[LLVMdev] Possible issue with DenseMap when using AliasSetTracker

[Nick Lewycky]

Oliver Horst wrote:
> Dear All,
>
> while willing to assist developers to adhere strictly to coding guidelines, I
> wrote the attached program called "alias-detector". The program's intent is to
> utilize the BasicAliasAnalysis to get a list of aliases for each pointer in a
> certain program code. First it initializes clang as frontend, executes the
> EmitLLVMOnlyAction, and then processes the produced Module with the following
> three passes:
> 1. BasicAliasAnalysis -- The basic alias analysis
> 2. AliasTrackerPass -- BasicBlockPass that creates an AliasSet for each pointer
> in the analyzed code (line 261 and line 94 respectively)
> 3. AliasDetectorPass -- BasicBlockPass that prints the AliasSet of each pointer
> in the analyzed code (line 264 and line 133 respectively)
>
> The first Pass seems to work flawlessly. However, the 2nd Pass fails due to a
> segmentation fault that somehow seems to be related to the DenseMap data
> structure. However, I wasn't able to pin down the issue. Accordingly, I'd like
> to ask for an advise. Maybe someone with more knowledge of the code basis could
> have a closer look on the topic and could tell whether this is really an issue
> of the DenseMap or me using it incorrectly.
>
> I'm currently using llvm and clang in release version 3.2.
> Please find attached the "alias-detector" program and its backtrace.

The problem is that you never added a DataLayout object to the 
PassManager (it's an ImmutablePass) and AliasSetTracker appears to be 
assuming you have one.

However, I don't see such a bug with llvm on trunk, and the line numbers 
don't line up. Perhaps this has already been fixed?

Nick