[LLVMdev] LazyValueInfo.getPredicateAt

[Hal Finkel]

----- Original Message -----
> From: "Artur Pilipenko" <apilipenko at azulsystems.com>
> To: llvmdev at cs.uiuc.edu
> Sent: Thursday, April 16, 2015 7:22:03 AM
> Subject: [LLVMdev] LazyValueInfo.getPredicateAt
> 
> Hi,
> 
> Is it intentional that LazyValueInfo.getPredicateAt doesn't solve for
> the value and only takes assumptions into account?

Yes. That function is used from only one place in JumpThreading:

    } else if (CondBr && CondConst && CondBr->isConditional()) {
      // There might be an invariant in the same block with the conditional
      // that can determine the predicate.

      LazyValueInfo::Tristate Ret =
        LVI->getPredicateAt(CondCmp->getPredicate(), CondCmp->getOperand(0),
                            CondConst, CondCmp);
      if (Ret != LazyValueInfo::Unknown) {
...

and handles a situation that can only happen with @llvm.assume (where new information regarding a value's range is introduced in the block containing the conditional; normally this can only happen on edges and is picked up by getValueOnEdge, etc.)

Why do you ask?

 -Hal 

> 
> getPredicateAt gets lattice value from cache using getValueAt call:
> LVILatticeVal LazyValueInfoCache::getValueAt(Value *V, Instruction
> *CxtI) {
>    ...
>    LVILatticeVal Result;
>    mergeAssumeBlockValueConstantRange(V, Result, CxtI);
>    ...
>    return Result;
> }
> 
> Other get functions in LazyValueInfoCache solve to obtain the result:
> LVILatticeVal LazyValueInfoCache::getValueInBlock(Value *V,
> BasicBlock *BB,
>                                                    Instruction *CxtI)
>                                                    {
> 
>    ...
>    pushBlockValue(std::make_pair(BB, V));
>    solve();
>    LVILatticeVal Result = getBlockValue(V, BB);
>    mergeAssumeBlockValueConstantRange(V, Result, CxtI);
>    ...
>    return Result;
> }
> 
> Thanks,
> Artur
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> 

-- 
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory