https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100394
--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Richard Biener <rgue...@gcc.gnu.org>: https://gcc.gnu.org/g:8ebf6b99952ada09bf9ea0144dcd1d46363b0464 commit r12-475-g8ebf6b99952ada09bf9ea0144dcd1d46363b0464 Author: Richard Biener <rguent...@suse.de> Date: Mon May 3 15:11:28 2021 +0200 middle-end/100394 - avoid DSE/DCE of pure call that throws There is -fdelete-dead-exceptions now and we're tracking nothrow and const/pure bits separately and I do remember that const or pure does _not_ imply nothrow. Now, in the light of the PR100382 fix which added a stmt_unremovable_because_of_non_call_eh_p guard to DSEs "DCE" I wondered how -fdelete-dead-exceptions applies to calls and whether stmt_unremovable_because_of_non_call_eh_p doing return (fun->can_throw_non_call_exceptions && !fun->can_delete_dead_exceptions && stmt_could_throw_p (fun, stmt)); really should conditionalize itself on fun->can_throw_non_call_exceptions. In fact DCE happily elides pure function calls that throw without a LHS (probably a consistency bug). The following testcase shows this: int x, y; int __attribute__((pure,noinline)) foo () { if (x) throw 1; return y; } int main() { int a[2]; x = 1; try { int res = foo (); a[0] = res; } catch (...) { return 0; } return 1; } note that if you wrap foo () into another noinline wrap_foo () { foo (); return 1; } function then we need to make sure to not DCE this call either even though it only throws externally. 2021-05-03 Richard Biener <rguent...@suse.de> PR middle-end/100394 * calls.c (expand_call): Preserve possibly throwing calls. * cfgexpand.c (expand_call_stmt): When a call can throw signal RTL expansion there are side-effects. * tree-ssa-dce.c (mark_stmt_if_obviously_necessary): Simplify, mark all possibly throwing stmts necessary unless we can elide dead EH. * tree-ssa-dse.c (pass_dse::execute): Preserve exceptions unless -fdelete-dead-exceptions. * tree.h (DECL_PURE_P): Add note about exceptions. * g++.dg/torture/pr100382.C: New testcase.
