[clang] [Clang][CodeGen] Emit dereferenceable and nofree for indirect arguments (PR #213347)

[Sayan Sivakumaran via cfe-commits]

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@@ -3238,6 +3235,23 @@ void CodeGenModule::ConstructAttributeList(StringRef Name,
       assert(!Align.isZero());
       Attrs.addAlignmentAttr(Align.getQuantity());
 
+      // According to [basic.stc.auto], parameters have automatic storage
+      // duration. Therefore, the underlying object of this pointer will not be
+      // freed during the function's execution. If the parameter is realigned,
+      // this may not be true, but realignment does not currently occur for
+      // non-byval. Hmm....
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sivakusayan wrote:

Okay, fixed. To put it in my own words to make sure I understand:

The point of `IndirectRealign` is to get around scenarios where the default stack alignment is not strict enough for types that have high alignment requirements. This can happen with `byval` when the data itself is passed on the stack. However, without `byval` there is no stack alignment we need to worry about - the copy in the caller should already be aligned. So `IndirectRealign` is non-applicable.

https://github.com/llvm/llvm-project/pull/213347