[llvm] r291927 - [SCEV] Limit recursion depth of constant evolving.
Liao, Michael via llvm-commits
llvm-commits at lists.llvm.org
Fri Jan 13 21:52:09 PST 2017
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
>>
>>
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