On Fri, 4 Aug 2023 at 23:28, Bradley Lucier via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> The patch at the end adds a warning when a tail/sibling call cannot be
> optimized for various reasons.
>
> I built and tested GCC with and without the patch with configuration
>
> Configured with: ../../gcc-mainline/configure --enable-languages=c
> --disable-multilib --prefix=/pkgs/gcc-mainline --disable-werror
>
> There were some changes in the test results, but I can't say that they
> look substantive:
>
> diff -C 2 summary.log ../gcc-mainline
> *** summary.log Thu Aug 3 22:56:13 2023
> --- ../gcc-mainline/summary.log Thu Aug 3 19:42:33 2023
> ***************
> *** 14,22 ****
> === g++ Summary ===
>
> ! # of expected passes 239234
> # of unexpected failures 5
> # of expected failures 2087
> ! # of unsupported tests 10566
> ! /home/lucier/programs/gcc/objdirs/gcc-mainline-new/gcc/xg++ version
> 14.0.0 20230802 (experimental) (GCC)
>
> === gcc tests ===
> --- 14,22 ----
> === g++ Summary ===
>
> ! # of expected passes 239262
> # of unexpected failures 5
> # of expected failures 2087
> ! # of unsupported tests 10562
> ! /home/lucier/programs/gcc/objdirs/gcc-mainline/gcc/xg++ version
> 14.0.0 20230802 (experimental) (GCC)
>
> === gcc tests ===
> ***************
> *** 155,164 ****
> === gcc Summary ===
>
> ! # of expected passes 192553
> # of unexpected failures 109
> # of unexpected successes 19
> # of expected failures 1506
> ! # of unsupported tests 2623
> ! /home/lucier/programs/gcc/objdirs/gcc-mainline-new/gcc/xgcc version
> 14.0.0 20230802 (experimental) (GCC)
>
> === libatomic tests ===
> --- 155,164 ----
> === gcc Summary ===
>
> ! # of expected passes 192563
> # of unexpected failures 109
> # of unexpected successes 19
> # of expected failures 1506
> ! # of unsupported tests 2619
> ! /home/lucier/programs/gcc/objdirs/gcc-mainline/gcc/xgcc version
> 14.0.0 20230802 (experimental) (GCC)
>
> === libatomic tests ===
>
> I then configured and built GCC with
>
> ../../gcc-mainline/configure CXX="/pkgs/gcc-mainline-new/bin/g++
> -Wdisabled-optimization" --enable-languages=c --disable-multilib
> --prefix=/pkgs/gcc-mainline-test --disable-werror --disable-bootstrap
>
> to test the new warning. The warnings are of the form, e.g.,
>
> ../../../gcc-mainline/gcc/tree-vect-stmts.cc:11990:44: warning: cannot
> apply sibling-call optimization: callee required more stack slots than
> the caller [-Wdisabled-optimization]
>
> These are the number of times this warning was triggered building stage1:
>
> grep warning: build.log | grep sibling | sed 's/^.*://' | sort | uniq -c
> 259 callee required more stack slots than the caller
> [-Wdisabled-optimization]
> 43 callee returns a structure [-Wdisabled-optimization]
>
> If this patch is OK, someone else will need to commit it for me.
>
> Brad
>
> gcc/Changelog
>
> * calls.cc (maybe_complain_about_tail_call) Add warning when
> tail or sibling call cannot be optimized.
Hi Bradley,
I don't have comments on the patch, but a new warning will also
require a corresponding entry in doc/invoke.texi.
Thanks,
Prathamesh
>
> diff --git a/gcc/calls.cc b/gcc/calls.cc
> index 1f3a6d5c450..b95c876fda8 100644
> --- a/gcc/calls.cc
> +++ b/gcc/calls.cc
> @@ -1242,10 +1242,12 @@ void
> maybe_complain_about_tail_call (tree call_expr, const char *reason)
> {
> gcc_assert (TREE_CODE (call_expr) == CALL_EXPR);
> - if (!CALL_EXPR_MUST_TAIL_CALL (call_expr))
> - return;
> -
> - error_at (EXPR_LOCATION (call_expr), "cannot tail-call: %s", reason);
> + if (CALL_EXPR_MUST_TAIL_CALL (call_expr))
> + error_at (EXPR_LOCATION (call_expr), "cannot tail-call: %s", reason);
> + else if (flag_optimize_sibling_calls)
> + warning (OPT_Wdisabled_optimization,
> + "cannot apply sibling-call optimization: %s", reason);
> + return;
> }
>
> /* Fill in ARGS_SIZE and ARGS array based on the parameters found in
>
>
