1 files changed, 492 insertions, 0 deletions
diff --git a/lib/Transforms/Scalar/CallSiteSplitting.cpp b/lib/Transforms/Scalar/CallSiteSplitting.cpp
new file mode 100644
index 00000000000..b70ed8d7d4c
--- /dev/null
+++ b/lib/Transforms/Scalar/CallSiteSplitting.cpp
@@ -0,0 +1,492 @@
+//===- CallSiteSplitting.cpp ----------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements a transformation that tries to split a call-site to pass
+// more constrained arguments if its argument is predicated in the control flow
+// so that we can expose better context to the later passes (e.g, inliner, jump
+// threading, or IPA-CP based function cloning, etc.).
+// As of now we support two cases :
+//
+// 1) If a call site is dominated by an OR condition and if any of its arguments
+// are predicated on this OR condition, try to split the condition with more
+// constrained arguments. For example, in the code below, we try to split the
+// call site since we can predicate the argument(ptr) based on the OR condition.
+//
+// Split from :
+//   if (!ptr || c)
+//     callee(ptr);
+// to :
+//   if (!ptr)
+//     callee(null)         // set the known constant value
+//   else if (c)
+//     callee(nonnull ptr)  // set non-null attribute in the argument
+//
+// 2) We can also split a call-site based on constant incoming values of a PHI
+// For example,
+// from :
+//   Header:
+//    %c = icmp eq i32 %i1, %i2
+//    br i1 %c, label %Tail, label %TBB
+//   TBB:
+//    br label Tail%
+//   Tail:
+//    %p = phi i32 [ 0, %Header], [ 1, %TBB]
+//    call void @bar(i32 %p)
+// to
+//   Header:
+//    %c = icmp eq i32 %i1, %i2
+//    br i1 %c, label %Tail-split0, label %TBB
+//   TBB:
+//    br label %Tail-split1
+//   Tail-split0:
+//    call void @bar(i32 0)
+//    br label %Tail
+//   Tail-split1:
+//    call void @bar(i32 1)
+//    br label %Tail
+//   Tail:
+//    %p = phi i32 [ 0, %Tail-split0 ], [ 1, %Tail-split1 ]
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Scalar/CallSiteSplitting.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/TargetLibraryInfo.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/PatternMatch.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "llvm/Transforms/Utils/Local.h"
+
+using namespace llvm;
+using namespace PatternMatch;
+
+#define DEBUG_TYPE "callsite-splitting"
+
+STATISTIC(NumCallSiteSplit, "Number of call-site split");
+
+static void addNonNullAttribute(Instruction *CallI, Instruction *&NewCallI,
+                                Value *Op) {
+  if (!NewCallI)
+    NewCallI = CallI->clone();
+  CallSite CS(NewCallI);
+  unsigned ArgNo = 0;
+  for (auto &I : CS.args()) {
+    if (&*I == Op)
+      CS.addParamAttr(ArgNo, Attribute::NonNull);
+    ++ArgNo;
+  }
+}
+
+static void setConstantInArgument(Instruction *CallI, Instruction *&NewCallI,
+                                  Value *Op, Constant *ConstValue) {
+  if (!NewCallI)
+    NewCallI = CallI->clone();
+  CallSite CS(NewCallI);
+  unsigned ArgNo = 0;
+  for (auto &I : CS.args()) {
+    if (&*I == Op)
+      CS.setArgument(ArgNo, ConstValue);
+    ++ArgNo;
+  }
+}
+
+static bool createCallSitesOnOrPredicatedArgument(
+    CallSite CS, Instruction *&NewCSTakenFromHeader,
+    Instruction *&NewCSTakenFromNextCond,
+    SmallVectorImpl<BranchInst *> &BranchInsts, BasicBlock *HeaderBB) {
+  assert(BranchInsts.size() <= 2 &&
+         "Unexpected number of blocks in the OR predicated condition");
+  Instruction *Instr = CS.getInstruction();
+  BasicBlock *CallSiteBB = Instr->getParent();
+  TerminatorInst *HeaderTI = HeaderBB->getTerminator();
+  bool IsCSInTakenPath = CallSiteBB == HeaderTI->getSuccessor(0);
+
+  for (unsigned I = 0, E = BranchInsts.size(); I != E; ++I) {
+    BranchInst *PBI = BranchInsts[I];
+    assert(isa<ICmpInst>(PBI->getCondition()) &&
+           "Unexpected condition in a conditional branch.");
+    ICmpInst *Cmp = cast<ICmpInst>(PBI->getCondition());
+    Value *Arg = Cmp->getOperand(0);
+    assert(isa<Constant>(Cmp->getOperand(1)) &&
+           "Expected op1 to be a constant.");
+    Constant *ConstVal = cast<Constant>(Cmp->getOperand(1));
+    CmpInst::Predicate Pred = Cmp->getPredicate();
+
+    if (PBI->getParent() == HeaderBB) {
+      Instruction *&CallTakenFromHeader =
+          IsCSInTakenPath ? NewCSTakenFromHeader : NewCSTakenFromNextCond;
+      Instruction *&CallUntakenFromHeader =
+          IsCSInTakenPath ? NewCSTakenFromNextCond : NewCSTakenFromHeader;
+
+      assert((Pred == ICmpInst::ICMP_EQ || Pred == ICmpInst::ICMP_NE) &&
+             "Unexpected predicate in an OR condition");
+
+      // Set the constant value for agruments in the call predicated based on
+      // the OR condition.
