glr2.cc: disable incorrect warnings from GCC6 to 9

For instance with GCC8:

    616. regression.at:1560: testing Lex and parse params: glr2.cc ...
    tests/regression.at:1560: COLUMNS=1000; export COLUMNS; NO_TERM_HYPERLINKS=1; export NO_TERM_HYPERLINKS;  bison --color=no -fno-caret  -o input.cc input.y
    tests/regression.at:1560: $CXX $CXXFLAGS $CPPFLAGS  $LDFLAGS -o input input.cc $LIBS
    stderr:
    input.cc: In member function 'YYRESULTTAG glr_stack::yyresolveValue(glr_state*)':
    input.cc:1796:10: error: potential null pointer dereference [-Werror=null-dereference]
       return yypred ? &(asItem(this) - yypred)->getState() : YY_NULLPTR;
              ^~~~~~
    input.cc:1796:10: error: potential null pointer dereference [-Werror=null-dereference]
       return yypred ? &(asItem(this) - yypred)->getState() : YY_NULLPTR;
              ^~~~~~
    cc1plus: all warnings being treated as errors

It complains that the implicit this in yypred might be null.  It fears
it because of loops such as

    for (glr_state* yys = firstTopState();
         yys != yystateStack.yysplitPoint;
         yys = yys->pred())
      yyn += 1;

that could possibly set yys to null, since yys->pred might return
null.  However, the warning is incorrect, since in C++ `this` cannot
be null.  GCC 10 no longer emits this warning.

GCC 7 also complains many times about glr_stack::yyresolveLocations
when NDEBUG is enabled (when it is not, YYASSERT (yyoption !=
YY_NULLPTR) is probably enough to pacify GCC):

    616. regression.at:1560: testing Lex and parse params: glr2.cc ...
    tests/regression.at:1560: COLUMNS=1000; export COLUMNS; NO_TERM_HYPERLINKS=1; export NO_TERM_HYPERLINKS;  bison --color=no -fno-caret  -o input.cc input.y
    tests/regression.at:1560: $CXX $CXXFLAGS $CPPFLAGS  $LDFLAGS -o input input.cc $LIBS
    stderr:
    input.cc: In member function 'void glr_stack::yyresolveLocations(glr_state*, int)':
    input.cc:3061:46: error: potential null pointer dereference [-Werror=null-dereference]
                     yyrhsloc[0].getState().yyloc = yyoption->state()->yyloc;
                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
    input.cc:3061:46: error: potential null pointer dereference [-Werror=null-dereference]
                     yyrhsloc[0].getState().yyloc = yyoption->state()->yyloc;
                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
    input.cc:3061:46: error: potential null pointer dereference [-Werror=null-dereference]
                     yyrhsloc[0].getState().yyloc = yyoption->state()->yyloc;
                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
    input.cc: In member function 'YYRESULTTAG glr_stack::yyresolveValue(glr_state*)':
    input.cc:3061:46: error: potential null pointer dereference [-Werror=null-dereference]
                     yyrhsloc[0].getState().yyloc = yyoption->state()->yyloc;
                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
    input.cc:3061:46: error: potential null pointer dereference [-Werror=null-dereference]
                     yyrhsloc[0].getState().yyloc = yyoption->state()->yyloc;
                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
    input.cc:3061:46: error: potential null pointer dereference [-Werror=null-dereference]
                     yyrhsloc[0].getState().yyloc = yyoption->state()->yyloc;
                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
    input.cc:3061:46: error: potential null pointer dereference [-Werror=null-dereference]
                     yyrhsloc[0].getState().yyloc = yyoption->state()->yyloc;
                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
    input.cc:3061:46: error: potential null pointer dereference [-Werror=null-dereference]
                     yyrhsloc[0].getState().yyloc = yyoption->state()->yyloc;
                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
    input.cc:3061:46: error: potential null pointer dereference [-Werror=null-dereference]
                     yyrhsloc[0].getState().yyloc = yyoption->state()->yyloc;
                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~

* data/skeletons/glr2.cc (YY_IGNORE_NULL_DEREFERENCE_BEGIN)
(YY_IGNORE_NULL_DEREFERENCE_BEGIN): New.
(glr_state::pred, glr_stack::yyresolveLocations): Use them.

1 files changed, 10 insertions, 3 deletions

diff --git a/TODO b/TODO
index 3f4d1978..c692b9f9 100644
--- a/TODO
+++ b/TODO
@@ -158,9 +158,12 @@ Les catégories d'avertissements incluent :
 Line -1 and -3 should mention CATEGORIE, not CATEGORY.
 
 * Bison 3.8
-** Rewrite glr.cc
-*** glr.c
-Get rid of scaffolding in glr.c.
+** Rewrite glr.cc (currently glr2.cc)
+*** Remove jumps
+We can probably replace setjmp/longjmp with exceptions.  That would help
+tremendously other languages such as D and Java that probably have no
+similar feature.  If we remove jumps, we probably no longer need _Noreturn,
+so simplify `b4_attribute_define([noreturn])` into `b4_attribute_define`.
 
 *** Coding style
 Move to our coding conventions.  In particular names such as yy_glr_stack,
@@ -178,6 +181,10 @@ There are many places where pointers should be replaced with references.
 Don't use YYSTYPE and YYLTYPE but parser::semantic_type and
 parser::location_type.  Undefine YYSTYPE and YYLTYPE.
 
+*** glr.c
+When glr2.cc fully replaces glr.cc, get rid of the glr.cc scaffolding in
+glr.c.
+
 * Chains
 ** Unit rules / Injection rules (Akim Demaille)
 Maybe we could expand unit rules (or "injections", see