Hi Martin, Thanks for the reply.
On 2018-02-04 02:17 PM, Martin Sebor wrote: > Printing the suffix is unhelpful because it leads to unnecessary > differences in diagnostics (even in non-template contexts). For > templates with non-type template parameters there is no difference > between, say A<1>, A<1U>, A<(unsigned) 1>, or even A<Green> when > Green is an enumerator that evaluates to 1, so including the suffix > serves no useful purpose. This is the part I don't understand. In Roman's example, spelling foo<10> and foo<10u> resulted in two different instantiations of the template, with different code. So that means it can make a difference, can't it? > In the GCC test suite, it would tend to > cause failures due to differences between the underlying type of > common typedefs like size_t and ptrdiff_t. Avoiding these > unnecessary differences was the main motivation for the change. > Not necessarily just in the GCC test suite but in all setups that > process GCC messages. Ok, I understand. > I didn't consider the use of auto as a template parameter but > I don't think it changes anything. There, just like in other > contexts, what's important is the deduced types and the values > of constants, not the minute details of how they are spelled. Well, it seems like using decltype on a template constant value is a way to make the type of constants important, in addition to their value. I know the standard seems to say otherwise (what Manfred quoted), but the reality seems different. I'm not a language expert so I can't tell if this is a deficiency in the language or not. > That said, it wasn't my intention to make things difficult for > the debugger. I hope so :). > But changing GCC back to include the suffix, > even just in the debug info, isn't a solution. There are other > compilers besides GCC that don't emit the suffixes, and there > even are some that prepend a cast to the number, so if GDB is > to be usable with all these kinds of producers it needs to be > able to handle all of these forms. As I said earlier, there are probably ways to make GDB cope with it. The only solution I saw (I'd like to hear about other ones) was to make GDB ignore the template part in DW_AT_name and re-build it from the DW_TAG_template_* DIEs in the format it expects. It can already do that somewhat, because, as you said, some compilers don't emit the template part in DW_AT_name. Doing so would cause major slowdowns in symbol reading, I've tried it for the sake of experimentation/discussion. I have a patch available on the "users/simark/template-suffix" branch in the binutils-gdb repo [1]. It works for Roman's example, but running the GDB testsuite shows that, of course, the devil is in the details. Consider something like this: template <int *P> struct foo { virtual ~foo() {} }; int n; int main () { foo<&n> f; } The demangled name that GDB will be looking up is "foo<&n>". The debug info about the template parameter only contains the resulting address of n (the value of &n): <2><bf>: Abbrev Number: 11 (DW_TAG_template_value_param) <c0> DW_AT_name : P <c2> DW_AT_type : <0x1ac> <c6> DW_AT_location : 10 byte block: 3 34 10 60 0 0 0 0 0 9f (DW_OP_addr: 601034; DW_OP_stack_value) I don't see how GDB could reconstruct the "&n" in the template, so that's where my idea falls short. Simon [1] https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=shortlog;h=refs/heads/users/simark/template-suffix