[PATCH] D142459: [clang] Deprecate uses of GlobalObject::getAlignment

[Guillaume Chatelet via Phabricator via llvm-commits]

gchatelet added inline comments.


================
Comment at: clang/lib/CodeGen/CGCUDANV.cpp:491
           new llvm::LoadInst(Var->getType(), ManagedVar, "ld.managed", false,
-                             llvm::Align(Var->getAlignment()), I);
+                             Var->getAlign().valueOrOne(), I);
       WorkItem.pop_back();
----------------
tra wrote:
> This appears to be a change in behavior. AFAICT, previously used Var->getAlignment() could return alignment value or 0. Now it's value or 1.
> 
> Is it intentional?
The previous statement was constructing an `llvm::Align` from a value, and `llvm::Align` [asserts when the provided value is 0](https://github.com/llvm/llvm-project/blob/4ab2246d486ba30c4b2d654323a0c0b97565c0f1/llvm/include/llvm/Support/Alignment.h#L76-L81). This means that it is undefined to pass the value `0`.

As far as `LoadInst` is concerned it can only accept valid alignments (i.e., powers of two => non zero).

So you're right that it is not strictly NFC and that `*Var->getAlign()`would be a more rigorous transformation but I //think// that converting the `0` value to `1` moves us from UB to semantically valid code.

I don't feel strongly about it though and I'm fine changing this to `*Var->getAlign()` to keep this patch NFC. WDYT?


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  https://reviews.llvm.org/D142459/new/

https://reviews.llvm.org/D142459