Do not verify MachimeDominatorTree if it is not calculated

If dominator tree is not calculated or is invalidated, set corresponding
pointer in the pass state to nullptr. Such pointer value will indicate
that operations with dominator tree are not allowed. In particular, it
allows to skip verification for such pass state. The dominator tree is
not calculated if the machine dominator pass was skipped, it occures in
the case of entities with linkage available_externally.

The change fixes some test fails observed when expensive checks
are enabled.

Differential Revision: https://reviews.llvm.org/D29280

llvm-svn: 296742

llvm/include/llvm/CodeGen/MachineDominators.h

@@ -21,6 +21,7 @@
 #include "llvm/CodeGen/MachineFunctionPass.h"
 #include "llvm/Support/GenericDomTree.h"
 #include "llvm/Support/GenericDomTreeConstruction.h"
+#include <memory>
 
 namespace llvm {
 
@@ -60,7 +61,7 @@ class MachineDominatorTree : public MachineFunctionPass {
   mutable SmallSet<MachineBasicBlock *, 32> NewBBs;
 
   /// The DominatorTreeBase that is used to compute a normal dominator tree
-  DominatorTreeBase<MachineBasicBlock>* DT;
+  std::unique_ptr<DominatorTreeBase<MachineBasicBlock>> DT;
 
   /// \brief Apply all the recorded critical edges to the DT.
   /// This updates the underlying DT information in a way that uses
@@ -74,9 +75,9 @@ public:
 
   MachineDominatorTree();
 
-  ~MachineDominatorTree() override;
-
   DominatorTreeBase<MachineBasicBlock> &getBase() {
+    if (!DT)
+      DT.reset(new DominatorTreeBase<MachineBasicBlock>(false));
     applySplitCriticalEdges();
     return *DT;
   }
@@ -244,21 +245,6 @@ public:
     CriticalEdgesToSplit.push_back({FromBB, ToBB, NewBB});
   }
 
-  /// \brief Returns *false* if the other dominator tree matches this dominator
-  /// tree.
-  inline bool compare(const MachineDominatorTree &Other) const {
-    const MachineDomTreeNode *R = getRootNode();
-    const MachineDomTreeNode *OtherR = Other.getRootNode();
-
-    if (!R || !OtherR || R->getBlock() != OtherR->getBlock())
-      return true;
-
-    if (DT->compare(*Other.DT))
-      return true;
-
-    return false;
-  }
-
   /// \brief Verify the correctness of the domtree by re-computing it.
   ///
   /// This should only be used for debugging as it aborts the program if the

llvm/lib/CodeGen/MachineDominators.cpp

@@ -49,32 +49,29 @@ void MachineDominatorTree::getAnalysisUsage(AnalysisUsage &AU) const {
 bool MachineDominatorTree::runOnMachineFunction(MachineFunction &F) {
   CriticalEdgesToSplit.clear();
   NewBBs.clear();
+  DT.reset(new DominatorTreeBase<MachineBasicBlock>(false));
   DT->recalculate(F);
-
   return false;
 }
 
 MachineDominatorTree::MachineDominatorTree()
     : MachineFunctionPass(ID) {
   initializeMachineDominatorTreePass(*PassRegistry::getPassRegistry());
-  DT = new DominatorTreeBase<MachineBasicBlock>(false);
-}
-
-MachineDominatorTree::~MachineDominatorTree() {
-  delete DT;
 }
 
 void MachineDominatorTree::releaseMemory() {
-  DT->releaseMemory();
+  CriticalEdgesToSplit.clear();
+  DT.reset(nullptr);
 }
 
 void MachineDominatorTree::verifyAnalysis() const {
-  if (VerifyMachineDomInfo)
+  if (DT && VerifyMachineDomInfo)
     verifyDomTree();
 }
 
 void MachineDominatorTree::print(raw_ostream &OS, const Module*) const {
-  DT->print(OS);
+  if (DT)
+    DT->print(OS);
 }
 
 void MachineDominatorTree::applySplitCriticalEdges() const {
@@ -143,15 +140,18 @@ void MachineDominatorTree::applySplitCriticalEdges() const {
 }
 
 void MachineDominatorTree::verifyDomTree() const {
+  if (!DT)
+    return;
   MachineFunction &F = *getRoot()->getParent();
 
-  MachineDominatorTree OtherDT;
-  OtherDT.DT->recalculate(F);
-  if (compare(OtherDT)) {
+  DominatorTreeBase<MachineBasicBlock> OtherDT(false);
+  OtherDT.recalculate(F);
+  if (getRootNode()->getBlock() != OtherDT.getRootNode()->getBlock() ||
+      DT->compare(OtherDT)) {
     errs() << "MachineDominatorTree is not up to date!\nComputed:\n";
-    print(errs(), nullptr);
+    DT->print(errs());
     errs() << "\nActual:\n";
-    OtherDT.print(errs(), nullptr);
+    OtherDT.print(errs());
     abort();
   }
 }

llvm/test/CodeGen/Generic/externally_available.ll

@@ -1,4 +1,4 @@
-; RUN: llc < %s | not grep test_
+; RUN: llc -verify-machine-dom-info < %s | not grep test_
 
 ; test_function should not be emitted to the .s file.
 define available_externally i32 @test_function() {