[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/MachineFunction.cpp b/llvm/lib/CodeGen/MachineFunction.cpp
index 40bde20..ab45663 100644
--- a/llvm/lib/CodeGen/MachineFunction.cpp
+++ b/llvm/lib/CodeGen/MachineFunction.cpp
@@ -375,6 +375,7 @@ void MachineFunction::RenumberBlocks(MachineBasicBlock *MBB) {
   // numbering, shrink MBBNumbering now.
   assert(BlockNo <= MBBNumbering.size() && "Mismatch!");
   MBBNumbering.resize(BlockNo);
+  MBBNumberingEpoch++;
 }
 
 /// This method iterates over the basic blocks and assigns their IsBeginSection