From 650af77812fc55ffc7c45e271b45a9b13a62dfd3 Mon Sep 17 00:00:00 2001 From: Akim Demaille Date: Tue, 13 Jan 2015 13:53:02 +0100 Subject: [PATCH] reduce: don't complain about rules whose lhs is useless In the following grammar, the 'exp' nonterminal is trivially useless. So, of course, its rules are useless too. %% input: '0' | exp exp: exp '+' exp | exp '-' exp | '(' exp ')' Previously all the useless rules were reported, including those whose left-hand side is the 'exp' nonterminal: warning: 1 nonterminal useless in grammar [-Wother] warning: 4 rules useless in grammar [-Wother] 2.14-16: warning: nonterminal useless in grammar: exp [-Wother] input: '0' | exp ^^^ 2.14-16: warning: rule useless in grammar [-Wother] input: '0' | exp ^^^ ! 3.6-16: warning: rule useless in grammar [-Wother] ! exp: exp '+' exp | exp '-' exp | '(' exp ')' ! ^^^^^^^^^^^ ! 3.20-30: warning: rule useless in grammar [-Wother] ! exp: exp '+' exp | exp '-' exp | '(' exp ')' ! ^^^^^^^^^^^ ! 3.34-44: warning: rule useless in grammar [-Wother] ! exp: exp '+' exp | exp '-' exp | '(' exp ')' ! ^^^^^^^^^^^ The interest of being so verbose is dubious. I suspect most of the time nonterminals are not expected to be useless, so the user wants to fix the nonterminal, not remove its rules. And even if the user wanted to get rid of its rules, the position of these rules probably does not help more that just having the name of the nonterminal. This commit discard these messages, marked with '!', and keep the others. In particular, we still report: 2.14-16: warning: rule useless in grammar [-Wother] input: '0' | exp ^^^ All the useless rules (including the '!' ones) are still reported in the reports (xml, text, etc.); only the diagnostics on stderr change. * src/gram.c (grammar_rules_useless_report): Don't complain about useless rules whose lhs is useless. * src/reduce.h, src/reduce.c (reduce_nonterminal_useless_in_grammar): Take a sym_content as argument. Adjust callers. * tests/reduce.at (Useless Rules, Underivable Rules, Reduced Automaton): Adjust. --- NEWS | 44 ++++++++++++++++++++++++++++++++++++++++++++ src/gram.c | 5 ++++- src/print-xml.c | 2 +- src/reduce.c | 7 ++++--- src/reduce.h | 7 ++++++- tests/reduce.at | 43 +++++++------------------------------------ 6 files changed, 66 insertions(+), 42 deletions(-) diff --git a/NEWS b/NEWS index 18771946..e64c6e89 100644 --- a/NEWS +++ b/NEWS @@ -2,6 +2,50 @@ GNU Bison NEWS * Noteworthy changes in release ?.? (????-??-??) [?] +** Diagnostics about useless rules + + In the following grammar, the 'exp' nonterminal is trivially useless. So, + of course, its rules are useless too. + + %% + input: '0' | exp + exp: exp '+' exp | exp '-' exp | '(' exp ')' + + Previously all the useless rules were reported, including those whose + left-hand side is the 'exp' nonterminal: + + warning: 1 nonterminal useless in grammar [-Wother] + warning: 4 rules useless in grammar [-Wother] + 2.14-16: warning: nonterminal useless in grammar: exp [-Wother] + input: '0' | exp + ^^^ + 2.14-16: warning: rule useless in grammar [-Wother] + input: '0' | exp + ^^^ + 3.6-16: warning: rule useless in grammar [-Wother] + exp: exp '+' exp | exp '-' exp | '(' exp ')' + ^^^^^^^^^^^ + 3.20-30: warning: rule useless in grammar [-Wother] + exp: exp '+' exp | exp '-' exp | '(' exp ')' + ^^^^^^^^^^^ + 3.34-44: warning: rule useless in grammar [-Wother] + exp: exp '+' exp | exp '-' exp | '(' exp ')' + ^^^^^^^^^^^ + + Now, rules whose left-hand side symbol is useless are no longer reported + as useless. + + warning: 1 nonterminal useless in grammar [-Wother] + warning: 4 rules useless in grammar [-Wother] + 2.14-16: warning: nonterminal useless in grammar: exp [-Wother] + input: '0' | exp + ^^^ + 2.14-16: warning: rule useless in grammar [-Wother] + input: '0' | exp + ^^^ + +* Noteworthy changes in release ?.? (????-??