Use std::optional

Author: paperchalice

llvm/include/llvm/CodeGen/MachineDominators.h

@@ -24,6 +24,7 @@
 #include "llvm/Support/GenericDomTreeConstruction.h"
 #include <cassert>
 #include <memory>
+#include <optional>
 
 namespace llvm {
 class AnalysisUsage;
@@ -72,7 +73,6 @@ extern template bool Verify<MBBDomTree>(const MBBDomTree &DT,
 /// compute a normal dominator tree.
 ///
 class MachineDominatorTree : public DomTreeBase<MachineBasicBlock> {
-  friend class MachineDominatorTreeWrapperPass;
   /// Helper structure used to hold all the basic blocks
   /// involved in the split of a critical edge.
   struct CriticalEdge {
@@ -265,16 +265,17 @@ class MachineDominatorTree : public DomTreeBase<MachineBasicBlock> {
 
 /// \brief Analysis pass which computes a \c MachineDominatorTree.
 class MachineDominatorTreeWrapperPass : public MachineFunctionPass {
-  MachineDominatorTree DT;
-  bool IsDomTreeEmpty = true;
+  // MachineFunctionPass may verify the analysis result without running pass,
+  // e.g. when `F.hasAvailableExternallyLinkage` is true.
+  std::optional<MachineDominatorTree> DT;
 
 public:
   static char ID;
 
   MachineDominatorTreeWrapperPass();
 
-  MachineDominatorTree &getDomTree() { return DT; }
-  const MachineDominatorTree &getDomTree() const { return DT; }
+  MachineDominatorTree &getDomTree() { return *DT; }
+  const MachineDominatorTree &getDomTree() const { return *DT; }
 
   bool runOnMachineFunction(MachineFunction &MF) override;
 

llvm/lib/CodeGen/MachineDominators.cpp

@@ -67,35 +67,31 @@ MachineDominatorTreeWrapperPass::MachineDominatorTreeWrapperPass()
       *PassRegistry::getPassRegistry());
 }
 
-char &llvm::MachineDominatorsID = MachineDominatorTreeWrapperPass::ID;
-
-bool MachineDominatorTreeWrapperPass::runOnMachineFunction(MachineFunction &F) {
-  IsDomTreeEmpty = false;
-  DT.calculate(F);
-  return false;
-}
-
 void MachineDominatorTree::calculate(MachineFunction &F) {
   CriticalEdgesToSplit.clear();
   NewBBs.clear();
   recalculate(F);
 }
 
-void MachineDominatorTreeWrapperPass::releaseMemory() {
-  DT.CriticalEdgesToSplit.clear();
-  DT.reset();
-  IsDomTreeEmpty = true;
+char &llvm::MachineDominatorsID = MachineDominatorTreeWrapperPass::ID;
+
+bool MachineDominatorTreeWrapperPass::runOnMachineFunction(MachineFunction &F) {
+  DT = MachineDominatorTree(F);
+  return false;
 }
 
+void MachineDominatorTreeWrapperPass::releaseMemory() { DT.reset(); }
+
 void MachineDominatorTreeWrapperPass::verifyAnalysis() const {
-  if (VerifyMachineDomInfo && !IsDomTreeEmpty)
-    if (!DT.verify(MachineDominatorTree::VerificationLevel::Basic))
+  if (VerifyMachineDomInfo && DT)
+    if (!DT->verify(MachineDominatorTree::VerificationLevel::Basic))
       report_fatal_error("MachineDominatorTree verification failed!");
 }
 
 void MachineDominatorTreeWrapperPass::print(raw_ostream &OS,
                                             const Module *) const {
-  DT.print(OS);
+  if (DT)
+    DT->print(OS);
 }
 
 void MachineDominatorTree::applySplitCriticalEdges() const {
@@ -148,7 +144,6 @@ void MachineDominatorTree::applySplitCriticalEdges() const {
 
   // Now, update DT with the collected dominance properties info.
   Idx = 0;
-  dbgs() << "critical Edge to split: " << CriticalEdgesToSplit.size();
   for (CriticalEdge &Edge : CriticalEdgesToSplit) {
     // We know FromBB dominates NewBB.
     MachineDomTreeNode *NewDTNode =