+      Instruction *&CallToSetConst = Pred == ICmpInst::ICMP_EQ
+                                         ? CallTakenFromHeader
+                                         : CallUntakenFromHeader;
+      setConstantInArgument(Instr, CallToSetConst, Arg, ConstVal);
+
+      // Add the NonNull attribute if compared with the null pointer.
+      if (ConstVal->getType()->isPointerTy() && ConstVal->isNullValue()) {
+        Instruction *&CallToSetAttr = Pred == ICmpInst::ICMP_EQ
+                                          ? CallUntakenFromHeader
+                                          : CallTakenFromHeader;
+        addNonNullAttribute(Instr, CallToSetAttr, Arg);
+      }
+      continue;
+    }
+
+    if (Pred == ICmpInst::ICMP_EQ) {
+      if (PBI->getSuccessor(0) == Instr->getParent()) {
+        // Set the constant value for the call taken from the second block in
+        // the OR condition.
+        setConstantInArgument(Instr, NewCSTakenFromNextCond, Arg, ConstVal);
+      } else {
+        // Add the NonNull attribute if compared with the null pointer for the
+        // call taken from the second block in the OR condition.
+        if (ConstVal->getType()->isPointerTy() && ConstVal->isNullValue())
+          addNonNullAttribute(Instr, NewCSTakenFromNextCond, Arg);
+      }
+    } else {
+      if (PBI->getSuccessor(0) == Instr->getParent()) {
+        // Add the NonNull attribute if compared with the null pointer for the
+        // call taken from the second block in the OR condition.
+        if (ConstVal->getType()->isPointerTy() && ConstVal->isNullValue())
+          addNonNullAttribute(Instr, NewCSTakenFromNextCond, Arg);
+      } else if (Pred == ICmpInst::ICMP_NE) {
+        // Set the constant value for the call in the untaken path from the
+        // header block.
+        setConstantInArgument(Instr, NewCSTakenFromNextCond, Arg, ConstVal);
+      } else
+        llvm_unreachable("Unexpected condition");
+    }
+  }
+  return NewCSTakenFromHeader || NewCSTakenFromNextCond;
+}
+
+static bool canSplitCallSite(CallSite CS) {
+  // FIXME: As of now we handle only CallInst. InvokeInst could be handled
+  // without too much effort.
+  Instruction *Instr = CS.getInstruction();
+  if (!isa<CallInst>(Instr))
+    return false;
+
+  // Allow splitting a call-site only when there is no instruction before the
+  // call-site in the basic block. Based on this constraint, we only clone the
+  // call instruction, and we do not move a call-site across any other
+  // instruction.
+  BasicBlock *CallSiteBB = Instr->getParent();
+  if (Instr != CallSiteBB->getFirstNonPHI())
+    return false;
+
+  pred_iterator PII = pred_begin(CallSiteBB);
+  pred_iterator PIE = pred_end(CallSiteBB);
+  unsigned NumPreds = std::distance(PII, PIE);
+
+  // Allow only one extra call-site. No more than two from one call-site.
+  if (NumPreds != 2)
+    return false;
+
+  // Cannot split an edge from an IndirectBrInst.
