[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, 1 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/MachineBlockPlacement.cpp b/llvm/lib/CodeGen/MachineBlockPlacement.cpp
index 6179e09..9010c3c 100644
--- a/llvm/lib/CodeGen/MachineBlockPlacement.cpp
+++ b/llvm/lib/CodeGen/MachineBlockPlacement.cpp
@@ -3649,6 +3649,7 @@ void MachineBlockPlacement::assignBlockOrder(
     const std::vector<const MachineBasicBlock *> &NewBlockOrder) {
   assert(F->size() == NewBlockOrder.size() && "Incorrect size of block order");
   F->RenumberBlocks();
+  MPDT->updateBlockNumbers();
 
   bool HasChanges = false;
   for (size_t I = 0; I < NewBlockOrder.size(); I++) {