https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103984
--- Comment #18 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:7276a18aba41eed65c0cf535ae029e0ceeca6c77 commit r12-7686-g7276a18aba41eed65c0cf535ae029e0ceeca6c77 Author: Jakub Jelinek <ja...@redhat.com> Date: Thu Mar 17 09:23:45 2022 +0100 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 <ja...@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.
