From bc2453dd3de1b2e34c0830fd69b0255a25ea485e Mon Sep 17 00:00:00 2001
From: Evan Cheng <evan.cheng@apple.com>
Date: Wed, 30 May 2012 00:42:39 +0000
Subject: Teach taildup to update livein set. rdar://11538365

llvm-svn: 157663
---
 llvm/lib/CodeGen/TailDuplication.cpp | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

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

diff --git a/llvm/lib/CodeGen/TailDuplication.cpp b/llvm/lib/CodeGen/TailDuplication.cpp
index 3e203850f90..d077b091937 100644
--- a/llvm/lib/CodeGen/TailDuplication.cpp
+++ b/llvm/lib/CodeGen/TailDuplication.cpp
@@ -20,7 +20,9 @@
 #include "llvm/CodeGen/MachineInstrBuilder.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/CodeGen/MachineSSAUpdater.h"
+#include "llvm/CodeGen/RegisterScavenging.h"
 #include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/Target/TargetRegisterInfo.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/ErrorHandling.h"
@@ -57,8 +59,10 @@ namespace {
   /// TailDuplicatePass - Perform tail duplication.
   class TailDuplicatePass : public MachineFunctionPass {
     const TargetInstrInfo *TII;
+    const TargetRegisterInfo *TRI;
     MachineModuleInfo *MMI;
     MachineRegisterInfo *MRI;
+    RegScavenger *RS;
     bool PreRegAlloc;
 
     // SSAUpdateVRs - A list of virtual registers for which to update SSA form.
@@ -124,9 +128,13 @@ INITIALIZE_PASS(TailDuplicatePass, "tailduplication", "Tail Duplication",
 
 bool TailDuplicatePass::runOnMachineFunction(MachineFunction &MF) {
   TII = MF.getTarget().getInstrInfo();
+  TRI = MF.getTarget().getRegisterInfo();
   MRI = &MF.getRegInfo();
   MMI = getAnalysisIfAvailable<MachineModuleInfo>();
   PreRegAlloc = MRI->isSSA();
+  RS = NULL;
+  if (MRI->tracksLiveness() && TRI->trackLivenessAfterRegAlloc(MF))
+    RS = new RegScavenger();
 
   bool MadeChange = false;
   while (TailDuplicateBlocks(MF))
@@ -777,6 +785,23 @@ TailDuplicatePass::TailDuplicate(MachineBasicBlock *TailBB,
     // Remove PredBB's unconditional branch.
     TII->RemoveBranch(*PredBB);
 
+    if (RS && !TailBB->livein_empty()) {
+      // Update PredBB livein.
+      RS->enterBasicBlock(PredBB);
+      if (!PredBB->empty())
+        RS->forward(prior(PredBB->end()));
+      BitVector RegsLiveAtExit(TRI->getNumRegs());
+      RS->getRegsUsed(RegsLiveAtExit, false);
+      for (MachineBasicBlock::livein_iterator I = TailBB->livein_begin(),
+             E = TailBB->livein_end(); I != E; ++I) {
+        if (!RegsLiveAtExit[*I])
+          // If a register is previously livein to the tail but it's not live
+          // at the end of predecessor BB, then it should be added to its
+          // livein list.
+          PredBB->addLiveIn(*I);
+      }
+    }
+
     // Clone the contents of TailBB into PredBB.
     DenseMap<unsigned, unsigned> LocalVRMap;
     SmallVector<std::pair<unsigned,unsigned>, 4> CopyInfos;
-- 
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