This is the mail archive of the
gcc-help@gcc.gnu.org
mailing list for the GCC project.
lto optimization
- From: Aurelien Buhrig <aurelien dot buhrig dot gcc at gmail dot com>
- To: gcc-help at gcc dot gnu dot org
- Date: Wed, 4 May 2016 12:57:06 +0200
- Subject: lto optimization
- Authentication-results: sourceware.org; auth=none
Hi,
I'm trying to generate LTO optimized code (with -O2 -flto).
The code is very simple:
int *SP;
int popInt(void) {return *--SP;}
void pushInt(int v) {*SP++ = v;}
void add (void) { pushInt(popInt()+popInt()); }
When the 3 global functions popInt, pushInt and add are in the same
compilation unit, the lto optimization works as expected and generates
something like
-*(SP -2) += *(SP-1);
SP--;
But when add is in a different compilation unit, gcc cannot succeed in
doing such an optimization at link time. Worse, it does not inline the
popInt function (but it inlines pushInt, so lto are performed).
I tried using the gcse options which are not enabled with O2, O3,
adding -finline-functions and tuning inline limits without success.
Any hint how I could get the same behavior with separated compilation unit ?
This is a gcc 4.6 on a private target.
Thanks,
AurÃlien