https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86638
--- Comment #5 from Eric Gallager <egallager at gcc dot gnu.org> --- (In reply to rsand...@gcc.gnu.org from comment #4) > Author: rsandifo > Date: Mon Jul 29 08:52:56 2019 > New Revision: 273872 > > URL: https://gcc.gnu.org/viewcvs?rev=273872&root=gcc&view=rev > Log: > Prevent tree-ssa-dce.c from deleting stores at -Og > > DCE tries to delete dead stores to local data and also tries to insert > debug binds for simple cases: > > /* If this is a store into a variable that is being optimized away, > add a debug bind stmt if possible. */ > if (MAY_HAVE_DEBUG_BIND_STMTS > && gimple_assign_single_p (stmt) > && is_gimple_val (gimple_assign_rhs1 (stmt))) > { > tree lhs = gimple_assign_lhs (stmt); > if ((VAR_P (lhs) || TREE_CODE (lhs) == PARM_DECL) > && !DECL_IGNORED_P (lhs) > && is_gimple_reg_type (TREE_TYPE (lhs)) > && !is_global_var (lhs) > && !DECL_HAS_VALUE_EXPR_P (lhs)) > { > tree rhs = gimple_assign_rhs1 (stmt); > gdebug *note > = gimple_build_debug_bind (lhs, unshare_expr (rhs), stmt); > gsi_insert_after (i, note, GSI_SAME_STMT); > } > } > > But this doesn't help for things like "print *ptr" when ptr points > to the local variable (tests Og-dce-1.c and Og-dce-2.c). It can > also introduce wrong debug info for earlier references (second test > in Og-dce-3.c) or make earlier references unavailable (first test > in Og-dce-3.c). > > So for -Og I think it'd be better not to delete any stmts with > vdefs for now. This also means that we can avoid the potentially > expensive vop walks (which already have a cut-off, but still). > > The patch also fixes the Og failures in gcc.dg/guality/pr54970.c > (PR 86638). > So can this be closed now then? > 2019-07-29 Richard Sandiford <richard.sandif...@arm.com> > > gcc/ > PR debug/86638 > * tree-ssa-dce.c (keep_all_vdefs_p): New function. > (mark_stmt_if_obviously_necessary): Mark all stmts with vdefs as > necessary if keep_all_vdefs_p is true. > (mark_aliased_reaching_defs_necessary): Add a gcc_checking_assert > that keep_all_vdefs_p is false. > (mark_all_reaching_defs_necessary): Likewise. > (propagate_necessity): Skip the vuse scan if keep_all_vdefs_p is true. > > gcc/testsuite/ > * c-c++-common/guality/Og-dce-1.c: New test. > * c-c++-common/guality/Og-dce-2.c: Likewise. > * c-c++-common/guality/Og-dce-3.c: Likewise. > > Added: > trunk/gcc/testsuite/c-c++-common/guality/Og-dce-1.c > trunk/gcc/testsuite/c-c++-common/guality/Og-dce-2.c > trunk/gcc/testsuite/c-c++-common/guality/Og-dce-3.c > Modified: > trunk/gcc/ChangeLog > trunk/gcc/testsuite/ChangeLog > trunk/gcc/tree-ssa-dce.c
