[llvm] r198290 - BasicAA: Fix value equality and phi cycles

[Arnold]

Updated comments, used isPotentiallyReachable, and renamed isValueEqual to isValueEqualInPotentialCycles in r198400

Thanks,
Arnold

> On Jan 1, 2014, at 8:36 PM, Nick Lewycky <nicholas at mxc.ca> wrote:
> 
>> On 01/01/2014 08:24 PM, Nick Lewycky wrote:
>>> On 01/01/2014 07:31 PM, Arnold Schwaighofer wrote:
>>> Author: arnolds
>>> Date: Wed Jan  1 21:31:36 2014
>>> New Revision: 198290
>> 
>> I don't entirely understand why the fix isn't to speculate less often in
>> aliasPHI?
>> 
>>>    // Are we checking for alias of the same value?
>>> -  if (V1 == V2) return MustAlias;
>>> +  if (isValueEqual(V1, V2)) return MustAlias;
>> 
>> This demands a massive explanation of what on earth is going on. Of
>> course %x mustalias %x! (Yes, I've read the PR and understand it what's
>> going on, but I'd much rather see code that explicitly dealt with the
>> "we're in a loop and speculating on PHIs case" broken out.)
> 
> Er, I mean as a comment in the code.
> 
> Nick
> 
>> 
>>> +bool BasicAliasAnalysis::isValueEqual(const Value *V, const Value *V2) {
>>> +  if (V != V2)
>>> +    return false;
>>> +
>>> +  const Instruction *Inst = dyn_cast<Instruction>(V);
>>> +  if (!Inst)
>>> +    return true;
>>> +
>>> +  // Use the dominance if available.
>>> +  DT = getAnalysisIfAvailable<DominatorTree>();
>>> +  if (DT) {
>>> +    if (VisitedPhiBBs.size() > MaxNumPhiBBsValueDominanceCheck)
>>> +      return false;
>>> +
>>> +    // Make sure that the visited phis are dominated by the Value.
>>> +    for (SmallPtrSet<const BasicBlock *, 8>::iterator
>>> +             PI = VisitedPhiBBs.begin(),
>>> +             PE = VisitedPhiBBs.end();
>>> +         PI != PE; ++PI)
>>> +      if (!DT->dominates(Inst, *PI))
>>> +        return false;
>> 
>> I haven't thought really hard about this, but did you want to use
>> llvm::isPotentiallyReachable?
>> 
>>> Modified:
>>> llvm/trunk/test/Analysis/BasicAA/2006-03-03-BadArraySubscript.ll
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/BasicAA/2006-03-03-BadArraySubscript.ll?rev=198290&r1=198289&r2=198290&view=diff
>>> 
>>> ==============================================================================
>>> 
>>> --- llvm/trunk/test/Analysis/BasicAA/2006-03-03-BadArraySubscript.ll
>>> (original)
>>> +++ llvm/trunk/test/Analysis/BasicAA/2006-03-03-BadArraySubscript.ll
>>> Wed Jan  1 21:31:36 2014
>>> @@ -1,4 +1,4 @@
>>> -; RUN: opt < %s -basicaa -aa-eval -disable-output 2>&1 | FileCheck %s
>>> +; RUN: opt < %s -domtree -basicaa -aa-eval -disable-output 2>&1 |
>>> FileCheck %s
>> 
>> Adding -domtree to all these tests makes me very sad.
>> 
>> Nick
>> 
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>