> I am not sure I understand the intended semantics of the UnnamedAddr argument > to GetOrCreateLLVMGlobal. Is it “this use does not care about the specific > address”? Because, if so, the (existing) logic is completely backwards: we > need to be *clearing* the flag on the global if the argument is ever *false*. > And that seems like the most reasonable semantics, frankly. > > Also, the idea in the existing code that all runtime variables are > unnamed_addr seems bogus to me. __dso_handle is a specific example of a > variable whose address value *is* semantically important. This sort of thing > would be important if there were any plausible transformations at all that > involve unnamed_addr on external variable declarations. > > Also, the assertion is wrong: if something introduces a “runtime" declaration > (e.g. by just declaring and using a global variable with the right name) > before CodeGen emits its first intrinsic use of it, the declaration will not > be marked unnamed_addr. > > So, basically, right now, this entire code path is useless and wrong. Is > there a plan to apply it in situations where it wouldn’t be useless, i.e. to > non-runtime user declarations?
So, on how the patch is organized: * The structure the patch uses is that when the variable is first created, its unnamed_addr is set to the value of the argument. * We then check that no user expect that a variable is unnamed_addr when in fact it isn't. I tried to make the check more strict by asserting that Entry->getUnnamedAddr() == UnnamedAddr, but that fails deep down in some objc cases that create runtime variables and access them as regular ones. But to the more important point: Should we be adding unnamed_addr in the first place? I am not sure. Back in http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20110110/037796.html Chris asked if we should. I could not find the entire discussion (the patch that ended up being committed is simpler) and I am still not sure exactly when CreateRuntimeVariable should be used. An alternative patch that simply never sets it in CreateRuntimeVariable is attached. Cheers, Rafael
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