[SimpleLoopUnswitch] Implement handling of prof branch_weights metadata for SwitchInst

Differential Revision: https://reviews.llvm.org/D60606

llvm-svn: 364734

1 files changed, 39 insertions, 17 deletions

diff --git a/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp b/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
index 9fba159..cb78240 100644
--- a/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
+++ b/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
@@ -594,11 +594,13 @@ static bool unswitchTrivialSwitch(Loop &L, SwitchInst &SI, DominatorTree &DT,
       ExitCaseIndices.push_back(Case.getCaseIndex());
   }
   BasicBlock *DefaultExitBB = nullptr;
+  SwitchInstProfUpdateWrapper::CaseWeightOpt DefaultCaseWeight =
+      SwitchInstProfUpdateWrapper::getSuccessorWeight(SI, 0);
   if (!L.contains(SI.getDefaultDest()) &&
       areLoopExitPHIsLoopInvariant(L, *ParentBB, *SI.getDefaultDest()) &&
-      !isa<UnreachableInst>(SI.getDefaultDest()->getTerminator()))
+      !isa<UnreachableInst>(SI.getDefaultDest()->getTerminator())) {
     DefaultExitBB = SI.getDefaultDest();
-  else if (ExitCaseIndices.empty())
+  } else if (ExitCaseIndices.empty())
     return false;
 
   LLVM_DEBUG(dbgs() << "    unswitching trivial switch...\n");
@@ -622,8 +624,11 @@ static bool unswitchTrivialSwitch(Loop &L, SwitchInst &SI, DominatorTree &DT,
 
   // Store the exit cases into a separate data structure and remove them from
   // the switch.
-  SmallVector<std::pair<ConstantInt *, BasicBlock *>, 4> ExitCases;
+  SmallVector<std::tuple<ConstantInt *, BasicBlock *,
+                         SwitchInstProfUpdateWrapper::CaseWeightOpt>,
+              4> ExitCases;
   ExitCases.reserve(ExitCaseIndices.size());
+  SwitchInstProfUpdateWrapper SIW(SI);
   // We walk the case indices backwards so that we remove the last case first
   // and don't disrupt the earlier indices.
   for (unsigned Index : reverse(ExitCaseIndices)) {
@@ -633,9 +638,10 @@ static bool unswitchTrivialSwitch(Loop &L, SwitchInst &SI, DominatorTree &DT,
     if (!ExitL || ExitL->contains(OuterL))
       OuterL = ExitL;
     // Save the value of this case.
-    ExitCases.push_back({CaseI->getCaseValue(), CaseI->getCaseSuccessor()});
+    auto W = SIW.getSuccessorWeight(CaseI->getSuccessorIndex());
+    ExitCases.emplace_back(CaseI->getCaseValue(), CaseI->getCaseSuccessor(), W);
     // Delete the unswitched cases.
-    SI.removeCase(CaseI);
+    SIW.removeCase(CaseI);
   }
 
   if (SE) {
@@ -673,6 +679,7 @@ static bool unswitchTrivialSwitch(Loop &L, SwitchInst &SI, DominatorTree &DT,
 
   // Now add the unswitched switch.
   auto *NewSI = SwitchInst::Create(LoopCond, NewPH, ExitCases.size(), OldPH);
+  SwitchInstProfUpdateWrapper NewSIW(*NewSI);
 
   // Rewrite the IR for the unswitched basic blocks. This requires two steps.
   // First, we split any exit blocks with remaining in-loop predecessors. Then
@@ -700,9 +707,9 @@ static bool unswitchTrivialSwitch(Loop &L, SwitchInst &SI, DominatorTree &DT,
   }
   // Note that we must use a reference in the for loop so that we update the
   // container.
-  for (auto &CasePair : reverse(ExitCases)) {
+  for (auto &ExitCase : reverse(ExitCases)) {
     // Grab a reference to the exit block in the pair so that we can update it.
-    BasicBlock *ExitBB = CasePair.second;
+    BasicBlock *ExitBB = std::get<1>(ExitCase);
 
     // If this case is the last edge into the exit block, we can simply reuse it
     // as it will no longer be a loop exit. No mapping necessary.
@@ -724,27 +731,39 @@ static bool unswitchTrivialSwitch(Loop &L, SwitchInst &SI, DominatorTree &DT,
                                                 /*FullUnswitch*/ true);
     }
     // Update the case pair to point to the split block.
-    CasePair.second = SplitExitBB;
+    std::get<1>(ExitCase) = SplitExitBB;
   }
 
   // Now add the unswitched cases. We do this in reverse order as we built them
   // in reverse order.
-  for (auto CasePair : reverse(ExitCases)) {
-    ConstantInt *CaseVal = CasePair.first;
-    BasicBlock *UnswitchedBB = CasePair.second;
+  for (auto &ExitCase : reverse(ExitCases)) {
+    ConstantInt *CaseVal = std::get<0>(ExitCase);
+    BasicBlock *UnswitchedBB = std::get<1>(ExitCase);
 
-    NewSI->addCase(CaseVal, UnswitchedBB);
+    NewSIW.addCase(CaseVal, UnswitchedBB, std::get<2>(ExitCase));
   }
 
   // If the default was unswitched, re-point it and add explicit cases for
   // entering the loop.
   if (DefaultExitBB) {
-    NewSI->setDefaultDest(DefaultExitBB);
+    NewSIW->setDefaultDest(DefaultExitBB);
+    NewSIW.setSuccessorWeight(0, DefaultCaseWeight);
 
     // We removed all the exit cases, so we just copy the cases to the
     // unswitched switch.
-    for (auto Case : SI.cases())
-      NewSI->addCase(Case.getCaseValue(), NewPH);
+    for (const auto &Case : SI.cases())
+      NewSIW.addCase(Case.getCaseValue(), NewPH,
+                     SIW.getSuccessorWeight(Case.getSuccessorIndex()));
+  } else if (DefaultCaseWeight) {
+    // We have to set branch weight of the default case.
+    uint64_t SW = *DefaultCaseWeight;
+    for (const auto &Case : SI.cases()) {
+      auto W = SIW.getSuccessorWeight(Case.getSuccessorIndex());
+      assert(W &&
+             "case weight must be defined as default case weight is defined");
+      SW += *W;
+    }
+    NewSIW.setSuccessorWeight(0, SW);
   }
 
   // If we ended up with a common successor for every path through the switch
@@ -769,7 +788,7 @@ static bool unswitchTrivialSwitch(Loop &L, SwitchInst &SI, DominatorTree &DT,
                                       /*KeepOneInputPHIs*/ true);
     }
     // Now nuke the switch and replace it with a direct branch.
-    SI.eraseFromParent();
+    SIW.eraseFromParent();
     BranchInst::Create(CommonSuccBB, BB);
   } else if (DefaultExitBB) {
     assert(SI.getNumCases() > 0 &&
@@ -779,8 +798,11 @@ static bool unswitchTrivialSwitch(Loop &L, SwitchInst &SI, DominatorTree &DT,
     // being simple and keeping the number of edges from this switch to
     // successors the same, and avoiding any PHI update complexity.
     auto LastCaseI = std::prev(SI.case_end());
+
     SI.setDefaultDest(LastCaseI->getCaseSuccessor());
-    SI.removeCase(LastCaseI);
+    SIW.setSuccessorWeight(
+        0, SIW.getSuccessorWeight(LastCaseI->getSuccessorIndex()));
+    SIW.removeCase(LastCaseI);
   }
 
   // Walk the unswitched exit blocks and the unswitched split blocks and update