Close https://github.com/llvm/llvm-project/issues/93497
The root cause of the problem is, we mark the variable from other
modules as constnant in LLVM incorrectly. This patch fixes this problem
by not emitting the defintition for non-const available external
variables. Since the non const available externally variable is not
helpful to the optimization.
Close https://github.com/llvm/llvm-project/issues/60996.
Previously, clang will try to import function bodies from other module
units to get more optimization oppotunities as much as possible. Then
the motivation becomes the direct cause of the above issue.
However, according to the discussion in SG15, the behavior of importing
function bodies from other module units breaks the ABI compatibility. It
is unwanted. So the original behavior of clang is incorrect. This patch
choose to not import function bodies from other module units in all
cases to follow the expectation.
Note that the desired optimized BMI idea is discarded too. Since it will
still break the ABI compatibility after we import function bodies
seperately.
The release note will be added seperately.
There is a similar issue for variable definitions. I'll try to handle
that in a different commit.
