tingwang added a comment.
In D125095#3552451 <https://reviews.llvm.org/D125095#3552451>, @shchenz wrote:
> Thanks for doing this. I am not familiar with the frontend, so I may be
> wrong/stupid in the follow comments : )
> Hope other experts like @hubert.reinterpretcast can give more meaningful
> comments.
>
> I tested on AIX, seems for static variable `static int x = foo();` in global
> scope, even compile with `-bcdtors:csect`, the init function also will not be
> eliminated. Could you please give an example to show why we need the new
> associated metadata for this case? Thanks.
Here is one example to show:
TEST_FOLDER=/tmp/test
mkdir -p $TEST_FOLDER
cd $TEST_FOLDER
cat > libbar.cc <<EOF
int globalVar = 2;
extern "C" int puts(const char *);
int foo() {
puts("foo");
globalVar = 42;
return 30;
}
static int x = foo();
EOF
cat > libbaz.cc <<EOF
extern "C" int puts(const char *);
template <typename = void>
struct A {
~A() { puts("struct A ~A() 2"); }
static A instance;
};
template <typename T> A<T> A<T>::instance;
void *zap() { return &A<>::instance; }
EOF
cat > uselib.cc <<EOF
#include <dlfcn.h>
int main(void) {
void *handle = dlopen("./libbaz.so", RTLD_NOW | RTLD_LOCAL);
dlclose(handle);
}
EOF
g++
===
XLC=g++
$XLC -fno-exceptions -c libbar.cc
rm -f libbar.a
ar qs libbar.a libbar.o
ranlib libbar.a
$XLC -fno-exceptions -c libbaz.cc
$XLC -shared -o libbaz.so libbaz.o libbar.a
$XLC -fno-exceptions -ldl uselib.cc -o uselib -ldl
./uselib
foo
struct A ~A() 2
XLC 16.1.0
==========
XLC=/gsa/rtpgsa/projects/x/xlcmpbld/run/vacpp/16.1.0/aix/daily/191109/bin/xlclang++
$XLC -g -qnoeh -qfuncsect -c libbar.cc
rm -f libbar.a
ar qs libbar.a libbar.o
ranlib libbar.a
$XLC -g -qnoeh -qfuncsect -c libbaz.cc
$XLC -g -qtwolink -G -o libbaz.so libbaz.o libbar.a
$XLC -g -qnoeh uselib.cc -o uselib
./uselib
foo
struct A ~A() 2
clang++ baseline
================
XLC=/home/tingwa/repo/llvm-project-base/dev/build/bin/clang++
$XLC -g -fignore-exceptions -ffunction-sections -c libbar.cc
rm -f libbar.a
ar qs libbar.a libbar.o
ranlib libbar.a
$XLC -g -fignore-exceptions -ffunction-sections -c libbaz.cc
$XLC -g -bcdtors:csect -shared -Wl,-G -o libbaz.so libbaz.o libbar.a
$XLC -g -fignore-exceptions uselib.cc -o uselib
./uselib
struct A ~A() 2
clang++ .ref
============
XLC=/home/tingwa/repo/llvm-project-12514-BE/dev/build/bin/clang++
$XLC -g -fignore-exceptions -ffunction-sections -c libbar.cc
rm -f libbar.a
ar qs libbar.a libbar.o
ranlib libbar.a
$XLC -g -fignore-exceptions -ffunction-sections -c libbaz.cc
$XLC -g -bcdtors:csect -shared -Wl,-G -o libbaz.so libbaz.o libbar.a
$XLC -g -fignore-exceptions uselib.cc -o uselib
./uselib
foo
struct A ~A() 2
As shown in this example: without .ref association, clang++ baseline case will
be wrong, since globalVar is updated in the init function.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D125095/new/
https://reviews.llvm.org/D125095
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