Re: [PATCH] avoid bogus -Wstringop-truncation when inlining (PR 84480)

[Jeff Law <law at redhat dot com>]

On 02/21/2018 02:19 PM, Martin Sebor wrote:
> The attached patch eliminates -Wstringop-truncation false
> positives reported in bug 84480 - bogus -Wstringop-truncation
> despite assignment with an inlined string literal.  It does
> that by delegating early strncpy checks during folding to
> the same machinery in tree-ssa-strlen that looks for a NUL
> assignment to the destination the next statement.
> 
> The patch also adds inlining context to the warnings via
> the %G directive.
> 
> Tested on x86_64-linux with no regressions.
> 
> Martin
> 
> gcc-84480.diff
> 
> 
> PR tree-optimization/84480 - bogus -Wstringop-truncation despite assignment with an inlined string literal
> 
> gcc/ChangeLog:
> 
> 	PR tree-optimization/84480
> 	* gimple-fold.c (gimple_fold_builtin_strcpy): Move warnings
> 	to maybe_diag_stxncpy_trunc.  Call it.
> 	* tree-ssa-strlen.c (maybe_diag_stxncpy_trunc): Integrate warnings
> 	from gimple_fold_builtin_strcpy.  Print inlining stack.
> 	(handle_builtin_stxncpy): Print inlining stack.
> 	* tree-ssa-strlen.h (maybe_diag_stxncpy_trunc): Declare.
> 
> gcc/testsuite/ChangeLog:
> 
> 	PR tree-optimization/84480
> 	* c-c++-common/Wstringop-truncation.c: Adjust text of expected warnings.
> 	* g++.dg/warn/Wstringop-truncation-1.C: New test.
In general our guidelines are that the users of a .h file should include
any dependencies rather than having the .h file itself include other .h
files (Now that we've detangled the header files we may want to revisit
that guideline, but that's not a gcc-8 item).

It looks like gimple-fold.c and tree-ssa-strlen.c already have the
prereqs.  So in theory you should be able to just remove the bogus
#includes from tree-ssa-strlen.h.

In general we want to avoid adding more warnings to folding code.  But I
think the argument here is that we're already trying to warn within the
folder and just doing a poor job -- so we're removing that
implementation and delegating the warning to a better implementation.
Right?

So I think you just need to remove the bogus #includes from
tree-ssa-strlen and this is OK.

jeff