[llvm-dev] Multi-Threading Compilers
Johannes Doerfert via llvm-dev
llvm-dev at lists.llvm.org
Fri Mar 27 00:03:31 PDT 2020
On 3/26/20 6:25 AM, Florian Hahn via llvm-dev wrote:
>> On Mar 26, 2020, at 11:09, David Chisnall via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
>> On 26/03/2020 11:06, Florian Hahn via llvm-dev wrote:
>>> One problem is that function passes can add new global, e.g. new
declarations if they introduce new calls. I guess that would require
some locking, but should happen quite infrequently.
>> Can they? I have had to make a pass a ModulePass in the past,
because it added a global to hold a cache. The global was used in only
the function being modified, but the fact that it was a global prevented
the pass from being a FunctionPass.
> Maybe they should not, but I think in practice plenty of function
passes insert new declarations.
> For example, I think Intrinsic::getDeclaration inserts a new
declaration if the requested intrinsic is not yet declared
and a lot of function passes use it.
I think you are unfortunately both correct. As I said before, creating,
modifying, and deleting globals will most likely need explicit
synchronization. It is not too hard to implement though and unlikely to
be a performance bottleneck (IMHO).
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