[RFC][PATCH] c++/46476 - implement -Wunreachable-code-return

Jeff Law jeffreyalaw@gmail.com
Sun Nov 28 20:09:51 GMT 2021



On 11/26/2021 5:18 AM, Richard Biener via Gcc-patches wrote:
> This implements a subset of -Wunreachable-code, unreachable code
> after a return stmt.  Contrary to the previous attemt at CFG
> construction time this implements the bits during GIMPLE lowering
> where there are still all GIMPLE return stmts in the IL.
>
> The lowering phase keeps track of whether stmts can fallthru
> which is used to determine if the following stmt is reachable.
> The implementation only considers labels here.
>
> The fallthru flag is transparently extended to allow tracking
> a reason for non-fallthruness which is used to mark returns.
>
> This patch runs in to the same stray return/gcc_unreachable as the
> previous one and thus requires cleanup across the GCC code base
> which seems controversical.  So I'm putting this on hold unless
> I receive some OK for cleanup in any way, meaning this isn't
> going to make stage3.
>
> Sorry.
>
> Richard.
>
> 2021-11-26  Richard Biener  <rguenther@suse.de>
>
> 	PR c++/46476
> gcc/cp/
> 	* decl.c (finish_function): Set input_location to
> 	BUILTINS_LOCATION around the code building the return 0
> 	for main().
> 	* cp-gimplify.c (genericize_if_stmt): Avoid optimizing if (true)
> 	and if (false) when -Wunreachable-code-return is in effect.
>
> gcc/
> 	* common.opt (Wunreachable-code): Re-enable.
> 	(Wunreachable-code-return): New diagnostic, enabled by
> 	-Wextra and -Wunreachable-code.
> 	* doc/invoke.texi (Wunreachable-code): Document.
> 	(Wunreachable-code-return): Likewise.
> 	* gimple-low.c: Include diagnostic.h.
> 	(struct cft_reason): New.
> 	(lower_data::cannot_fallthru): Make a cft_reason.
> 	(lower_stmt): Diagnose unreachable stmts after a return.
> 	* Makefile.in (insn-emit.o-warn): Disable
> 	-Wunreachable-code-return.
>
> gcc/testsuite/
> 	* c-c++-common/Wunreachable-code-return-1.c: New testcase.
I wouldn't object to this moving forward.  I've already ACK'd the cleanups.

Jeff



More information about the Gcc-patches mailing list