[CallSiteSplitting] Only record conditions up to the IDom(call site).

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.

This patch makes CallSiteSplitting dependent on the DT anlysis. because
the immediate dominators seem to be the easiest way of finding the node
to stop at.

I had to update some exiting tests, because they were checking for
conditions that were true/false on all paths to the call site. Those
should now be handled by instcombine/ipsccp.

Reviewers: davide, junbuml

Reviewed By: junbuml

Differential Revision: https://reviews.llvm.org/D44627

llvm-svn: 346483

1 files changed, 38 insertions, 15 deletions

diff --git a/llvm/lib/Transforms/Scalar/CallSiteSplitting.cpp b/llvm/lib/Transforms/Scalar/CallSiteSplitting.cpp
index b9e8e3424cc..208dd5a5a83 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);
@@ -302,7 +302,7 @@ static void copyMustTailReturn(BasicBlock *SplitBB, Instruction *CI,
 static void splitCallSite(
     CallSite CS,
     const SmallVectorImpl<std::pair<BasicBlock *, ConditionsTy>> &Preds,
-    DominatorTree *DT) {
+    DominatorTree &DT) {
   Instruction *Instr = CS.getInstruction();
   BasicBlock *TailBB = Instr->getParent();
   bool IsMustTailCall = CS.isMustTailCall();
@@ -327,7 +327,7 @@ static void splitCallSite(
     BasicBlock *PredBB = Preds[i].first;
     BasicBlock *SplitBlock = DuplicateInstructionsInSplitBetween(
         TailBB, PredBB, &*std::next(Instr->getIterator()), ValueToValueMaps[i],
-        DT);
+        &DT);
     assert(SplitBlock && "Unexpected new basic block split.");
 
     Instruction *NewCI =
@@ -438,7 +438,7 @@ static bool isPredicatedOnPHI(CallSite CS) {
   return false;
 }
 
-static bool tryToSplitOnPHIPredicatedArgument(CallSite CS, DominatorTree *DT) {
+static bool tryToSplitOnPHIPredicatedArgument(CallSite CS, DominatorTree &DT) {
   if (!isPredicatedOnPHI(CS))
     return false;
 
@@ -449,15 +449,25 @@ static bool tryToSplitOnPHIPredicatedArgument(CallSite CS, DominatorTree *DT) {
   return true;
 }
 
-static bool tryToSplitOnPredicatedArgument(CallSite CS, DominatorTree *DT) {
+static bool tryToSplitOnPredicatedArgument(CallSite CS, DominatorTree &DT) {
   auto Preds = getTwoPredecessors(CS.getInstruction()->getParent());
   if (Preds[0] == Preds[1])
     return false;
 
+  // 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.
+  auto *CSDTNode = DT.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 followng Pred's single predecessors.
+    recordConditions(CS, Pred, Conditions, StopAt);
     PredsCS.push_back({Pred, Conditions});
   }
 
@@ -466,12 +476,24 @@ static bool tryToSplitOnPredicatedArgument(CallSite CS, DominatorTree *DT) {
       }))
     return false;
 
+  // Record common conditions starting from StopAt. Those conditions hold for
+  // all paths to CS. Adding them gives the inliner a better chance at inlining
+  // CS.
+  ConditionsTy CommonConditions;
+  if (StopAt)
+    recordConditions(CS, StopAt, CommonConditions, nullptr);
+  if (!CommonConditions.empty())
+    for (auto &Pred : PredsCS) {
+      Pred.second.insert(Pred.second.end(), CommonConditions.begin(),
+                         CommonConditions.end());
+    }
+
   splitCallSite(CS, PredsCS, DT);
   return true;
 }
 
 static bool tryToSplitCallSite(CallSite CS, TargetTransformInfo &TTI,
-                               DominatorTree *DT) {
+                               DominatorTree &DT) {
   if (!CS.arg_size() || !canSplitCallSite(CS, TTI))
     return false;
   return tryToSplitOnPredicatedArgument(CS, DT) ||
@@ -479,7 +501,7 @@ static bool tryToSplitCallSite(CallSite CS, TargetTransformInfo &TTI,
 }
 
 static bool doCallSiteSplitting(Function &F, TargetLibraryInfo &TLI,
-                                TargetTransformInfo &TTI, DominatorTree *DT) {
+                                TargetTransformInfo &TTI, DominatorTree &DT) {
   bool Changed = false;
   for (Function::iterator BI = F.begin(), BE = F.end(); BI != BE;) {
     BasicBlock &BB = *BI++;
@@ -524,6 +546,7 @@ 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);
   }
@@ -534,9 +557,8 @@ 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
@@ -546,6 +568,7 @@ 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() {
@@ -556,7 +579,7 @@ 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();