1 files changed, 26 insertions, 13 deletions

diff --git a/llvm/lib/Transforms/Scalar/CallSiteSplitting.cpp b/llvm/lib/Transforms/Scalar/CallSiteSplitting.cpp
index fc7450a7d9c..2be41605c98 100644
--- a/llvm/lib/Transforms/Scalar/CallSiteSplitting.cpp
+++ b/llvm/lib/Transforms/Scalar/CallSiteSplitting.cpp
@@ -149,14 +149,14 @@ static void recordCondition(CallSite CS, BasicBlock *From, BasicBlock *To,
 
 /// Record ICmp conditions relevant to any argument in CS following Pred's
 /// single predecessors. If there are conflicting conditions along a path, like
-/// x == 1 and x == 0, the first condition will be used.
+/// x == 1 and x == 0, the first condition will be used. We stop once we reach
+/// an edge to StopAt.
 static void recordConditions(CallSite CS, BasicBlock *Pred,
-                             ConditionsTy &Conditions) {
-  recordCondition(CS, Pred, CS.getInstruction()->getParent(), Conditions);
+                             ConditionsTy &Conditions, BasicBlock *StopAt) {
   BasicBlock *From = Pred;
   BasicBlock *To = Pred;
   SmallPtrSet<BasicBlock *, 4> Visited;
-  while (!Visited.count(From->getSinglePredecessor()) &&
+  while (To != StopAt && !Visited.count(From->getSinglePredecessor()) &&
          (From = From->getSinglePredecessor())) {
     recordCondition(CS, From, To, Conditions);
     Visited.insert(From);
@@ -453,15 +453,27 @@ static PredsWithCondsTy shouldSplitOnPHIPredicatedArgument(CallSite CS) {
 // Checks if any of the arguments in CS are predicated in a predecessor and
 // returns a list of predecessors with the conditions that hold on their edges
 // to CS.
-static PredsWithCondsTy shouldSplitOnPredicatedArgument(CallSite CS) {
+static PredsWithCondsTy shouldSplitOnPredicatedArgument(CallSite CS,
+                                                        DomTreeUpdater &DTU) {
   auto Preds = getTwoPredecessors(CS.getInstruction()->getParent());
   if (Preds[0] == Preds[1])
     return {};
 
+  // We can stop recording conditions once we reached the immediate dominator
+  // for the block containing the call site. Conditions in predecessors of the
+  // that node will be the same for all paths to the call site and splitting
+  // is not beneficial.
+  assert(DTU.hasDomTree() && "We need a DTU with a valid DT!");
+  auto *CSDTNode = DTU.getDomTree().getNode(CS.getInstruction()->getParent());
+  BasicBlock *StopAt = CSDTNode ? CSDTNode->getIDom()->getBlock() : nullptr;
+
   SmallVector<std::pair<BasicBlock *, ConditionsTy>, 2> PredsCS;
   for (auto *Pred : make_range(Preds.rbegin(), Preds.rend())) {
     ConditionsTy Conditions;
-    recordConditions(CS, Pred, Conditions);
+    // Record condition on edge BB(CS) <- Pred
+    recordCondition(CS, Pred, CS.getInstruction()->getParent(), Conditions);
+    // Record conditions following Pred's single predecessors.
+    recordConditions(CS, Pred, Conditions, StopAt);
     PredsCS.push_back({Pred, Conditions});
   }
 
@@ -479,7 +491,7 @@ static bool tryToSplitCallSite(CallSite CS, TargetTransformInfo &TTI,
   if (!CS.arg_size() || !canSplitCallSite(CS, TTI))
     return false;
 
-  auto PredsWithConds = shouldSplitOnPredicatedArgument(CS);
+  auto PredsWithConds = shouldSplitOnPredicatedArgument(CS, DTU);
   if (PredsWithConds.empty())
     PredsWithConds = shouldSplitOnPHIPredicatedArgument(CS);
   if (PredsWithConds.empty())
@@ -490,9 +502,9 @@ static bool tryToSplitCallSite(CallSite CS, TargetTransformInfo &TTI,
 }
 
 static bool doCallSiteSplitting(Function &F, TargetLibraryInfo &TLI,
-                                TargetTransformInfo &TTI, DominatorTree *DT) {
+                                TargetTransformInfo &TTI, DominatorTree &DT) {
 
-  DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy);
+  DomTreeUpdater DTU(&DT, DomTreeUpdater::UpdateStrategy::Lazy);
   bool Changed = false;
   for (Function::iterator BI = F.begin(), BE = F.end(); BI != BE;) {
     BasicBlock &BB = *BI++;
@@ -537,6 +549,7 @@ struct CallSiteSplittingLegacyPass : public FunctionPass {
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.addRequired<TargetLibraryInfoWrapperPass>();
     AU.addRequired<TargetTransformInfoWrapperPass>();
+    AU.addRequired<DominatorTreeWrapperPass>();
     AU.addPreserved<DominatorTreeWrapperPass>();
     FunctionPass::getAnalysisUsage(AU);
   }
@@ -547,9 +560,8 @@ struct CallSiteSplittingLegacyPass : public FunctionPass {
 
     auto &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
     auto &TTI = getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
-    auto *DTWP = getAnalysisIfAvailable<DominatorTreeWrapperPass>();
-    return doCallSiteSplitting(F, TLI, TTI,
-                               DTWP ? &DTWP->getDomTree() : nullptr);
+    auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+    return doCallSiteSplitting(F, TLI, TTI, DT);
   }
 };
 } // namespace
@@ -559,6 +571,7 @@ INITIALIZE_PASS_BEGIN(CallSiteSplittingLegacyPass, "callsite-splitting",
                       "Call-site splitting", false, false)
 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
 INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
 INITIALIZE_PASS_END(CallSiteSplittingLegacyPass, "callsite-splitting",
                     "Call-site splitting", false, false)
 FunctionPass *llvm::createCallSiteSplittingPass() {
@@ -569,7 +582,7 @@ PreservedAnalyses CallSiteSplittingPass::run(Function &F,
                                              FunctionAnalysisManager &AM) {
   auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
   auto &TTI = AM.getResult<TargetIRAnalysis>(F);
-  auto *DT = AM.getCachedResult<DominatorTreeAnalysis>(F);
+  auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
 
   if (!doCallSiteSplitting(F, TLI, TTI, DT))
     return PreservedAnalyses::all();