Richard Guenther <richard.guent...@gmail.com> writes: >> * The C++ frontend emits some warnings on code which is known to be >> never executed, which the C frontend does not. This leads to some >> warnings compiling code in gcc. I think it is reasonable to fix this >> in the C++ frontend. > > Or just amend the C frontend to also warn in these cases?
We could do that, but we would have to adjust gcc's code base to avoid the warnings. For example, in insn-modes.c we emit code like this: #define MODE_MASK(m) \ ((m) >= HOST_BITS_PER_WIDE_INT) \ ? ~(unsigned HOST_WIDE_INT) 0 \ : ((unsigned HOST_WIDE_INT) 1 << (m)) - 1 MODE_MASK (0), /* VOID */ With the current C++ frontend, this issues a warning about a shift larger than the word size. The C frontend sees that the condition is a constant, so it does not issue any warnings about the unexecuted side of the conditional. This is done by manipulating skip_evaluation in c_parser_conditional_expression and testing it in build_binary_op. Ian
