This is based on what is recommended by both Scott Meyers, in 'Effective
C++', and Andrei Alexandrescu and Herb Sutter in 'C++ Coding Standards'.
Use a static_cast on void* rather than directly use a reinterpret_cast,
which can have nefarious effects on objects. However, even though following
this guideline is good practice in general, I am not quite sure how relevant
it is when applied to conversions from POD to objects. Actually, it might
very well be the opposite: isn't this exactly what reinterpret_cast is for?
What we really want *is* to transmit the memory map as a series of bytes,
which, if I am correct, falls into the kind of "low level" hack for which
this cast is meant.
In any case, this silences the warning, which will be greatly appreciated by
anyone using variants with a compiler supporting -fstrict-aliasing.
* data/variant.hh (as): Here.
* tests/c++.at (Exception safety, C++ Variant-based Symbols, Variants):
Don't use NO_STRICT_ALIAS_CXXFLAGS (revert commit
ddb9db15), as type punning
is no longer an issue.
* tests/atlocal.in, configure.ac (NO_STRICT_ALIAS_CXXFLAGS): Remove
definition.
* examples/local.mk (NO_STRICT_ALIAS_CXXFLAGS): Remove from AM_CXXFLAGS.
* doc/bison.texi: Don't mention type punning issues.
done
# Clang++ 3.2+ reject C code generated by Flex.
gl_WARN_ADD([-Wno-null-conversion], [WARN_NO_NULL_CONVERSION_CXXFLAGS])
- # Variants break strict aliasing analysis.
- gl_WARN_ADD([-fno-strict-aliasing], [NO_STRICT_ALIAS_CXXFLAGS])
CXXFLAGS=$save_CXXFLAGS
AC_LANG_POP([C++])
fi
{]b4_parse_assert_if([
YYASSERT (tname == typeid (T).name ());
YYASSERT (sizeof (T) <= S);])[
- return reinterpret_cast<T&> (buffer.raw);
+ {
+ void *dummy = buffer.raw;
+ return *static_cast<T*> (dummy);
+ }
}
/// Const accessor to a built \a T (for %printer).
{]b4_parse_assert_if([
YYASSERT (tname == typeid (T).name ());
YYASSERT (sizeof (T) <= S);])[
- return reinterpret_cast<const T&> (buffer.raw);
+ {
+ const void *dummy = buffer.raw;
+ return *static_cast<const T*> (dummy);
+ }
}
/// Swap the content with \a other, of same type.
types are actually used. This may waste space in some cases.
@item
-Our implementation is not conforming with strict aliasing rules. Alias
-analysis is a technique used in optimizing compilers to detect when two
-pointers are disjoint (they cannot ``meet''). Our implementation breaks
-some of the rules that G++ 4.4 uses in its alias analysis, so @emph{strict
-alias analysis must be disabled}. Use the option
-@option{-fno-strict-aliasing} to compile the generated parser.
-
-@item
There might be portability issues we are not aware of.
@end itemize
TEST_LOG_COMPILER = $(top_srcdir)/examples/test
AM_CXXFLAGS = \
- $(NO_STRICT_ALIAS_CXXFLAGS) \
$(WARN_CXXFLAGS) $(WARN_CXXFLAGS_TEST) $(WERROR_CXXFLAGS)
## ------------ ##
CFLAGS="$NO_WERROR_CFLAGS @WERROR_CFLAGS@"
CXXFLAGS="$NO_WERROR_CXXFLAGS @WERROR_CXXFLAGS@"
-# C++ variants break strict aliasing analysis.
-NO_STRICT_ALIAS_CXXFLAGS='@NO_STRICT_ALIAS_CXXFLAGS@'
-
# If 'exit 77'; skip all C++ tests; otherwise ':'.
BISON_CXX_WORKS='@BISON_CXX_WORKS@'
]])
AT_BISON_CHECK([-o list.cc list.yy])
-AT_COMPILE_CXX([list], [$NO_STRICT_ALIAS_CXXFLAGS list.cc])
+AT_COMPILE_CXX([list], [list.cc])
AT_PARSER_CHECK([./list], 0, [],
[12
123
]])
AT_BISON_CHECK([-o list.cc list.yy])
-AT_COMPILE_CXX([list], [$NO_STRICT_ALIAS_CXXFLAGS list.cc])
+AT_COMPILE_CXX([list], [list.cc])
AT_PARSER_CHECK([./list], 0,
[(0, 1, 2, 4)
])
}
]])
AT_BISON_CHECK([[-o input.cc --report=all input.yy]])
-AT_COMPILE_CXX([input], [[$NO_STRICT_ALIAS_CXXFLAGS input.cc]])
+AT_COMPILE_CXX([[input]])
AT_PARSER_CHECK([[./input aaaas]], [[2]], [[]],
[[exception caught: reduction