c++: per-scope, per-signature lambda discriminators

This implements ABI-compliant lambda discriminators.  Not only do we
have per-scope counters, but we also distinguish by lambda signature.
Only lambdas with the same signature will need non-zero
discriminators.  As the discriminator is signature-dependent, we have
to process the lambda function's declaration before we can determine
it.  For templated and generic lambdas the signature is that of the
uninstantiated lambda -- not separate for each instantiation.

With this change, gcc and clang now produce the same lambda manglings
for all these testcases.

	gcc/cp/
	* cp-tree.h (LAMBDA_EXPR_SCOPE_SIG_DISCRIMINATOR): New.
	(struct tree_lambda_expr): Add discriminator_sig bitfield.
	(recrd_lambda_scope_sig_discriminator): Declare.
	* lambda.cc (struct lambda_sig_count): New.
	(lambda_discriminator): Add signature vector.
	(start_lambda_scope): Adjust.
	(compare_lambda_template_head, compare_lambda_sig): New.
	(record_lambda_scope_sig_discriminator): New.
	* mangle.cc (write_closure_type): Use the scope-sig discriminator for
	ABI >= 18.  Emit abi mangling warning if needed.
	* module.cc (trees_out::core_vals): Stream the new discriminator.
	(trees_in::core_vals): Likewise.
	* parser.cc (cp_parser_lambda_declarator_opt): Call
	record_lambda_scope_sig_discriminator.
	* pt.cc (tsubst_lambda_expr): Likewise.
	libcc1/
	* libcp1plugin.cc (plugin_start_lambda_closure_class_type):
	Initialize the per-scope, per-signature discriminator.
	gcc/testsuite/
	* g++.dg/abi/lambda-sig1-18.C: New.
	* g++.dg/abi/lambda-sig1-18vs17.C: New.
	* g++.dg/cpp1y/lambda-mangle-1-18.C: New.

1 files changed, 7 insertions, 1 deletions

diff --git a/gcc/cp/mangle.cc b/gcc/cp/mangle.cc
index a62c975..e97428e 100644
--- a/gcc/cp/mangle.cc
+++ b/gcc/cp/mangle.cc
@@ -1810,7 +1810,13 @@ write_closure_type_name (const tree type)
 
   write_method_parms (parms, /*method_p=*/1, fn);
   write_char ('E');
-  write_compact_number (LAMBDA_EXPR_SCOPE_ONLY_DISCRIMINATOR (lambda));
+  if ((LAMBDA_EXPR_SCOPE_SIG_DISCRIMINATOR (lambda)
+       != LAMBDA_EXPR_SCOPE_ONLY_DISCRIMINATOR (lambda))
+      && abi_warn_or_compat_version_crosses (18))
+    G.need_abi_warning = true;
+  write_compact_number (abi_version_at_least (18)
+			? LAMBDA_EXPR_SCOPE_SIG_DISCRIMINATOR (lambda)
+			: LAMBDA_EXPR_SCOPE_ONLY_DISCRIMINATOR (lambda));
 }
 
 /* Convert NUMBER to ascii using base BASE and generating at least