`clang -fpic -fno-semantic-interposition` may set dso_local on variables for -fpic.
GCC folks consider there are 'address interposition' and 'semantic interposition',
and 'disabling semantic interposition' can optimize function calls but
cannot change variable references to use local aliases
(https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100483).
This patch removes dso_local for variables in
`clang -fpic -fno-semantic-interposition` mode so that the built shared objects can
work with copy relocations. Building llvm-project tiself with
-fno-semantic-interposition (D102453) should now be safe with trunk Clang.
Example:
```
// a.c
int var;
int *addr() { return var; }
// old: cannot be interposed
movslq .Lvar$local(%rip), %rax
// new: can be interposed
movq var@GOTPCREL(%rip), %rax
movslq (%rax), %rax
```
The local alias lowering for `GlobalVariable`s is kept in case there is a
future option allowing local aliases.
Reviewed By: rnk
Differential Revision: https://reviews.llvm.org/D102583
Currently clang does not emit device template variables
instantiated only in host functions, however, nvcc is
able to do that:
https://godbolt.org/z/fneEfferY
This patch fixes this issue by refactoring and extending
the existing mechanism for emitting static device
var ODR-used by host only. Basically clang records
device variables ODR-used by host code and force
them to be emitted in device compilation. The existing
mechanism makes sure these device variables ODR-used
by host code are added to llvm.compiler-used, therefore
they are guaranteed not to be deleted.
It also fixes non-ODR-use of static device variable by host code
causing static device variable to be emitted and registered,
which should not.
Reviewed by: Artem Belevich
Differential Revision: https://reviews.llvm.org/D102237
For -fgpu-rdc mode, static device vars in different TU's may have the same name.
To support accessing file-scope static device variables in host code, we need to give them
a distinct name and external linkage. This can be done by postfixing each static device variable with
a distinct CUID (Compilation Unit ID) hash.
Since the static device variables have different name across compilation units, now we let
them have external linkage so that they can be looked up by the runtime.
Reviewed by: Artem Belevich, and Jon Chesterfield
Differential Revision: https://reviews.llvm.org/D85223
Fangrui Song