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author | Jakub Jelinek <jakub@redhat.com> | 2022-03-17 09:23:45 +0100 |
---|---|---|
committer | Jakub Jelinek <jakub@redhat.com> | 2022-03-17 09:23:45 +0100 |
commit | 7276a18aba41eed65c0cf535ae029e0ceeca6c77 (patch) | |
tree | a163c864d333b053dc347b653181f82a39c25520 | |
parent | c43cb355f25dd22133d15819bd6ec03d3d3939fd (diff) | |
download | gcc-7276a18aba41eed65c0cf535ae029e0ceeca6c77.zip gcc-7276a18aba41eed65c0cf535ae029e0ceeca6c77.tar.gz gcc-7276a18aba41eed65c0cf535ae029e0ceeca6c77.tar.bz2 |
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 <D.2517>; else goto <D.2518>;
<D.2517>:
A::~A (&D.2499.e);
goto <D.2519>;
<D.2518>:
<D.2519>:
}
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)>
<L2>:
D.2499 ={v} {CLOBBER(eol)};
D.2498 ={v} {CLOBBER(eol)};
if (_3 != 0)
goto <bb 11>; [INV]
else
goto <bb 15>; [INV]
<bb 11> :
_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 <D.2517>; else goto <D.2518>;
<D.2517>:
A::~A (&D.2499.e);
goto <D.2519>;
<D.2518>:
<D.2519>:
}
}
finally
{
D.2499 = {CLOBBER(eol)};
}
2022-03-17 Jakub Jelinek <jakub@redhat.com>
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.
-rw-r--r-- | gcc/gimplify.cc | 34 | ||||
-rw-r--r-- | gcc/testsuite/g++.dg/opt/pr103984.C | 31 |
2 files changed, 47 insertions, 18 deletions
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) }); +} |