[CodeGen] Use optimized domtree for MachineFunction (#102107)

The dominator tree gained an optimization to use block numbers instead
of a DenseMap to store blocks. Given that machine basic blocks already
have numbers, expose these via appropriate GraphTraits. For debugging,
block number epochs are added to MachineFunction -- this greatly helps
in finding uses of block numbers after RenumberBlocks().

In a few cases where dominator trees are preserved across renumberings,
the dominator tree is updated to use the new numbers.

1 files changed, 5 insertions, 2 deletions

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp
index 70b91c2..c7001ef 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp
@@ -45,6 +45,8 @@ STATISTIC(NumCatchUnwindMismatches, "Number of catch unwind mismatches found");
 
 namespace {
 class WebAssemblyCFGStackify final : public MachineFunctionPass {
+  MachineDominatorTree *MDT;
+
   StringRef getPassName() const override { return "WebAssembly CFG Stackify"; }
 
   void getAnalysisUsage(AnalysisUsage &AU) const override {
@@ -252,7 +254,6 @@ void WebAssemblyCFGStackify::unregisterScope(MachineInstr *Begin) {
 void WebAssemblyCFGStackify::placeBlockMarker(MachineBasicBlock &MBB) {
   assert(!MBB.isEHPad());
   MachineFunction &MF = *MBB.getParent();
-  auto &MDT = getAnalysis<MachineDominatorTreeWrapperPass>().getDomTree();
   const auto &TII = *MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
   const auto &MFI = *MF.getInfo<WebAssemblyFunctionInfo>();
 
@@ -264,7 +265,7 @@ void WebAssemblyCFGStackify::placeBlockMarker(MachineBasicBlock &MBB) {
   int MBBNumber = MBB.getNumber();
   for (MachineBasicBlock *Pred : MBB.predecessors()) {
     if (Pred->getNumber() < MBBNumber) {
-      Header = Header ? MDT.findNearestCommonDominator(Header, Pred) : Pred;
+      Header = Header ? MDT->findNearestCommonDominator(Header, Pred) : Pred;
       if (explicitlyBranchesTo(Pred, &MBB))
         IsBranchedTo = true;
     }
@@ -1439,6 +1440,7 @@ void WebAssemblyCFGStackify::recalculateScopeTops(MachineFunction &MF) {
   // Renumber BBs and recalculate ScopeTop info because new BBs might have been
   // created and inserted during fixing unwind mismatches.
   MF.RenumberBlocks();
+  MDT->updateBlockNumbers();
   ScopeTops.clear();
   ScopeTops.resize(MF.getNumBlockIDs());
   for (auto &MBB : reverse(MF)) {
@@ -1741,6 +1743,7 @@ bool WebAssemblyCFGStackify::runOnMachineFunction(MachineFunction &MF) {
                        "********** Function: "
                     << MF.getName() << '\n');
   const MCAsmInfo *MCAI = MF.getTarget().getMCAsmInfo();
+  MDT = &getAnalysis<MachineDominatorTreeWrapperPass>().getDomTree();
 
   releaseMemory();