Hi.
I'm building libgcc for a "iamcu" target (Pentium-like but with
soft-fp emulation, the only x86 with SoftFP I know) with
--enable-target-optspace.
It works properly but I noticed that code the size for many arithmetic
functions is much more larger than for soft-fp emulation provided by
LLVM's compiler_rt library.
For example addsf3 (addition of 2 floats) is 0.5K in compiler_rt and 1K in gcc!
I double-checked compiler options and they are correct: -Os.
Is it because of
a) compiler_rt doesn't perform some checks (FP exception for example) or
b) compiler_rt is incorrect in some corner cases or
c) inefficient implementation in libgcc?
Did anyone face with this problem?
How to reproduce:
First you need to build gcc for iamcu:
INSTALL=<your install dir>
TARGET=i586-intel-elfiamcu
./configure --host=x86_64-unknown-linux-gnu --enable-target-optspace
--target=${TARGET} --prefix=${INSTALL} --with-demangler-in-ld
--enable-languages=c MAKEINFO=missing --disable-multilib
--disable-libitm --disable-libatomic --disable-libssp
--disable-libquadmath --with-newlib && make -j $(nproc) && make
install
libgcc
Let's get size of two float addition operation:
nm -S -t dec --defined-only
$(INSTALL)/lib/gcc/i586-intel-elfiamcu/4.9.3/libgcc.a | grep _addsf3
I get:
00000000 00001039 T __addsf3
So the size is ~1K
compiler_rt
svn co http://llvm.org/svn/llvm-project/compiler-rt/trunk compiler-rt
cd compiler_rt/lib/builtins
Compile: $(INSTALL)/bin/i586-intel-elfiamcu-gcc -Os addsf3.c -c
Check function size: nm -S -t dec addsf3.o
I get:
00000000 00000522 T __addsf3
So the size is ~0.5K.
Why so large difference in libgcc and compiler_rt for the same functionality?
Thanks.
-- Zinovy Nis.
