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Re: [PATCH 1/3] (v2) On-demand locations within string-literals


On 07/28/2016 02:38 PM, Martin Sebor wrote:
On 07/28/2016 02:12 PM, David Malcolm wrote:
On Wed, 2016-07-27 at 23:41 +0100, Manuel López-Ibáñez wrote:
On 27 July 2016 at 15:30, David Malcolm <dmalcolm@redhat.com> wrote:
Perhaps it could live for now in c-format.c, since it is the only
place using it?

Martin Sebor [CC-ed] wants to use it from the middle-end:
   https://gcc.gnu.org/ml/gcc-patches/2016-07/msg01088.html
so it's unclear to me that c-format.c would be a better location.

Fine. He will have to figure out how to get a cpp_reader from the
middle-end, though.

It seems to me that on-demand reconstruction of source locations for
STRING_CST nodes is inherently frontend-specific: unless we have the
frontend record the information in some fe-independent way (which I
assume we *don't* want to do, for space-efficiency), we need to be able
to effectively re-run part of the frontend.

So maybe this needs to be a langhook; the c-family can use the global
cpp_reader * there, and everything else can return a "not supported"
code if a diagnostic requests substring location information (and the
diagnostic needs to be able to cope with that).

The problem with the lanhook approach, as I learned from my first
-Wformat-length attempt, is that it doesn't make the front end
implementation available to LTO.  So passes that run late enough
with LTO (like the latest version of the -Wformat-length pass
does) would not be bale to make use of it.

I'm sorry, I didn't mean to sound like I was dismissing the idea.
I agree that string processing is language and front-end specific.
Having the middle end call back into the front-end also seems like
the right thing to do, not just to make this case work, but others
like it as well.  So perhaps the problem to solve is how to teach
LTO to talk to the front end.  One way to do it would be to build
the front ends as shared libraries.

Martin


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