+  BasicBlock *Preds[2] = {*PII++, *PII};
+  if (isa<IndirectBrInst>(Preds[0]->getTerminator()) ||
+      isa<IndirectBrInst>(Preds[1]->getTerminator()))
+    return false;
+
+  return CallSiteBB->canSplitPredecessors();
+}
+
+/// Return true if the CS is split into its new predecessors which are directly
+/// hooked to each of its orignial predecessors pointed by PredBB1 and PredBB2.
+/// Note that PredBB1 and PredBB2 are decided in findPredicatedArgument(),
+/// especially for the OR predicated case where PredBB1 will point the header,
+/// and PredBB2 will point the the second compare block. CallInst1 and CallInst2
+/// will be the new call-sites placed in the new predecessors split for PredBB1
+/// and PredBB2, repectively. Therefore, CallInst1 will be the call-site placed
+/// between Header and Tail, and CallInst2 will be the call-site between TBB and
+/// Tail. For example, in the IR below with an OR condition, the call-site can
+/// be split
+///
+/// from :
+///
+///   Header:
+///     %c = icmp eq i32* %a, null
+///     br i1 %c %Tail, %TBB
+///   TBB:
+///     %c2 = icmp eq i32* %b, null
+///     br i1 %c %Tail, %End
+///   Tail:
+///     %ca = call i1  @callee (i32* %a, i32* %b)
+///
+///  to :
+///
+///   Header:                          // PredBB1 is Header
+///     %c = icmp eq i32* %a, null
+///     br i1 %c %Tail-split1, %TBB
+///   TBB:                             // PredBB2 is TBB
+///     %c2 = icmp eq i32* %b, null
+///     br i1 %c %Tail-split2, %End
+///   Tail-split1:
+///     %ca1 = call @callee (i32* null, i32* %b)         // CallInst1
+///    br %Tail
+///   Tail-split2:
+///     %ca2 = call @callee (i32* nonnull %a, i32* null) // CallInst2
+///    br %Tail
+///   Tail:
+///    %p = phi i1 [%ca1, %Tail-split1],[%ca2, %Tail-split2]
+///
+/// Note that for an OR predicated case, CallInst1 and CallInst2 should be
+/// created with more constrained arguments in
+/// createCallSitesOnOrPredicatedArgument().
+static void splitCallSite(CallSite CS, BasicBlock *PredBB1, BasicBlock *PredBB2,
+                          Instruction *CallInst1, Instruction *CallInst2) {
+  Instruction *Instr = CS.getInstruction();
+  BasicBlock *TailBB = Instr->getParent();
+  assert(Instr == (TailBB->getFirstNonPHI()) && "Unexpected call-site");
+
+  BasicBlock *SplitBlock1 =
+      SplitBlockPredecessors(TailBB, PredBB1, ".predBB1.split");
+  BasicBlock *SplitBlock2 =
+      SplitBlockPredecessors(TailBB, PredBB2, ".predBB2.split");
+
+  assert((SplitBlock1 && SplitBlock2) && "Unexpected new basic block split.");
+
+  if (!CallInst1)
+    CallInst1 = Instr->clone();
+  if (!CallInst2)
+    CallInst2 = Instr->clone();
+
+  CallInst1->insertBefore(&*SplitBlock1->getFirstInsertionPt());
+  CallInst2->insertBefore(&*SplitBlock2->getFirstInsertionPt());
+
+  CallSite CS1(CallInst1);
+  CallSite CS2(CallInst2);
+
+  // Handle PHIs used as arguments in the call-site.
+  for (auto &PI : *TailBB) {
+    PHINode *PN = dyn_cast<PHINode>(&PI);
+    if (!PN)
+      break;
+    unsigned ArgNo = 0;
+    for (auto &CI : CS.args()) {
+      if (&*CI == PN) {
+        CS1.setArgument(ArgNo, PN->getIncomingValueForBlock(SplitBlock1));
+        CS2.setArgument(ArgNo, PN->getIncomingValueForBlock(SplitBlock2));
+      }
+      ++ArgNo;
+    }
+  }
+
+  // Replace users of the original call with a PHI mering call-sites split.
