https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119482
--- Comment #3 from ak at gcc dot gnu.org ---
I ran a full comparison now. There is actually a significant regression between
g++-13 and g++-14, but -15 is roughly the same as -14. All are significantly
slower than clang:
clang++-19 -std=gnu++20 Interpreter.cpp -I ../../.. -I ../.. -w -S -o x.s -O2
ran
1.17 ± 0.19 times faster than clang++-18 -std=gnu++20 Interpreter.cpp -I
../../.. -I ../.. -w -S -o x.s -O2
5.10 ± 0.51 times faster than g++-13 -std=gnu++20 Interpreter.cpp -I
../../.. -I ../.. -w -S -o x.s -O2
5.91 ± 0.60 times faster than g++-15 -std=gnu++20 Interpreter.cpp -I
../../.. -I ../.. -w -S -o x.s -O2
6.15 ± 0.61 times faster than g++-14 -std=gnu++20 Interpreter.cpp -I
../../.. -I ../.. -w -S -o x.s -O2
For clang flatten just based on cfi_startproc gcc actually generates more
functions:
% grep -c cfi_startproc interpreter-clang.s
570
% grep -c cfi_startproc interpreter-gcc.s
610
but gcc indeed generates much more code:
text data bss dec hex filename
311591 1536 1 313128 4c728 interpreter-clang.o
783346 8 2 783356 bf3fc interpreter-gcc.o
So yes there might be a difference in flatten semantics
I'm attaching a input file that works for clang if you want to look yourself.
