From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 2140) id 4839038618AF; Sat, 10 Jul 2021 09:43:55 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 4839038618AF Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit From: Alexandre Oliva To: gcc-cvs@gcc.gnu.org Subject: [gcc(refs/users/aoliva/heads/testme)] avoid early reference to debug-only symbol X-Act-Checkin: gcc X-Git-Author: Alexandre Oliva X-Git-Refname: refs/users/aoliva/heads/testme X-Git-Oldrev: e15b2c5da846bf082957c4240ff386b8f8154728 X-Git-Newrev: 7a0d3299c7af17c36d533ed2e476c110bcfbd424 Message-Id: <20210710094355.4839038618AF@sourceware.org> Date: Sat, 10 Jul 2021 09:43:55 +0000 (GMT) X-BeenThere: gcc-cvs@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-cvs mailing list List-Unsubscribe: , List-Archive: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 10 Jul 2021 09:43:55 -0000 https://gcc.gnu.org/g:7a0d3299c7af17c36d533ed2e476c110bcfbd424 commit 7a0d3299c7af17c36d533ed2e476c110bcfbd424 Author: Alexandre Oliva Date: Fri Jul 9 19:54:46 2021 -0300 avoid early reference to debug-only symbol If some IPA pass replaces the only reference to a constant non-public non-automatic variable with its initializer, namely the address of another such variable, the former becomes unreferenced and it's discarded by symbol_table::remove_unreachable_nodes. It calls debug_hooks->late_global_decl while at that, and this expands the initializer, which assigs RTL to the latter variable and forces it to be retained by remove_unreferenced_decls, and eventually be output despite not being referenced. Without debug information, it's not output. This has caused a bootstrap-debug compare failure in libdecnumber/decContext.o, while developing a transformation that ends up enabling the above substitution in constprop. This patch makes reference_to_unused slightly more conservative about such variables at the end of IPA passes, falling back onto expand_debug_expr for expressions referencing symbols that might or might not be output, avoiding the loss of debug information when the symbol is output, while avoiding a symbol output only because of debug info. Diff: --- gcc/cfgexpand.c | 12 +++++++++--- gcc/dwarf2out.c | 15 +++++++++++++-- gcc/expr.h | 2 ++ 3 files changed, 24 insertions(+), 5 deletions(-) diff --git a/gcc/cfgexpand.c b/gcc/cfgexpand.c index 3edd53c37dc..b731a559823 100644 --- a/gcc/cfgexpand.c +++ b/gcc/cfgexpand.c @@ -91,8 +91,6 @@ struct ssaexpand SA; of comminucating the profile info to the builtin expanders. */ gimple *currently_expanding_gimple_stmt; -static rtx expand_debug_expr (tree); - static bool defer_stack_allocation (tree, bool); static void record_alignment_for_reg_var (unsigned int); @@ -4413,7 +4411,7 @@ expand_debug_parm_decl (tree decl) /* Return an RTX equivalent to the value of the tree expression EXP. */ -static rtx +rtx expand_debug_expr (tree exp) { rtx op0 = NULL_RTX, op1 = NULL_RTX, op2 = NULL_RTX; @@ -5285,6 +5283,14 @@ expand_debug_expr (tree exp) else goto flag_unsupported; + case COMPOUND_LITERAL_EXPR: + exp = COMPOUND_LITERAL_EXPR_DECL_EXPR (exp); + /* DECL_EXPR is a tcc_statement, which expand_debug_expr does + not expect, so instead of recursing we take care of it right + away. */ + exp = DECL_EXPR_DECL (exp); + return expand_debug_expr (exp); + case CALL_EXPR: /* ??? Maybe handle some builtins? */ return NULL; diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c index 82783c4968b..bb7e2b8dc4e 100644 --- a/gcc/dwarf2out.c +++ b/gcc/dwarf2out.c @@ -20170,7 +20170,8 @@ add_const_value_attribute (dw_die_ref die, rtx rtl) if (dwarf_version >= 4 || !dwarf_strict) { dw_loc_descr_ref loc_result; - resolve_one_addr (&rtl); + if (!resolve_one_addr (&rtl)) + return false; rtl_addr: loc_result = new_addr_loc_descr (rtl, dtprel_false); add_loc_descr (&loc_result, new_loc_descr (DW_OP_stack_value, 0, 0)); @@ -20255,6 +20256,12 @@ reference_to_unused (tree * tp, int * walk_subtrees, varpool_node *node = varpool_node::get (*tp); if (!node || !node->definition) return *tp; + /* If it's local, it might still be optimized out, unless we've + already committed to outputting it by assigning RTL to it. */ + if (! TREE_PUBLIC (*tp) && ! TREE_ASM_WRITTEN (*tp) + && symtab->state <= IPA_SSA_AFTER_INLINING + && ! DECL_RTL_SET_P (*tp)) + return *tp; } else if (TREE_CODE (*tp) == FUNCTION_DECL && (!DECL_EXTERNAL (*tp) || DECL_DECLARED_INLINE_P (*tp))) @@ -20279,6 +20286,7 @@ static rtx rtl_for_decl_init (tree init, tree type) { rtx rtl = NULL_RTX; + bool valid_p = false; STRIP_NOPS (init); @@ -20322,7 +20330,7 @@ rtl_for_decl_init (tree init, tree type) /* If the initializer is something that we know will expand into an immediate RTL constant, expand it now. We must be careful not to reference variables which won't be output. */ - else if (initializer_constant_valid_p (init, type) + else if ((valid_p = initializer_constant_valid_p (init, type)) && ! walk_tree (&init, reference_to_unused, NULL, NULL)) { /* Convert vector CONSTRUCTOR initializers to VECTOR_CST if @@ -20367,6 +20375,9 @@ rtl_for_decl_init (tree init, tree type) /* If expand_expr returns a MEM, it wasn't immediate. */ gcc_assert (!rtl || !MEM_P (rtl)); } + else if (valid_p) + /* Perhaps we could just use this and skip all of the above? */ + rtl = expand_debug_expr (init); return rtl; } diff --git a/gcc/expr.h b/gcc/expr.h index a4f44265759..7b060462020 100644 --- a/gcc/expr.h +++ b/gcc/expr.h @@ -307,6 +307,8 @@ expand_normal (tree exp) return expand_expr_real (exp, NULL_RTX, VOIDmode, EXPAND_NORMAL, NULL, false); } +/* This one is defined in cfgexpand.c. */ +extern rtx expand_debug_expr (tree); /* Return STRING_CST and set offset, size and decl, if the first argument corresponds to a string constant. */