+  if (Instr->getNumUses()) {
+    PHINode *PN = PHINode::Create(Instr->getType(), 2, "phi.call", Instr);
+    PN->addIncoming(CallInst1, SplitBlock1);
+    PN->addIncoming(CallInst2, SplitBlock2);
+    Instr->replaceAllUsesWith(PN);
+  }
+  DEBUG(dbgs() << "split call-site : " << *Instr << " into \n");
+  DEBUG(dbgs() << "    " << *CallInst1 << " in " << SplitBlock1->getName()
+               << "\n");
+  DEBUG(dbgs() << "    " << *CallInst2 << " in " << SplitBlock2->getName()
+               << "\n");
+  Instr->eraseFromParent();
+  NumCallSiteSplit++;
+}
+
+static bool isCondRelevantToAnyCallArgument(ICmpInst *Cmp, CallSite CS) {
+  assert(isa<Constant>(Cmp->getOperand(1)) && "Expected a constant operand.");
+  Value *Op0 = Cmp->getOperand(0);
+  unsigned ArgNo = 0;
+  for (CallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end(); I != E;
+       ++I, ++ArgNo) {
+    // Don't consider constant or arguments that are already known non-null.
+    if (isa<Constant>(*I) || CS.paramHasAttr(ArgNo, Attribute::NonNull))
+      continue;
+
+    if (*I == Op0)
+      return true;
+  }
+  return false;
+}
+
+static void findOrCondRelevantToCallArgument(
+    CallSite CS, BasicBlock *PredBB, BasicBlock *OtherPredBB,
+    SmallVectorImpl<BranchInst *> &BranchInsts, BasicBlock *&HeaderBB) {
+  auto *PBI = dyn_cast<BranchInst>(PredBB->getTerminator());
+  if (!PBI || !PBI->isConditional())
+    return;
+
+  if (PBI->getSuccessor(0) == OtherPredBB ||
+      PBI->getSuccessor(1) == OtherPredBB)
+    if (PredBB == OtherPredBB->getSinglePredecessor()) {
+      assert(!HeaderBB && "Expect to find only a single header block");
+      HeaderBB = PredBB;
+    }
+
+  CmpInst::Predicate Pred;
+  Value *Cond = PBI->getCondition();
+  if (!match(Cond, m_ICmp(Pred, m_Value(), m_Constant())))
+    return;
+  ICmpInst *Cmp = cast<ICmpInst>(Cond);
+  if (Pred == ICmpInst::ICMP_EQ || Pred == ICmpInst::ICMP_NE)
+    if (isCondRelevantToAnyCallArgument(Cmp, CS))
+      BranchInsts.push_back(PBI);
+}
+
+// Return true if the call-site has an argument which is a PHI with only
+// constant incoming values.
+static bool isPredicatedOnPHI(CallSite CS) {
+  Instruction *Instr = CS.getInstruction();
+  BasicBlock *Parent = Instr->getParent();
+  if (Instr != Parent->getFirstNonPHI())
+    return false;
+
+  for (auto &BI : *Parent) {
+    if (PHINode *PN = dyn_cast<PHINode>(&BI)) {
+      for (auto &I : CS.args())
+        if (&*I == PN) {
+          assert(PN->getNumIncomingValues() == 2 &&
+                 "Unexpected number of incoming values");
+          if (PN->getIncomingBlock(0) == PN->getIncomingBlock(1))
+            return false;
+          if (PN->getIncomingValue(0) == PN->getIncomingValue(1))
+            continue;
+          if (isa<Constant>(PN->getIncomingValue(0)) &&
+              isa<Constant>(PN->getIncomingValue(1)))
+            return true;
+        }
+    }
+    break;
+  }
+  return false;
+}
+
+// Return true if an agument in CS is predicated on an 'or' condition.
+// Create new call-site with arguments constrained based on the OR condition.
+static bool findPredicatedOnOrCondition(CallSite CS, BasicBlock *PredBB1,
+                                        BasicBlock *PredBB2,
+                                        Instruction *&NewCallTakenFromHeader,
+                                        Instruction *&NewCallTakenFromNextCond,
+                                        BasicBlock *&HeaderBB) {
+  SmallVector<BranchInst *, 4> BranchInsts;
+  findOrCondRelevantToCallArgument(CS, PredBB1, PredBB2, BranchInsts, HeaderBB);
+  findOrCondRelevantToCallArgument(CS, PredBB2, PredBB1, BranchInsts, HeaderBB);
+  if (BranchInsts.empty() || !HeaderBB)
+    return false;
+
+  // If an OR condition is detected, try to create call sites with constrained
+  // arguments (e.g., NonNull attribute or constant value).
