[PATCH] D36556: [IR] AutoUpgrade ModuleFlagBehavior for PIC and PIE level

[Steven Wu via Phabricator via llvm-commits]

steven_wu added a comment.

In https://reviews.llvm.org/D36556#844596, @dexonsmith wrote:

> Who changed the behaviour?  Can we get them to review the behaviour of the upgrade?
>
> I don't see a general test for PIE level.  Can we add one of those as well?


The PIE test is in the same module.

test/Linker/module-flags-pic-1-a.ll needs to updated because the auto upgrade only happens when you load from bitcode. The texture format is not auto upgradeable and the old value still has valid syntax.



================
Comment at: lib/IR/AutoUpgrade.cpp:2273-2274
+      Type *Int32Ty = Type::getInt32Ty(Context);
+      MD->replaceOperandWith(
+          0, ConstantAsMetadata::get(ConstantInt::get(Int32Ty, After)));
+      return true;
----------------
dexonsmith wrote:
> It's not generally sound to call `MDNode::replaceOperandWith`, unless the nodes are "distinct".  I strongly suspect these nodes are "uniqued", which means that they are semantically constants (with far-too-lenient an API).
> 
> Instead, you should construct a new node to attach to the `NamedMDNode`.
I am pretty sure the MDNode added to ModuleFlags are all uniqued.

I am trying to modify the ModuleFlag here. Attaching new node to module flag is easy but removing is not. Sure, I can reconstruct the entire module flag NamedMDNode, but I am not sure if that is worthwhile if the MDNode is ensured to be uniqued.


https://reviews.llvm.org/D36556