[PATCH] D34874: [ArgPromotion] Remove llvm.dbg.value on removed argument

[Mikael Holmén via llvm-commits]

On 07/10/2017 10:46 PM, David Blaikie wrote:
> I suspect removing this isn't the right option - changing its value to 
> 'undef' (as done in the other review you sent, for arguments that were 
> actually promoted/changed their type) is probably best.
> 

Yes I submitted that "other" version where I change it to undef after 
Reid's suggestion.

Regards,
Mikael

> Nothing's going to work perfectly here. The user's going to be confused 
> by the missing parameter, or the debuggers going to be confused when it 
> tries to call the function with this parameter & it doesn't match the 
> ABI anymore, etc... - I don't think there's a good answer at the moment.
> 
> On Fri, Jun 30, 2017 at 8:27 AM Reid Kleckner via Phabricator via 
> llvm-commits <llvm-commits at lists.llvm.org 
> <mailto:llvm-commits at lists.llvm.org>> wrote:
> 
>     rnk added inline comments.
> 
> 
>     ================
>     Comment at: lib/Transforms/IPO/ArgumentPromotion.cpp:135
>     +
>     +      BasicBlock &BB = F->getEntryBlock();
>     +      SmallVector<Instruction*, 8> InstrsToRemove;
>     ----------------
>     There's no reason to believe the only uses of the argument will
>     appear in the entry block. I think you really want to do
>     `I->replaceAllUsesWith(undef)` to replace all metadata uses of the
>     argument. Some other pass (instcombine?) can clean up the useless
>     dbg.value instructions. That's what the dead argument elimination
>     pass does, anyway.
> 
> 
>     https://reviews.llvm.org/D34874
> 
> 
> 
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