How to do in clang the gcc -O optimizing option equivalent?
gcc -O3 -o tes tes.cpp
on clang ...?
You do exactly the same.
clang -O3 -o tes tes.cpp
Related
I want to evaluate an AVX2 program written in c-intrinsics using gcc 5.4.0 and clang 3.8 for compiling and using perf , valgrind and IACA for evaluating and analysis. I Exactly want the same optimization approach so I read this related question clang optimization and this page for gcc optimization option for gcc but I still doubted .
gcc -O2 and gcc -O3 is my basis and want the same in clang since Clang do auto-vectorization in -O2 and I don't want it when comparing the results with gcc -O2 and want it when -O3 is enabled in gcc. so the question is what command should I use in clang that is corresponded to these commands in gcc :
First:
compile :
gcc -Wall -O2 -march=native -masm=intel -c -S "%f"
build:
gcc -Wall -O2 -mavx2 -o "%e" "%f"
Second:
compile :
gcc -Wall -O3 -march=native -masm=intel -c -S "%f"
build:
gcc -Wall -O3 -mavx2 -o "%e" "%f"
I have converted c program into assembly code using following commands in LLVM :
clang -emit-llvm matrix.c -c -o matrix.bc
llc -march=alpha matrix.bc -o matrix.s
Now how to convert matrix.s assembly file into executable file of alpha.
How to do that?
clang can also be used
clang matrix.s -L [additional library locations] -mllvm -Wall -g -L. -Wl,-pie -I. -I[additional include locations] -o [executable output]
Adjust the flags as your needs dictate.
EDIT
Without the need for other includes or libraries just call:
clang matrix.s -mllvm -Wall -g -Wl,-pie -o matrix.out
gcc experts,
I'm trying to use gcc lto with library archives, as the gcc comes with my system (RedHat Enterprise Linux 5.7) doesn't work with -flto (neither for my Ubuntu 14.10), so I build binutils && gcc from scratch.
Here is what I did:
1. Build binutils-2.22 with --enable-plugins
2. Build gcc-4.7.2 with --with-plugin-ld=/path/to/ld/built/in/step1 --enable-lto
3. Then for the following simple test:
// 1.c:
int foo(void)
{ return 0; }
// 2.c:
extern int foo(void)
int main(void)
{ return foo(); }
The following can get foo() inlined:
my_gcc -O3 -flto -c -o 1.o 1.c
my_gcc -O3 -flto -c -o 2.o 2.c
my_gcc -O3 -flto -o a.out 1.o 2.o
While the following can't:
my_gcc -O3 -flto -c -o 1.o 1.c
my_gcc -O3 -flto -c -o 2.o 2.c
my_ar cr --plugin <my_gcc>/libexec/gcc/x86_64-redhat-linux/4.7.2/liblto_plugin.so 1.a 1.o
my_ar cr --plugin <my_gcc>/libexec/gcc/x86_64-redhat-linux/4.7.2/liblto_plugin.so 2.a 2.o
gcc -O3 -flto -fuse-linker-plugin -o a.out 1.a 2.a
As the building system for the product I'm working on has to use archives, then what I can do to let lto work with library archive?
Your help will be much much appreciated.
Thanks a lot.
When linking, the order in which the libraries are listed on the command line, matters. So when compiling from the archives, you should swap 1.a and 2.a:
gcc -O3 -flto -fuse-linker-plugin -o a.out 2.a 1.a
I tested with gcc 4.9.2 and the disassembly, obtained with objdump -d a.out, shows that foo() is being inlined.
I am new to Squirrel based scripting. Whenever I am trying to compile the program using the GCC compiler. I am getting the following error:
symbol(s) not found for architecture x86_64
I am trying to compile the code on a 64bit mac.
I am new so please excuse me if this is a really dumb question.
To solve the compilation you have to modify the Makefile under SQUIRREL3/sq/ by removing the -s flag from the g++ command.
Example:
sq64:
g++ -O2 -s -m64 -fno-exceptions -fno-rtti -D_SQ64 -o $(OUT) $(SRCS) $(INCZ) $(LIBZ) $(LIB)
becomes:
sq64:
g++ -O2 -m64 -fno-exceptions -fno-rtti -D_SQ64 -o $(OUT) $(SRCS) $(INCZ) $(LIBZ) $(LIB)
Hope it helps.
I'm trying to create a shared library with my gcc. It's a gcc for vxworks (thats probably the problem...).
I use the gcc as following:
./gcc -shared -B/path/to/gnutools/bin -o test.so test.c
Result:
/path/to/ld: -r and -shared may not be used together
collect2: ld returned 1 exit status
If I try the same with the linux gcc, there's no problem. So i guess the gcc for VxWorks automatically passes the -r (or -i, which is the same and results in the same) flag to the linker. Is there a way to suppress this?
Greetz
marty
PS: making it static is not really an alternative...
Try compile object file separately with -fPIC and then link:
gcc -Wall -fPIC -c -o test.o test.c
gcc -Wall -shared -o test.so test.o
Another suggestion is to use libtool (at least to figure out the correct flags).
A workaround may be to go directly with ld:
ld -shared -o test.so test.o -lc