-??) [?] + ** Bug fixes *** C++ with Variants (lalr1.cc) diff --git a/src/gram.c b/src/gram.c index abd1872f..594d835f 100644 --- a/src/gram.c +++ b/src/gram.c @@ -293,7 +293,10 @@ grammar_rules_useless_report (const char *message) { rule_number r; for (r = 0; r < nrules ; ++r) - if (!rules[r].useful) + /* Don't complain about rules whose LHS is useless, we already + complained about it. */ + if (!reduce_nonterminal_useless_in_grammar (rules[r].lhs) + && !rules[r].useful) complain (&rules[r].location, Wother, "%s", message); } diff --git a/src/print-xml.c b/src/print-xml.c index 81a491c2..f1564244 100644 --- a/src/print-xml.c +++ b/src/print-xml.c @@ -417,7 +417,7 @@ print_grammar (FILE *out, int level) "", i, xml_escape (tag), - reduce_nonterminal_useless_in_grammar (i) + reduce_nonterminal_useless_in_grammar (symbols[i]->content) ? "useless-in-grammar" : "useful"); } xml_puts (out, level + 1, ""); diff --git a/src/reduce.c b/src/reduce.c index 46b38ffc..316833bb 100644 --- a/src/reduce.c +++ b/src/reduce.c @@ -442,10 +442,11 @@ reduce_token_unused_in_grammar (symbol_number i) } bool -reduce_nonterminal_useless_in_grammar (symbol_number i) +reduce_nonterminal_useless_in_grammar (const sym_content *sym) { - aver (ntokens <= i && i < nsyms + nuseless_nonterminals); - return nsyms <= i; + symbol_number n = sym->number; + aver (ntokens <= n && n < nsyms + nuseless_nonterminals); + return nsyms <= n; } /*-----------------------------------------------------------. diff --git a/src/reduce.h b/src/reduce.h index 0dab504c..254f7bc2 100644 --- a/src/reduce.h +++ b/src/reduce.h @@ -24,7 +24,12 @@ void reduce_grammar (void); void reduce_output (FILE *out); bool reduce_token_unused_in_grammar (symbol_number i); -bool reduce_nonterminal_useless_in_grammar (symbol_number i); + +/** Whether symbol \a i is useless in the grammar. + * \pre reduce_grammar was called before. + */ +bool reduce_nonterminal_useless_in_grammar (const sym_content *sym); + void reduce_free (void); extern unsigned nuseless_nonterminals; diff --git a/tests/reduce.at b/tests/reduce.at index c28635eb..c7edb10b 100644 --- a/tests/reduce.at +++ b/tests/reduce.at @@ -172,33 +172,6 @@ input.y:13.1-8: warning: nonterminal useless in grammar: useless8 [-Wother] input.y:14.1-8: warning: nonterminal useless in grammar: useless9 [-Wother] useless9: '9'; ^^^^^^^^ -input.y:6.11-13: warning: rule useless in grammar [-Wother] - useless1: '1'; - ^^^ -input.y:7.11-13: warning: rule useless in grammar [-Wother] - useless2: '2'; - ^^^ -input.y:8.11-13: warning: rule useless in grammar [-Wother] - useless3: '3'; - ^^^ -input.y:9.11-13: warning: rule useless in grammar [-Wother] - useless4: '4'; - ^^^ -input.y:10.11-13: warning: rule useless in grammar [-Wother] - useless5: '5'; - ^^^ -input.y:11.11-13: warning: rule useless in grammar [-Wother] - useless6: '6'; - ^^^ -input.y:12.11-13: warning: rule useless in grammar [-Wother] - useless7: '7'; - ^^^ -input.y:13.11-13: warning: rule useless in grammar [-Wother] - useless8: '8'; - ^^^ -input.y:14.11-13: warning: rule useless in grammar [-Wother] - useless9: '9'; - ^^^ ]]) @@ -287,12 +260,6 @@ not-reduced.y:11.6-19: warning: nonterminal useless in grammar: non_productive [ not-reduced.y:11.6-57: warning: rule useless in grammar [-Wother] | non_productive { /* A non productive action. */ } ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ -not-reduced.y:14.16-56: warning: rule useless in grammar [-Wother] - not_reachable: useful { /* A not reachable action. */ } - ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ -not-reduced.y:17.17-18.63: warning: rule useless in grammar [-Wother] - non_productive: non_productive useless_token - ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ]]) AT_CHECK([[sed -n '/^Grammar/q;/^$/!p' not-reduced.output]], 0, @@ -360,14 +327,18 @@ underivable: indirection; indirection: underivable; ]]) -AT_BISON_CHECK([[input.y]], 0, [], +AT_BISON_CHECK([[-fcaret input.y]], 0, [], [[input.y: warning: 2 nonterminals useless in grammar [-Wother] input.y: warning: 3 rules useless in grammar [-Wother] input.y:5.15-25: warning: nonterminal useless in grammar: underivable [-Wother] + exp: useful | underivable; + ^^^^^^^^^^^ input.y:6.14-24: warning: nonterminal useless in grammar: indirection [-Wother] + underivable: indirection; + ^^^^^^^^^^^ input.y:5.15-25: warning: rule useless in grammar [-Wother] -input.y:6.14-24: warning: rule useless in grammar [-Wother] -input.y:7.14-24: warning: rule useless in grammar [-Wother] + exp: useful | underivable; + ^^^^^^^^^^^ ]]) AT_CHECK([[sed -n '/^Grammar/q;/^$/!p' input.output]], 0,