On Thursday, 29 August 2013 at 21:40:08 UTC, Martin Nowak wrote:
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]
I was doubting my idea, but you conviced me :P
