[Lldb-commits] [RFC] Type lookup for template types is broken...

Greg Clayton via lldb-commits lldb-commits at lists.llvm.org
Tue May 8 09:25:06 PDT 2018


I think for display purposes, the type name should include all of the <params>. If I have two variables, both using class C, but both have different template parameters, I want to see that in the class name and have that properly show up in the variable view. LLDB doesn't actually care about the name that is in the DWARF because we will show the type name by grabbing it from the lldb_private::CompilerType which will end up being correct. Other debuggers might just display "C" if that is what is in the DWARF. So I would caution against just putting the type basename without params in the DWARF itself.

Greg


> On May 8, 2018, at 9:12 AM, <paul.robinson at sony.com> <paul.robinson at sony.com> wrote:
> 
> So….  if the name in the type entry did not include the <params> then the indexing would automatically do what you want; you would need to reconstruct the <params> from the template parameter children of the DIE.  Would that help?
> On the LLVM side we have debated the merits of <params> in the name back and forth.  I would have to investigate the current state of the world; I know that for PS4 we prefer to have the children and not put <params> in the name, while others prefer it the other way around.  If LLDB came out preferring not to have a decorated name, it should not be hard to accommodate that in Clang.
> Not sure where gcc/gdb stand on this point.
> --paulr
>   <>
> From: friss at apple.com [mailto:friss at apple.com] 
> Sent: Tuesday, May 08, 2018 12:07 PM
> To: Greg Clayton
> Cc: Robinson, Paul; lldb-commits at lists.llvm.org
> Subject: Re: [Lldb-commits] [RFC] Type lookup for template types is broken...
>  
>  
> 
> 
> On May 8, 2018, at 9:04 AM, Greg Clayton <clayborg at gmail.com <mailto:clayborg at gmail.com>> wrote:
>  
> The only way for us to find all classes whose type is "C" is to add the entry for all template classes named "C", so I would vote to add them as it is accurate. Do we currently add one for "C<12, 16>”?
>  
> Yes we do, not sure it is actually useful.
>  
> Fred
> 
> 
>  
> Greg
> 
> 
> On May 8, 2018, at 8:58 AM, Frédéric Riss via lldb-commits <lldb-commits at lists.llvm.org <mailto:lldb-commits at lists.llvm.org>> wrote:
>  
> 
> 
> 
> On May 8, 2018, at 8:30 AM, paul.robinson at sony.com <mailto:paul.robinson at sony.com> wrote:
>  
> 
> 
> 
> -----Original Message-----
> From: lldb-commits [mailto:lldb-commits-bounces at lists.llvm.org <mailto:lldb-commits-bounces at lists.llvm.org>] On Behalf
> Of Pavel Labath via lldb-commits
> Sent: Tuesday, May 08, 2018 10:48 AM
> To: friss at apple.com <mailto:friss at apple.com>
> Cc: lldb-commits at lists.llvm.org <mailto:lldb-commits at lists.llvm.org>
> Subject: Re: [Lldb-commits] [RFC] Type lookup for template types is
> broken...
> 
> Well.. it encodes some assumptions about how a class name looks like,
> which
> are probably valid for C++, but they don't have to hold for any language
> frontend LLVM supports. That said, I am not saying this is worth the
> trouble of adding a special "these are the additional names you are to
> insert into the index" channel that clang should use to communicate this
> (I
> wouldn't be surprised if we make even stronger assumptions elsewhere). I
> was just curious about what your thoughts here were.
> 
> If you add an accelerator entry for "C" what does it point to?  All the
> instantiations of "C"?  The DWARF does not describe the template, only
> the concrete instances.
>  
> Yes, there would be a “C” entry for every instantiation of C.
>  
> Fred
> 
> 
> --paulr
> 
> 
> 
> On Tue, 8 May 2018 at 15:29, Frédéric Riss <friss at apple.com <mailto:friss at apple.com>> wrote:
> 
> 
> 
> 
> On May 8, 2018, at 2:23 AM, Pavel Labath <labath at google.com <mailto:labath at google.com>> wrote:
> 
> 
> I am still building a picture for myself of how the accelerator tables
> and
> 
> our name lookup works, but from what I managed to learn so far, adding
> an
> 
> accelerator for "C" seems like a useful thing to do. However, this does
> go
