On 08/29/2013 10:17 PM, Benjamin Thaut wrote:
How about LTO, when statically linking it should be possible to optimize
away the indirection.
Rainer Schuetze stated that some linkers are capable of doing this
optimizations. But I don't know aynthing further about this topic.
module libA;
export int var;
int* _imp_var = &var; // created by compiler
module foo;
import libA;
void bar()
{
auto val = var; // creates val = *_imp_var;
}
Yes that would work. Still there must be a reason why microsoft doesn't
do stuff like that in their C++ toolchain. Its certanly going to cost
performance.
I just tested it and it works.
lib.c
int var = 0xdeadbeaf;
int* _imp_var = &var;
main.c
#include <stdio.h>
extern int* _imp_var;
void main()
{
printf("%d\n", *_imp_var);
}
cl /c /O2 /GL lib.c
cl /O2 /GL main.c lib.obj
get objconv from http://www.agner.org/optimize/
objconv -fasm main.exe
Search for deadbeaf in main.asm to get the symbol number (?_1176).
It directly loads the variable.
mov edx, dword ptr [?_1176]
