From: Evan Cheng <evan.cheng@apple.com>
Date: Tue, 17 Aug 2010 17:43:50 +0000 (+0000)
Subject: Move the decision logic whether it's a good idea to split a critical edge to clients... 
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=e008384508342a2dec110eafaa87d93614976990;p=oota-llvm.git

Move the decision logic whether it's a good idea to split a critical edge to clients. Also fixed an erroneous check. An edge is only a back edge when the from and to blocks are in the same loop.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@111256 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/CodeGen/MachineBasicBlock.cpp b/lib/CodeGen/MachineBasicBlock.cpp
index f506f12050a..d351db59e69 100644
--- a/lib/CodeGen/MachineBasicBlock.cpp
+++ b/lib/CodeGen/MachineBasicBlock.cpp
@@ -439,14 +439,6 @@ MachineBasicBlock::SplitCriticalEdge(MachineBasicBlock *Succ, Pass *P) {
   if (TII->AnalyzeBranch(*this, TBB, FBB, Cond))
     return NULL;
 
-  // Avoid splitting backedges of loops. It would introduce small out-of-line
-  // blocks into the loop which is very bad for code placement.
-  if (this == Succ)
-    return NULL;
-  MachineLoopInfo *MLI = P->getAnalysisIfAvailable<MachineLoopInfo>();
-  if (MLI->isLoopHeader(Succ))
-    return NULL;
-
   MachineBasicBlock *NMBB = MF->CreateMachineBasicBlock();
   MF->insert(llvm::next(MachineFunction::iterator(this)), NMBB);
   DEBUG(dbgs() << "Splitting critical edge:"
@@ -479,7 +471,7 @@ MachineBasicBlock::SplitCriticalEdge(MachineBasicBlock *Succ, Pass *P) {
         P->getAnalysisIfAvailable<MachineDominatorTree>())
     MDT->addNewBlock(NMBB, this);
 
-  if (MLI)
+  if (MachineLoopInfo *MLI = P->getAnalysisIfAvailable<MachineLoopInfo>())
     if (MachineLoop *TIL = MLI->getLoopFor(this)) {
       // If one or the other blocks were not in a loop, the new block is not
       // either, and thus LI doesn't need to be updated.
diff --git a/lib/CodeGen/PHIElimination.cpp b/lib/CodeGen/PHIElimination.cpp
index 105f20b4489..11566c2d866 100644
--- a/lib/CodeGen/PHIElimination.cpp
+++ b/lib/CodeGen/PHIElimination.cpp
@@ -53,6 +53,7 @@ void llvm::PHIElimination::getAnalysisUsage(AnalysisUsage &AU) const {
 
 bool llvm::PHIElimination::runOnMachineFunction(MachineFunction &MF) {
   MRI = &MF.getRegInfo();
+  MLI = getAnalysisIfAvailable<MachineLoopInfo>();
 
   bool Changed = false;
 
@@ -392,8 +393,14 @@ bool llvm::PHIElimination::SplitPHIEdges(MachineFunction &MF,
       // We break edges when registers are live out from the predecessor block
       // (not considering PHI nodes). If the register is live in to this block
       // anyway, we would gain nothing from splitting.
-      if (!LV.isLiveIn(Reg, MBB) && LV.isLiveOut(Reg, *PreMBB))
-        Changed |= PreMBB->SplitCriticalEdge(&MBB, this) != 0;
+      // Avoid splitting backedges of loops. It would introduce small
+      // out-of-line blocks into the loop which is very bad for code placement.
+      if (PreMBB != &MBB &&
+          !LV.isLiveIn(Reg, MBB) && LV.isLiveOut(Reg, *PreMBB)) {
+        if (!(MLI->getLoopFor(PreMBB) == MLI->getLoopFor(&MBB) &&
+              MLI->isLoopHeader(&MBB)))
+          Changed |= PreMBB->SplitCriticalEdge(&MBB, this) != 0;
+      }
     }
   }
   return true;
diff --git a/lib/CodeGen/PHIElimination.h b/lib/CodeGen/PHIElimination.h
index f183de6149c..b054732dace 100644
--- a/lib/CodeGen/PHIElimination.h
+++ b/lib/CodeGen/PHIElimination.h
@@ -13,15 +13,18 @@
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/CodeGen/MachineBasicBlock.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
-#include "llvm/CodeGen/MachineRegisterInfo.h"
 
 namespace llvm {
   class LiveVariables;
+  class MachineRegisterInfo;
+  class MachineLoopInfo;
   
   /// Lower PHI instructions to copies.  
   class PHIElimination : public MachineFunctionPass {
-    MachineRegisterInfo  *MRI; // Machine register information
+    MachineRegisterInfo *MRI; // Machine register information
+    MachineLoopInfo     *MLI;
 
   public:
     static char ID; // Pass identification, replacement for typeid