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.
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@ -6997,17 +6997,17 @@ gimplify_target_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p)
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if (init)
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{
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tree cleanup = NULL_TREE;
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gimple_seq init_pre_p = NULL;
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/* TARGET_EXPR temps aren't part of the enclosing block, so add it
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to the temps list. Handle also variable length TARGET_EXPRs. */
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if (!poly_int_tree_p (DECL_SIZE (temp)))
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{
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if (!TYPE_SIZES_GIMPLIFIED (TREE_TYPE (temp)))
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gimplify_type_sizes (TREE_TYPE (temp), pre_p);
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gimplify_type_sizes (TREE_TYPE (temp), &init_pre_p);
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/* FIXME: this is correct only when the size of the type does
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not depend on expressions evaluated in init. */
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gimplify_vla_decl (temp, pre_p);
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gimplify_vla_decl (temp, &init_pre_p);
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}
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else
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{
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@ -7022,12 +7022,14 @@ gimplify_target_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p)
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/* If TARGET_EXPR_INITIAL is void, then the mere evaluation of the
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expression is supposed to initialize the slot. */
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if (VOID_TYPE_P (TREE_TYPE (init)))
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ret = gimplify_expr (&init, pre_p, post_p, is_gimple_stmt, fb_none);
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ret = gimplify_expr (&init, &init_pre_p, post_p, is_gimple_stmt,
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fb_none);
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else
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{
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tree init_expr = build2 (INIT_EXPR, void_type_node, temp, init);
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init = init_expr;
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ret = gimplify_expr (&init, pre_p, post_p, is_gimple_stmt, fb_none);
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ret = gimplify_expr (&init, &init_pre_p, post_p, is_gimple_stmt,
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fb_none);
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init = NULL;
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ggc_free (init_expr);
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}
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@ -7037,18 +7039,9 @@ gimplify_target_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p)
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TARGET_EXPR_INITIAL (targ) = NULL_TREE;
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return GS_ERROR;
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}
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if (init)
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gimplify_and_add (init, pre_p);
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/* If needed, push the cleanup for the temp. */
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if (TARGET_EXPR_CLEANUP (targ))
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{
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if (CLEANUP_EH_ONLY (targ))
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gimple_push_cleanup (temp, TARGET_EXPR_CLEANUP (targ),
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CLEANUP_EH_ONLY (targ), pre_p);
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else
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cleanup = TARGET_EXPR_CLEANUP (targ);
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}
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if (init)
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gimplify_and_add (init, &init_pre_p);
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/* Add a clobber for the temporary going out of scope, like
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gimplify_bind_expr. */
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@ -7079,8 +7072,13 @@ gimplify_target_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p)
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}
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}
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}
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if (cleanup)
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gimple_push_cleanup (temp, cleanup, false, pre_p);
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gimple_seq_add_seq (pre_p, init_pre_p);
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/* If needed, push the cleanup for the temp. */
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if (TARGET_EXPR_CLEANUP (targ))
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gimple_push_cleanup (temp, TARGET_EXPR_CLEANUP (targ),
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CLEANUP_EH_ONLY (targ), pre_p);
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/* Only expand this once. */
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TREE_OPERAND (targ, 3) = init;
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@ -0,0 +1,31 @@
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// PR middle-end/103984
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// { dg-do compile { target c++11 } }
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// { dg-options "-O2 -Wuninitialized" }
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struct A {
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char *a;
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char b[4];
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A ();
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A (const A &);
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A (const char *);
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A (const char *, const char *);
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[[gnu::always_inline]] ~A () { if (a != b) delete a; }
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};
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struct B {
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const char *c = nullptr;
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const char *d = nullptr;
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A qux () const { return A (c, d); }
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B (const char *x) : c(x), d(x) { d += __builtin_strlen (x); }
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B (const B &x) { c = x.c; d = x.d; }
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};
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struct C { A e; int f; };
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extern int baz (B);
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void bar (C &&);
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void
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foo (char **x)
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{
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const A g ("foo");
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const B h = x[0];
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bar (C { h.qux (), baz (h) });
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}
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