[PATCH] D14602: Switch lto codegen to using diagnostic handlers

[Duncan P. N. Exon Smith via llvm-commits]

> On 2015-Nov-11, at 18:55, Yunzhong Gao <Yunzhong_Gao at playstation.sony.com> wrote:
> 
> ygao created this revision.
> ygao added subscribers: rafael, dexonsmith, pcc, joker.eph, llvm-commits.
> 
> With r252791, the C api will install a default diagnostic handler to print to sLastErrorString, therefore
> we no longer need to pass around this sLastErrorString to any the LTOCodeGenerator methods.
> 
> This patch removes the std::string& argument from a number of C++ LTO API calls and instead
> makes them use the installed diagnostic handler. This would also improve consistency of diagnostic
> handling infrastructure: if an LTO client used lto_codegen_set_diagnostic_handler() to install a
> custom error handler, we do not want some error messages to go through the custom error handler,
> and some other error messages to go into sLastErrorString.

Sounds awesome.

> The part that I am not entirely sure about is what should happen when there is no installed
> diagnostic handler at all. In this patch, the fall-back is to print the message to stderr. For this case
> to happen, if the client is using the C api, the client must have explicitly called
> lto_codegen_set_diagnostic_handler(nullptr), and maybe the intention is to not print any error at all?
> I am not sure.

Since `lto_codegen_set_diagnostic_handler()` is the only interface for
diagnostics, I think it should set the diagnostic handler back to the
default diagnostic handler, not to stderr.

> http://reviews.llvm.org/D14602
> 
> Files:
> include/llvm/LTO/LTOCodeGenerator.h
> lib/LTO/LTOCodeGenerator.cpp
> tools/llvm-lto/llvm-lto.cpp
> tools/lto/lto.cpp
> 
> <D14602.40000.patch>