https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82803
Yann Droneaud <yann at droneaud dot fr> changed:
What |Removed |Added
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CC| |yann at droneaud dot fr
--- Comment #8 from Yann Droneaud <yann at droneaud dot fr> ---
Created attachment 46903
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=46903&action=edit
An artificial test case for gcc to emit 17 calls to __tls_get_addr()
Using Thread Local Storage (TLS) is a pain: the issue reported here still apply
on latest GCC.
I've code such as
static struct state *state(void) __attribute__((pure));
static struct state *state(void)
{
static __thread struct state s;
return &s;
}
int do(void)
{
struct state * const s = state();
int res;
/* do something */
return res;
}
Once compiled, code for my real function contains 6 calls to __tls_get_addr().
Which is far more than expected. And far more than necessary.
Clang compile the same code and emit a single call to __tls_get_addr(). Both on
Linux amd64, -O3 -fPIC.
The attached testcase is an example which is designed to trigger 17 calls to
__tls_get_addr(). As you will see, there's about one per conditional + function
call pair.
Once again, clang is able to emit code with a single call to __tls_get_addr().
You can check for yourself: https://godbolt.org/z/QVGjka
