[PATCH] D34188: Don't check side effects for functions outside of SCoP

[Sameer AbuAsal via Phabricator via llvm-commits]

sabuasal added inline comments.


================
Comment at: lib/Support/SCEVValidator.cpp:121
 bool polly::isConstCall(llvm::CallInst *Call) {
   if (Call->mayReadOrWriteMemory())
     return false;
----------------
singam-sanjay wrote:
> grosser wrote:
> > singam-sanjay wrote:
> > > For polyhedral analysis, do we also need the function to evaluate to the same value always (not just side effect free) inside the Scop ? I got this notion from the name of the function.
> > > 
> > > If that's the case, is it possible to check for that ? ( I have a feeling that it's not feasible )
> > Yes, that's what we need. I believe that we can assume that if a function does not read memory it will always return the same value.
> > 
> > However, there is another bug that slipped in. I assumed mayReadOrWriteMemory corresponds to is-always-executed. This is not the case, so we should likely limit this to functions that are called in the entry block (or at least post-dominate the entry block).
> > Yes, that's what we need. I believe that we can assume that if a function does not read memory it will always return the same value.
> 
> What about random number generators ?
> 
> > However, there is another bug that slipped in. I assumed mayReadOrWriteMemory corresponds to is-always-executed. This is not the case, so we should likely limit this to functions that are called in the entry block (or at least post-dominate the entry block).
> 
> How does mayReadOrWrite become mustReadOrWrite for those functions ?
> 
> 
> 
Well, random number generators actually modify some object internally to keep trak of the series of random numbers generated so by definition they are not const functions.


Repository:
  rL LLVM

https://reviews.llvm.org/D34188