[llvm] r226588 - Add an assertion and prefer a crash over an infinite loop.

[Adrian Prantl]

> Begin forwarded message:
> 
> Subject: Re: [llvm] r226588 - Add an assertion and prefer a crash over an infinite loop.
> From: "Duncan P. N. Exon Smith" <dexonsmith at apple.com>
> Date: January 20, 2015 at 10:53:38 AM PST
> Cc: llvm-commits at cs.uiuc.edu
> To: Adrian Prantl <aprantl at apple.com>
> 
> 
>> On 2015 Jan 20, at 10:03, Adrian Prantl <aprantl at apple.com> wrote:
>> 
>> Author: adrian
>> Date: Tue Jan 20 12:03:37 2015
>> New Revision: 226588
>> 
>> URL: http://llvm.org/viewvc/llvm-project?rev=226588&view=rev
>> Log:
>> Add an assertion and prefer a crash over an infinite loop.
>> 
>> Modified:
>>   llvm/trunk/lib/IR/DebugInfo.cpp
>> 
>> Modified: llvm/trunk/lib/IR/DebugInfo.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/DebugInfo.cpp?rev=226588&r1=226587&r2=226588&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/IR/DebugInfo.cpp (original)
>> +++ llvm/trunk/lib/IR/DebugInfo.cpp Tue Jan 20 12:03:37 2015
>> @@ -527,12 +527,15 @@ bool DISubprogram::Verify() const {
>>        while ((IA = DL.getInlinedAt()))
>>          DL = DebugLoc::getFromDILocation(IA);
>>        DL.getScopeAndInlinedAt(Scope, IA);
>> +        assert(Scope && "debug location has no scope");
>>        assert(!IA);
>>        while (!DIDescriptor(Scope).isSubprogram()) {
>>          DILexicalBlockFile D(Scope);
>>          Scope = D.isLexicalBlockFile()
>>                      ? D.getScope()
>>                      : DebugLoc::getFromDILexicalBlock(Scope).getScope();
>> +          if (!Scope)
>> +            llvm_unreachable("lexical block file has no scope");
> 
> It's strange that this isn't simply an assertion:
> 
>    assert(Scope && "lexical block file has no scope");
> 
> But I guess that's so that it crashes even when NDEBUG?  (Is that
> reliable?)

Yes, that’s the intention (and llvm_unreachable is meant to be used that way).
> 
> If that's the reason, you should probably add a comment to that
> effect since otherwise I'm likely to switch it to an assert next
> time I look at it ;).
> 
> (Also, do you know when this situation arises?)

Happened to me when I compiled an old .ll file without the MDLocation upgrade.

-- adrian

> 
>>        }
>>        if (!DISubprogram(Scope).describes(F))
>>          return false;
>> 
>> 
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