gccclanginlining

Can gcc or clang inline functions that are not in the same compilation unit?

Say I have a function with the inline keyword in a compilation unit.

If I have

// math.h
inline int sum(int x, int y);

and

// math.c
inline int sum(int x, int y)
{
   return x + y;
}

and

// main.c
#include "math.h"

int main(int argc, char **argv)
{
    return sum(argc,argc);
}

And building with

gcc -O3 -c math.c -o math.o
gcc -O3 -c main.c -o main.o
gcc math.o main.o

Will an optimizing compiler inline sum? Can gcc or clang inline functions from other compilation units?

Solution

  • GCC can (and often will) inline functions from different TUs when you compile with LTO enabled. For this you need to add -flto to CFLAGS/CXXFLAGS and LDFLAGS.