[LLVMdev] dense maps

[Owen Anderson]

IIRC, assertions are enabled by default if you're building from SVN, and disabled by default if you're building from a release tarball.

--Owen

On Jan 26, 2012, at 3:11 PM, Preston Briggs wrote:

> 
> My problem was that the constructor for DenseMap has an undocumented constraint.
> 
> explicit DenseMap(unsigned NumInitBuckets = 0) {
>   init(NumInitBuckets);
> }
> 
> if given an explicit argument, requires that the argument be a power of 2.
> 
> It's checked by an assert in init(), but for some reason my code didn't trip the assertion.
> Is there a special way I must make to enable asserts?
> 
> Thanks,
> Preston
> 
> 
> On Wed, Jan 25, 2012 at 9:44 PM, Preston Briggs <preston.briggs at gmail.com> wrote:
> Reading the LLVM Programmer's Manual, the description of DenseSet mentions:
> 
> Note that DenseSet has the same requirements for the value type that DenseMap has.
> 
> But when I read about DenseMap, I don't really see any requirements for the values, just a warning about space.  On the other hand, the keys have special requirements, which aren't entirely clear to me.  It says
> 
> Finally, you must implement a partial specialization of DenseMapInfo for the key that you want, if it isn't already supported. This is required to tell DenseMap about two special marker values (which can never be inserted into the map) that it needs internally.
> 
> Will my code fail to compile if the required specialization of DenseMapInfo is not present?
> 
> I wonder all these things because I've tripped across a problem where a method hangs repeatably, and I don't see the problem.
> 
> typedef SmallVector<BasicBlock *, 4> Frontier;
> DenseMap<BasicBlock *, Frontier> frontier(blocks*3/2);
> 
> BasicBlock *Xblock = ...
> 
> errs() << "start\n";
> Frontier &f = frontier[Xblock];    // Xblock is not yet represented in frontier
> errs() << "finish\n";
> 
> It compiles fine (as part of a function-level pass), but the call frontier[Xblock] fails (hangs) after several successful calls.  I tried replacing the declaration of frontier with 
> 
> DenseMap<BasicBlock *, Frontier *> frontier(blocks*3/2);
> 
> but trip over the same problem in the same place.
> 
> I've used the DenseMap successfully in several other places, so I'm not sure that's gone wrong here.
> 
> Any ideas?
> 
> Thanks,
> Preston
> 
> 
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