+  return createCallSitesOnOrPredicatedArgument(CS, NewCallTakenFromHeader,
+                                               NewCallTakenFromNextCond,
+                                               BranchInsts, HeaderBB);
+}
+
+static bool findPredicatedArgument(CallSite CS, Instruction *&CallInst1,
+                                   Instruction *&CallInst2,
+                                   BasicBlock *&PredBB1, BasicBlock *&PredBB2) {
+  BasicBlock *CallSiteBB = CS.getInstruction()->getParent();
+  pred_iterator PII = pred_begin(CallSiteBB);
+  pred_iterator PIE = pred_end(CallSiteBB);
+  assert(std::distance(PII, PIE) == 2 && "Expect only two predecessors.");
+  (void)PIE;
+  BasicBlock *Preds[2] = {*PII++, *PII};
+  BasicBlock *&HeaderBB = PredBB1;
+  if (!findPredicatedOnOrCondition(CS, Preds[0], Preds[1], CallInst1, CallInst2,
+                                   HeaderBB) &&
+      !isPredicatedOnPHI(CS))
+    return false;
+
+  if (!PredBB1)
+    PredBB1 = Preds[0];
+
+  PredBB2 = PredBB1 == Preds[0] ? Preds[1] : Preds[0];
+  return true;
+}
+
+static bool tryToSplitCallSite(CallSite CS) {
+  if (!CS.arg_size())
+    return false;
+
+  BasicBlock *PredBB1 = nullptr;
+  BasicBlock *PredBB2 = nullptr;
+  Instruction *CallInst1 = nullptr;
+  Instruction *CallInst2 = nullptr;
+  if (!canSplitCallSite(CS) ||
+      !findPredicatedArgument(CS, CallInst1, CallInst2, PredBB1, PredBB2)) {
+    assert(!CallInst1 && !CallInst2 && "Unexpected new call-sites cloned.");
+    return false;
+  }
+  splitCallSite(CS, PredBB1, PredBB2, CallInst1, CallInst2);
+  return true;
+}
+
+static bool doCallSiteSplitting(Function &F, TargetLibraryInfo &TLI) {
+  bool Changed = false;
+  for (Function::iterator BI = F.begin(), BE = F.end(); BI != BE;) {
+    BasicBlock &BB = *BI++;
+    for (BasicBlock::iterator II = BB.begin(), IE = BB.end(); II != IE;) {
+      Instruction *I = &*II++;
+      CallSite CS(cast<Value>(I));
+      if (!CS || isa<IntrinsicInst>(I) || isInstructionTriviallyDead(I, &TLI))
+        continue;
+
+      Function *Callee = CS.getCalledFunction();
+      if (!Callee || Callee->isDeclaration())
+        continue;
+      Changed |= tryToSplitCallSite(CS);
+    }
+  }
+  return Changed;
+}
+
+namespace {
+struct CallSiteSplittingLegacyPass : public FunctionPass {
+  static char ID;
+  CallSiteSplittingLegacyPass() : FunctionPass(ID) {
+    initializeCallSiteSplittingLegacyPassPass(*PassRegistry::getPassRegistry());
+  }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.addRequired<TargetLibraryInfoWrapperPass>();
+    FunctionPass::getAnalysisUsage(AU);
+  }
+
+  bool runOnFunction(Function &F) override {
+    if (skipFunction(F))
+      return false;
+
+    auto &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
+    return doCallSiteSplitting(F, TLI);
+  }
+};
+} // namespace
+
+char CallSiteSplittingLegacyPass::ID = 0;
+INITIALIZE_PASS_BEGIN(CallSiteSplittingLegacyPass, "callsite-splitting",
+                      "Call-site splitting", false, false)
+INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
+INITIALIZE_PASS_END(CallSiteSplittingLegacyPass, "callsite-splitting",
+                    "Call-site splitting", false, false)
+FunctionPass *llvm::createCallSiteSplittingPass() {
+  return new CallSiteSplittingLegacyPass();
+}
+
+PreservedAnalyses CallSiteSplittingPass::run(Function &F,
+                                             FunctionAnalysisManager &AM) {
+  auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
+
+  if (!doCallSiteSplitting(F, TLI))
+    return PreservedAnalyses::all();
+  PreservedAnalyses PA;
+  return PA;
+}