[DomTreeUpdater] Move critical edge splitting code to updater (#115111)

Support critical edge splitting in dominator tree updater. Continue the
work in #100856.

Compile time check:
https://llvm-compile-time-tracker.com/compare.php?from=87c35d782795b54911b3e3a91a5b738d4d870e55&to=42b3e5623a9ab4c3648564dc0926b36f3b438a3a&stat=instructions%3Au

1 files changed, 18 insertions, 9 deletions

diff --git a/llvm/lib/CodeGen/PHIElimination.cpp b/llvm/lib/CodeGen/PHIElimination.cpp
index e5f4077..b71e5b8 100644
--- a/llvm/lib/CodeGen/PHIElimination.cpp
+++ b/llvm/lib/CodeGen/PHIElimination.cpp
@@ -22,6 +22,7 @@
 #include "llvm/CodeGen/LiveIntervals.h"
 #include "llvm/CodeGen/LiveVariables.h"
 #include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/CodeGen/MachineDomTreeUpdater.h"
 #include "llvm/CodeGen/MachineDominators.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
@@ -90,7 +91,8 @@ class PHIEliminationImpl {
   /// Split critical edges where necessary for good coalescer performance.
   bool SplitPHIEdges(MachineFunction &MF, MachineBasicBlock &MBB,
                      MachineLoopInfo *MLI,
-                     std::vector<SparseBitVector<>> *LiveInSets);
+                     std::vector<SparseBitVector<>> *LiveInSets,
+                     MachineDomTreeUpdater &MDTU);
 
   // These functions are temporary abstractions around LiveVariables and
   // LiveIntervals, so they can go away when LiveVariables does.
@@ -203,6 +205,16 @@ void PHIElimination::getAnalysisUsage(AnalysisUsage &AU) const {
 bool PHIEliminationImpl::run(MachineFunction &MF) {
   MRI = &MF.getRegInfo();
 
+  MachineDominatorTree *MDT = nullptr;
+  if (P) {
+    auto *MDTWrapper =
+        P->getAnalysisIfAvailable<MachineDominatorTreeWrapperPass>();
+    MDT = MDTWrapper ? &MDTWrapper->getDomTree() : nullptr;
+  } else {
+    MDT = MFAM->getCachedResult<MachineDominatorTreeAnalysis>(MF);
+  }
+  MachineDomTreeUpdater MDTU(MDT, MachineDomTreeUpdater::UpdateStrategy::Lazy);
+
   bool Changed = false;
 
   // Split critical edges to help the coalescer.
@@ -237,7 +249,8 @@ bool PHIEliminationImpl::run(MachineFunction &MF) {
     }
 
     for (auto &MBB : MF)
-      Changed |= SplitPHIEdges(MF, MBB, MLI, (LV ? &LiveInSets : nullptr));
+      Changed |=
+          SplitPHIEdges(MF, MBB, MLI, (LV ? &LiveInSets : nullptr), MDTU);
   }
 
   // This pass takes the function out of SSA form.
@@ -268,10 +281,6 @@ bool PHIEliminationImpl::run(MachineFunction &MF) {
     MF.deleteMachineInstr(I.first);
   }
 
-  // TODO: we should use the incremental DomTree updater here.
-  if (Changed && MDT)
-    MDT->getBase().recalculate(MF);
-
   LoweredPHIs.clear();
   ImpDefs.clear();
   VRegPHIUseCount.clear();
@@ -752,7 +761,7 @@ void PHIEliminationImpl::analyzePHINodes(const MachineFunction &MF) {
 
 bool PHIEliminationImpl::SplitPHIEdges(
     MachineFunction &MF, MachineBasicBlock &MBB, MachineLoopInfo *MLI,
-    std::vector<SparseBitVector<>> *LiveInSets) {
+    std::vector<SparseBitVector<>> *LiveInSets, MachineDomTreeUpdater &MDTU) {
   if (MBB.empty() || !MBB.front().isPHI() || MBB.isEHPad())
     return false; // Quick exit for basic blocks without PHIs.
 
@@ -819,8 +828,8 @@ bool PHIEliminationImpl::SplitPHIEdges(
       }
       if (!ShouldSplit && !SplitAllCriticalEdges)
         continue;
-      if (!(P ? PreMBB->SplitCriticalEdge(&MBB, *P, LiveInSets)
-              : PreMBB->SplitCriticalEdge(&MBB, *MFAM, LiveInSets))) {
+      if (!(P ? PreMBB->SplitCriticalEdge(&MBB, *P, LiveInSets, &MDTU)
+              : PreMBB->SplitCriticalEdge(&MBB, *MFAM, LiveInSets, &MDTU))) {
         LLVM_DEBUG(dbgs() << "Failed to split critical edge.\n");
         continue;
       }