[llvm] r291927 - [SCEV] Limit recursion depth of constant evolving.
Philip Reames via llvm-commits
llvm-commits at lists.llvm.org
Fri Jan 13 21:50:04 PST 2017
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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