{ + const A g ("foo"); + const B h = x[0]; + bar (C { h.qux (), baz (h) }); +} -- 2.7.4