[PATCH] D15996: Avoid undefined behavior in LinkAllPasses.h

[David Blaikie via llvm-commits]

On Tue, Jan 12, 2016 at 8:41 AM, Mehdi Amini <mehdi.amini at apple.com> wrote:

> You need to be careful that an LTO build won’t inline and eliminate this.
>

fair - but these calls, if they'd executed, would've been totally bogus,
right? (they would've crashed/null dereferenced, etc)

So somehow this code is live without it actually executing.

To come back to the underlying issue: What is it we're trying to solve
here? What entities are we trying to preserve & why are more
traditional/normal ways of preserving them insufficient? (sorry if this is
too much of a derailment/the rest  of you have enough context here, feel
free to go on without me ;))


>
> —
> Mehdi
>
> On Jan 12, 2016, at 8:02 AM, David Blaikie via llvm-commits <
> llvm-commits at lists.llvm.org> wrote:
>
> Do you need to call anything? Could you just take the address of the
> function and return it, stuff it in a global, or otherwise escape it?
>
> On Tue, Jan 12, 2016 at 12:02 AM, Dimitry Andric via llvm-commits <
> llvm-commits at lists.llvm.org> wrote:
>
>> dim added a subscriber: grosser.
>>
>> ================
>> Comment at: include/llvm/LinkAllPasses.h:191
>> @@ -190,3 +196,3 @@
>>        llvm::RGPassManager RGM;
>> -      ((llvm::RegionPass*)nullptr)->runOnRegion((llvm::Region*)nullptr,
>> RGM);
>>        llvm::AliasSetTracker X(*(llvm::AliasAnalysis*)nullptr);
>> ----------------
>> @grosser, you originally added this part in rL117263 ("Reference
>> RegionPass to stop it being eliminated"), do you have any suggestions? If
>> the goal is to to unsure RegionPass.cpp is linked in, I think we can call
>> `RegionPass::createPrinterPass()` instead.
>>
>>
>> http://reviews.llvm.org/D15996
>>
>>
>>
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