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.
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
