On Fri, Jul 16, 2021 at 12:42 AM Martin Sebor via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> A number of access warnings as well as their supporting
> infrastructure (compute_objsize et al.) are implemented in
> builtins.{c,h} where they (mostly) operate on trees and run
> just before RTL expansion.
>
> This setup may have made sense initially when the warnings were
> very simple and didn't perform any CFG analysis, but it's becoming
> a liability. The code has grown both in size and in complexity,
> might need to examine the CFG to improve detection, and in some
> cases might achieve a better S/R ratio if run earlier. Running
> the warning code on trees is also slower because it doesn't
> benefit from the SSA_NAME caching provided by the pointer_query
> class. Finally, having the code there is also an impediment to
> maintainability as warnings and builtin expansion are unrelated
> to each other and contributors to one area shouldn't need to wade
> through unrelated code (similar for patch reviewers).
>
> The attached change introduces a new warning pass and a couple of
> new source and headers and, as the first step, moves the warning
> code from builtins.{c,h} there. To keep the initial changes as
> simple as possible the pass only runs a subset of existing
> warnings: -Wfree-nonheap-object, -Wmismatched-dealloc, and
> -Wmismatched-new-delete. The others (-Wstringop-overflow and
> -Wstringop-overread) still run on the tree representation and
> are still invoked from builtins.c or elsewhere.
>
> The changes have no functional impact either on codegen or on
> warnings. I tested them on x86_64-linux.
>
> As the next step I plan to change the -Wstringop-overflow and
> -Wstringop-overread code to run on the GIMPLE IL in the new pass
> instead of on trees in builtins.c.
That's the maybe_warn_rdwr_sizes thing?
+ gimple *stmt = gsi_stmt (si);
+ if (!is_gimple_call (stmt))
+ continue;
+
+ check (as_a <gcall *>(stmt));
if (gcall *call = dyn_cast <gcall *> (gsi_stmt (si)))
check (call);
might be more C++-ish.
The patch looks OK - I skimmed it as mostly moving things
around plus adding a new pass.
Thanks,
Richard.
> Martin
>
> PS The builtins.c diff produced by git diff was much bigger than
> the changes justify. It seems that the code removal somehow
> confused it. To make review easy I replaced it with a plain
> unified diff of builtins.c that doesn't suffer from the problem.
