From 58156715b4038928c87615fcbb2c223e3c33a57f Mon Sep 17 00:00:00 2001
From: Sjoerd Meijer <sjoerd.meijer@arm.com>
Date: Mon, 15 Aug 2016 08:22:42 +0000
Subject: 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
---
 llvm/lib/CodeGen/MachineLoopInfo.cpp | 45 ++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

(limited to 'llvm/lib/CodeGen/MachineLoopInfo.cpp')

diff --git a/llvm/lib/CodeGen/MachineLoopInfo.cpp b/llvm/lib/CodeGen/MachineLoopInfo.cpp
index 376f78f..fdeaf7b 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());
-- 
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