[llvm] r291927 - [SCEV] Limit recursion depth of constant evolving.

[Liao, Michael via llvm-commits]

Yes, I will address later as more code needs revising as I pointed out 
in the code review. That's short-term solution so far.

Thanks
- Michael

On 13/01/17 09:50 PM, Philip Reames wrote:
> Can this code be changed to use an iterative algorithm instead of a
> recursive one easily?  If so, doing that would be strongly preferred.
>
> Philip
>
>
> On 01/13/2017 10:28 AM, Michael Liao via llvm-commits wrote:
>> Author: hliao
>> Date: Fri Jan 13 12:28:30 2017
>> New Revision: 291927
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=291927&view=rev
>> Log:
>> [SCEV] Limit recursion depth of constant evolving.
>>
>> - For a loop body with VERY complicated exit condition evaluation, constant
>>    evolving may run out of stack on platforms such as Windows. Need to limit the
>>    recursion depth.
>>
>> Differential Revision: https://reviews.llvm.org/D28629
>>
>>
>> Modified:
>>      llvm/trunk/lib/Analysis/ScalarEvolution.cpp
>>
>> Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=291927&r1=291926&r2=291927&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
>> +++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Fri Jan 13 12:28:30 2017
>> @@ -132,6 +132,10 @@ static cl::opt<unsigned>
>>                       cl::desc("Maximum depth of recursive compare complexity"),
>>                       cl::init(32));
>>
>> +static cl::opt<unsigned> MaxConstantEvolvingDepth(
>> +    "scalar-evolution-max-constant-evolving-depth", cl::Hidden,
>> +    cl::desc("Maximum depth of recursive constant evolving"), cl::init(32));
>> +
>>   //===----------------------------------------------------------------------===//
>>   //                           SCEV class definitions
>>   //===----------------------------------------------------------------------===//
>> @@ -6403,7 +6407,10 @@ static bool canConstantEvolve(Instructio
>>   /// recursing through each instruction operand until reaching a loop header phi.
>>   static PHINode *
>>   getConstantEvolvingPHIOperands(Instruction *UseInst, const Loop *L,
>> -                               DenseMap<Instruction *, PHINode *> &PHIMap) {
>> +                               DenseMap<Instruction *, PHINode *> &PHIMap,
>> +                               unsigned Depth) {
>> +  if (Depth > MaxConstantEvolvingDepth)
>> +    return nullptr;
>>
>>     // Otherwise, we can evaluate this instruction if all of its operands are
>>     // constant or derived from a PHI node themselves.
>> @@ -6423,7 +6430,7 @@ getConstantEvolvingPHIOperands(Instructi
>>       if (!P) {
>>         // Recurse and memoize the results, whether a phi is found or not.
>>         // This recursive call invalidates pointers into PHIMap.
>> -      P = getConstantEvolvingPHIOperands(OpInst, L, PHIMap);
>> +      P = getConstantEvolvingPHIOperands(OpInst, L, PHIMap, Depth + 1);
>>         PHIMap[OpInst] = P;
>>       }
>>       if (!P)
>> @@ -6450,7 +6457,7 @@ static PHINode *getConstantEvolvingPHI(V
>>
>>     // Record non-constant instructions contained by the loop.
>>     DenseMap<Instruction *, PHINode *> PHIMap;
>> -  return getConstantEvolvingPHIOperands(I, L, PHIMap);
>> +  return getConstantEvolvingPHIOperands(I, L, PHIMap, 0);
>>   }
>>
>>   /// EvaluateExpression - Given an expression that passes the
>>
>>
>> _______________________________________________
>> llvm-commits mailing list
>> llvm-commits at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits
>
>