[Bug lto/53777] New: [lto] lto does not propagate optimization flags from command lines given at "compilation time"

[vincenzo.innocente at cern dot ch]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53777

             Bug #: 53777
           Summary: [lto] lto does not propagate optimization flags from
                    command lines given at "compilation time"
    Classification: Unclassified
           Product: gcc
           Version: 4.7.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: lto
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: vincenzo.innoce...@cern.ch


we are used to mix in the same library code compiled with -O2 and -Os
Lto seems to ignore the options used in the "compilation" steps
It does honor "pragma GCC optimize" though

example

cat optopt.cc
// #pragma GCC optimize ("0")

void bar(int);

inline void foo(int i, int j) {
  if (i>0) bar(i);
  if (j>0) bar(j);
  if (i>0) bar(j);
  if (j>0) bar(i);
 };


void foo1(int i, int j) {
  foo(i,j);
}
void foo2(int i, int j) {
  foo(i,j);
}
void foo3(int i, int j) {
  foo(i,j);
}

c++ -flto -fno-fat-lto-objects -Os -c optopt.cc -fPIC
c++ -flto -O2 -shared optopt.o -fPIC -o optopt.so; nm -C optopt.so
….
                 U bar(int)
00000000000007a0 T foo1(int, int)
0000000000000740 T foo2(int, int)
00000000000006e0 T foo3(int, int)
….
c++ -flto -Os -shared optopt.o -fPIC -o optopt.so; nm -C optopt.so
….
                 U bar(int)
00000000000006e0 t foo(int, int) [clone .local.0.2370]
000000000000071c T foo1(int, int)
000000000000071a T foo2(int, int)
0000000000000718 T foo3(int, int)
…


if I decomment the pragma I get what intended
c++ -flto -fno-fat-lto-objects -O2 -c optopt.cc -fPIC
c++ -flto -O2 -shared optopt.o -fPIC -o optopt.so; nm -C optopt.so
                 U bar(int)
00000000000006e0 t foo(int, int) [clone .local.0.2370]
0000000000000760 T foo1(int, int)
0000000000000750 T foo2(int, int)
0000000000000740 T foo3(int, int)

due to PR53776 I cannot specify Os using a pragma. so I am a bit stuck