c++: 'this' capture clobbered during recursive inst [PR116756]

Here during instantiation of generic lambda's op() [with I = 0] we
substitute into the call self(self, cst<1>{}) which requires recursive
instantiation of the same op() [with I = 1] (which isn't deferred due to
lambda's deduced return type.  During this recursive instantiation, the
DECL_EXPR case of tsubst_stmt clobbers LAMBDA_EXPR_THIS_CAPTURE to point
to the child op()'s specialized capture proxy instead of the parent's,
and the original value is never restored.

So later when substituting into the openSeries call in the parent op()
maybe_resolve_dummy uses the 'this' proxy belonging to the child op(),
which leads to a context mismatch ICE during gimplification of the
proxy.

An earlier version of this patch fixed this by making instantiate_body
save/restore LAMBDA_EXPR_THIS_CAPTURE during a lambda op() instantiation.
But it seems cleaner to avoid overwriting LAMBDA_EXPR_THIS_CAPTURE in the
first place by making it point to the non-specialized capture proxy, and
instead call retrieve_local_specialization as needed, which is what this
patch implements.  It's natural then to not clear LAMBDA_EXPR_THIS_CAPTURE
after parsing/regenerating a lambda.

	PR c++/116756

gcc/cp/ChangeLog:

	* lambda.cc (lambda_expr_this_capture): Call
	retrieve_local_specialization on the result of
	LAMBDA_EXPR_THIS_CAPTURE for a generic lambda.
	* parser.cc (cp_parser_lambda_expression): Don't clear
	LAMBDA_EXPR_THIS_CAPTURE.
	* pt.cc (tsubst_stmt) <case DECL_EXPR>: Don't overwrite
	LAMBDA_EXPR_THIS_CAPTURE with the specialized capture.
	(tsubst_lambda_expr): Don't clear LAMBDA_EXPR_THIS_CAPTURE
	afterward.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp1z/constexpr-if-lambda7.C: New test.

Reviewed-by: Jason Merrill <jason@redhat.com>

0 files changed, 0 insertions, 0 deletions