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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.

artless noise
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Cheng
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1 Answers1

2

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.

bcmpinc
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