[Bug c++/83799] [8 Regression] bogus "no matching function for call to" error when building llvm

["dmalcolm at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83799

--- Comment #5 from David Malcolm <dmalcolm at gcc dot gnu.org> ---
Author: dmalcolm
Date: Wed Jan 17 15:56:07 2018
New Revision: 256796

URL: https://gcc.gnu.org/viewcvs?rev=256796&root=gcc&view=rev
Log:
Fix failure building LLVM with location wrapper nodes (PR c++/83799)

PR c++/83799 reports a failure building LLVM due to a bogus
"no matching function for call to" error at a callsite like this:
  TLI->getTypeLegalizationCost(DL);
where "DL" is from:
  using TargetTransformInfoImplBase::DL;

The root cause is that type_dependent_expression_p on a USING_DECL
should return true when processing a template, but after r256448 the
the argument at the callsite is a location wrapper around the USING_DECL,
and type_dependent_expression_p erroneously returns false for it, as
it is comparing tree codes, and failing a match, then looking at types.

This prevents cp_parser_postfix_expression from using the
"build_min_nt_call_vec" path for handling the call, instead erroneously
handling it via build_new_method_call (which fails for this case).

This patch fixes the problem by stripping any location wrappers before
the various tree code tests in type_dependent_expression_p.   It fixes
the reduced test case, and the full BasicTargetTransformInfo.ii; after
this patch, the assembly generated for that latter case is identical to
that generated before r256448.

gcc/cp/ChangeLog:
        PR c++/83799
        * pt.c (type_dependent_expression_p): Strip any location wrapper
        before testing tree codes.
        (selftest::test_type_dependent_expression_p): New function.
        (selftest::cp_pt_c_tests): Call it.

gcc/testsuite/ChangeLog:
        PR c++/83799
        * g++.dg/wrappers/pr83799.C: New test case.


Added:
    trunk/gcc/testsuite/g++.dg/wrappers/pr83799.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/pt.c
    trunk/gcc/testsuite/ChangeLog