> 
> beyond what the DWARF 5 spec says we should do (we are only required to
> add
> 
> the DW_AT_name string). We are still free to add any extra entries we
> like,
> 
> but if we're going to be relying on this, we should try to get some of
> this
> 
> into the next version of the spec.
> 
> 
> 
> On Mon, 7 May 2018 at 22:19, Frédéric Riss via lldb-commits <
> lldb-commits at lists.llvm.org <mailto:lldb-commits at lists.llvm.org>> wrote:
> 
> 
> (...At least when using accelerator tables)
> 
> 
> 
> If you apply the following patch, TestClassTemplateParameterPack.py will
> 
> 
> start failing:
> 
> 
> diff --git
> 
> 
> a/packages/Python/lldbsuite/test/lang/cpp/class-template-parameter-
> pack/main.cpp
> 
> b/packages/Python/lldbsuite/test/lang/cpp/class-template-parameter-
> pack/main.cpp
> 
> 
> index 90e63b40f..304872a15 100644
> ---
> 
> 
> a/packages/Python/lldbsuite/test/lang/cpp/class-template-parameter-
> pack/main.cpp
> 
> 
> +++
> 
> 
> b/packages/Python/lldbsuite/test/lang/cpp/class-template-parameter-
> pack/main.cpp
> 
> 
> @@ -37,7 +37,7 @@ template <> struct D<int, int, bool> : D<int, int> {
> 
> 
> 
> 
> 
>  int main (int argc, char const *argv[])
>  {
> -    C<int,16,32> myC;
> +    C<int,16,32> myC; //% self.runCmd("settings set
> 
> 
> target.experimental.inject-local-vars false")
> 
> 
>      C<int,16> myLesserC;
>      myC.member = 64;
>      (void)C<int,16,32>().isSixteenThirtyTwo();
> 
> 
> 
> The test does things like invoke methods on temporary template objects:
> //% self.expect("expression -- C<int, 16>().isSixteenThirtyTwo()",
> 
> 
> DATA_TYPES_DISPLAYED_CORRECTLY, substrs = ["false"])
> 
> 
> The above expression currently works because there’s a local of type
> 
> 
> C<int, 16>. With injected locals, the type is made readily available to
> Clang. No type lookup is required for this to work in this setup.
> 
> 
> If you stop injecting locals, the test fails. We don’t provide the
> 
> 
> information to Clang to understand what C is. The reason is that when
> Clang
> 
> parses “C<int , 16>”, it is going to ask about “C”, not the fully
> templated
> 
> name. Our accelerator tables contain references to the full names, but
> not
> 
> to C alone and we never find it. If I change Clang and dsymutil to add
> an
> 
> accelerator for “C” each time an instance of C is seen then it nearly
> works. I just need this additional lldb patch:
> 
> 
> diff --git a/source/Symbol/TypeMap.cpp b/source/Symbol/TypeMap.cpp
> index 2838039ad..d2f2026bf 100644
> --- a/source/Symbol/TypeMap.cpp
> +++ b/source/Symbol/TypeMap.cpp
> @@ -227,8 +227,11 @@ void TypeMap::RemoveMismatchedTypes(const
> 
> 
> std::string &type_scope,
> 
> 
>        } else {
>          // The type we are currently looking at doesn't exists in a
> 
> 
> namespace
> 
> 
>          // or class, so it only matches if there is no type scope...
> -        keep_match =
> -            type_scope.empty() &&
> type_basename.compare(match_type_name)
> 
> 
> == 0;
> 
> 
> +        if (type_scope.empty()) {
> +          keep_match = type_basename.compare(match_type_name) == 0 ||
> +            (strlen(match_type_name) > type_basename.size() &&
> +             match_type_name[type_basename.size()] == '<');
> +        }
>        }
>      }
> 
> 
> 
> I didn’t post this as a Phabricator review as it requires changes in
> llvm
> 
> 
> before doing anything in LLDB and I wanted to make sure we agree this is
> the right thing to do. I’m also not sure if this works out of the box on
> platforms without accelerator tables.
> 
> 
> It won't work "out of the box", but it should be fairly simple to change
> our indexing code to add the extra entries, so that a lookup for "C"
> works
> 
> the same way in both cases. BTW, how were you planning to compute the
> untemplated string ("C"). Will you just strip everything after the first
> '<' character, or were you thinking of something more fancy?
> 
> 
> 
> AFAIK, there are no fully qualified names in the debug info we generate
> so taking what’s before the first ‘<‘ should always return the class name.
> Does this logic seem flawed?
> 
> 
> Fred
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