Commit 3318c1d6 authored by Tom Stellard's avatar Tom Stellard
Browse files

Merging r326404: 

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r326404 | rnk | 2018-02-28 17:19:18 -0800 (Wed, 28 Feb 2018) | 14 lines

[IPSCCP] do not break musttail invariant (PR36485)

Do not replace results of `musttail` calls with a constant if the
call itself can't be removed.

Do not zap returns of `musttail` callees, if the call site can't be
removed and replaced with a constant.

Do not zap returns of `musttail`-calling blocks, this breaks
invariant too.

Patch by Fedor Indutny

Differential Revision: https://reviews.llvm.org/D43695
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llvm-svn: 329855
parent 8f8ecdf7

llvm/lib/Transforms/Scalar/SCCP.cpp

+55 −1
Original line number Diff line number Diff line
@@ -223,6 +223,10 @@ class SCCPSolver : public InstVisitor<SCCPSolver> { 
  /// represented here for efficient lookup.

  SmallPtrSet<Function *, 16> MRVFunctionsTracked;



  /// MustTailFunctions - Each function here is a callee of non-removable

  /// musttail call site.

  SmallPtrSet<Function *, 16> MustTailCallees;



  /// TrackingIncomingArguments - This is the set of functions for whose

  /// arguments we make optimistic assumptions about and try to prove as

  /// constants.
@@ -289,6 +293,18 @@ public: 
      TrackedRetVals.insert(std::make_pair(F, LatticeVal()));

  }



  /// AddMustTailCallee - If the SCCP solver finds that this function is called

  /// from non-removable musttail call site.

  void AddMustTailCallee(Function *F) {

    MustTailCallees.insert(F);

  }



  /// Returns true if the given function is called from non-removable musttail

  /// call site.

  bool isMustTailCallee(Function *F) {

    return MustTailCallees.count(F);

  }



  void AddArgumentTrackedFunction(Function *F) {

    TrackingIncomingArguments.insert(F);

  }
@@ -358,6 +374,12 @@ public: 
    return MRVFunctionsTracked;

  }



  /// getMustTailCallees - Get the set of functions which are called

  /// from non-removable musttail call sites.

  const SmallPtrSet<Function *, 16> getMustTailCallees() {

    return MustTailCallees;

  }



  /// markOverdefined - Mark the specified value overdefined.  This

  /// works with both scalars and structs.

  void markOverdefined(Value *V) {
@@ -1672,6 +1694,23 @@ static bool tryToReplaceWithConstant(SCCPSolver &Solver, Value *V) { 
          IV.isConstant() ? IV.getConstant() : UndefValue::get(V->getType());

  }

  assert(Const && "Constant is nullptr here!");



  // Replacing `musttail` instructions with constant breaks `musttail` invariant

  // unless the call itself can be removed

  CallInst *CI = dyn_cast<CallInst>(V);

  if (CI && CI->isMustTailCall() && !isInstructionTriviallyDead(CI)) {

    CallSite CS(CI);

    Function *F = CS.getCalledFunction();



    // Don't zap returns of the callee

    if (F)

      Solver.AddMustTailCallee(F);



    DEBUG(dbgs() << "  Can\'t treat the result of musttail call : " << *CI

                 << " as a constant\n");

    return false;

  }



  DEBUG(dbgs() << "  Constant: " << *Const << " = " << *V << '\n');



  // Replaces all of the uses of a variable with uses of the constant.
@@ -1802,11 +1841,26 @@ static void findReturnsToZap(Function &F, 
  if (!Solver.isArgumentTrackedFunction(&F))

    return;



  for (BasicBlock &BB : F)

  // There is a non-removable musttail call site of this function. Zapping

  // returns is not allowed.

  if (Solver.isMustTailCallee(&F)) {

    DEBUG(dbgs() << "Can't zap returns of the function : " << F.getName()

                 << " due to present musttail call of it\n");

    return;

  }



  for (BasicBlock &BB : F) {

    if (CallInst *CI = BB.getTerminatingMustTailCall()) {

      DEBUG(dbgs() << "Can't zap return of the block due to present "

                   << "musttail call : " << *CI << "\n");

      return;

    }



    if (auto *RI = dyn_cast<ReturnInst>(BB.getTerminator()))

      if (!isa<UndefValue>(RI->getOperand(0)))

        ReturnsToZap.push_back(RI);

  }

}



static bool runIPSCCP(Module &M, const DataLayout &DL,

                      const TargetLibraryInfo *TLI) {