MachineLoop: add methods findLoopControlBlock and findLoopPreheader

This adds two new utility functions findLoopControlBlock and findLoopPreheader
to MachineLoop and MachineLoopInfo. These functions are refactored and taken
from the Hexagon target as they are target independent; thus this is intendend to
be a non-functional change.

Differential Revision: https://reviews.llvm.org/D22959

llvm-svn: 278661

1 files changed, 45 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/MachineLoopInfo.cpp b/llvm/lib/CodeGen/MachineLoopInfo.cpp
index 376f78fda1c..fdeaf7b7116 100644
--- a/llvm/lib/CodeGen/MachineLoopInfo.cpp
+++ b/llvm/lib/CodeGen/MachineLoopInfo.cpp
@@ -77,6 +77,51 @@ MachineBasicBlock *MachineLoop::getBottomBlock() {
   return BotMBB;
 }
 
+MachineBasicBlock *MachineLoop::findLoopControlBlock() {
+  if (MachineBasicBlock *Latch = getLoopLatch()) {
+    if (isLoopExiting(Latch))
+      return Latch;
+    else
+      return getExitingBlock();
+  }
+  return nullptr;
+}
+
+MachineBasicBlock *
+MachineLoopInfo::findLoopPreheader(MachineLoop *L,
+                                   bool SpeculativePreheader) const {
+  if (MachineBasicBlock *PB = L->getLoopPreheader())
+    return PB;
+
+  if (!SpeculativePreheader)
+    return nullptr;
+
+  MachineBasicBlock *HB = L->getHeader(), *LB = L->getLoopLatch();
+  if (HB->pred_size() != 2 || HB->hasAddressTaken())
+    return nullptr;
+  // Find the predecessor of the header that is not the latch block.
+  MachineBasicBlock *Preheader = nullptr;
+  for (MachineBasicBlock *P : HB->predecessors()) {
+    if (P == LB)
+      continue;
+    // Sanity.
+    if (Preheader)
+      return nullptr;
+    Preheader = P;
+  }
+
+  // Check if the preheader candidate is a successor of any other loop
+  // headers. We want to avoid having two loop setups in the same block.
+  for (MachineBasicBlock *S : Preheader->successors()) {
+    if (S == HB)
+      continue;
+    MachineLoop *T = getLoopFor(S);
+    if (T && T->getHeader() == S)
+      return nullptr;
+  }
+  return Preheader;
+}
+
 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
 LLVM_DUMP_METHOD void MachineLoop::dump() const {
   print(dbgs());