X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FCodeGen%2FMachineCSE.cpp;h=ae26967b235e8fab483674c6a0d7604ea5fea42e;hb=25529b337f75a4b9b174592e2c95136e781bd824;hp=9c3bcc444c44aa821fd1637b32b0fa7f51f0e94f;hpb=5fa58a5b232be0b8261041a651ed1be3ae8d3848;p=oota-llvm.git

diff --git a/lib/CodeGen/MachineCSE.cpp b/lib/CodeGen/MachineCSE.cpp
index 9c3bcc444c4..ae26967b235 100644
--- a/lib/CodeGen/MachineCSE.cpp
+++ b/lib/CodeGen/MachineCSE.cpp
@@ -13,7 +13,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-#define DEBUG_TYPE "machine-cse"
 #include "llvm/CodeGen/Passes.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/ScopedHashTable.h"
@@ -26,8 +25,11 @@
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/RecyclingAllocator.h"
 #include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/Target/TargetSubtargetInfo.h"
 using namespace llvm;
 
+#define DEBUG_TYPE "machine-cse"
+
 STATISTIC(NumCoalesces, "Number of copies coalesced");
 STATISTIC(NumCSEs,      "Number of common subexpression eliminated");
 STATISTIC(NumPhysCSEs,
@@ -77,7 +79,8 @@ namespace {
     SmallVector<MachineInstr*, 64> Exps;
     unsigned CurrVN;
 
-    bool PerformTrivialCoalescing(MachineInstr *MI, MachineBasicBlock *MBB);
+    bool PerformTrivialCopyPropagation(MachineInstr *MI,
+                                       MachineBasicBlock *MBB);
     bool isPhysDefTriviallyDead(unsigned Reg,
                                 MachineBasicBlock::const_iterator I,
                                 MachineBasicBlock::const_iterator E) const;
@@ -111,8 +114,12 @@ INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
 INITIALIZE_PASS_END(MachineCSE, "machine-cse",
                 "Machine Common Subexpression Elimination", false, false)
 
-bool MachineCSE::PerformTrivialCoalescing(MachineInstr *MI,
-                                          MachineBasicBlock *MBB) {
+/// The source register of a COPY machine instruction can be propagated to all
+/// its users, and this propagation could increase the probability of finding
+/// common subexpressions. If the COPY has only one user, the COPY itself can
+/// be removed.
+bool MachineCSE::PerformTrivialCopyPropagation(MachineInstr *MI,
+                                               MachineBasicBlock *MBB) {
   bool Changed = false;
   for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
     MachineOperand &MO = MI->getOperand(i);
@@ -121,10 +128,7 @@ bool MachineCSE::PerformTrivialCoalescing(MachineInstr *MI,
     unsigned Reg = MO.getReg();
     if (!TargetRegisterInfo::isVirtualRegister(Reg))
       continue;
-    if (!MRI->hasOneNonDBGUse(Reg))
-      // Only coalesce single use copies. This ensure the copy will be
-      // deleted.
-      continue;
+    bool OnlyOneUse = MRI->hasOneNonDBGUse(Reg);
     MachineInstr *DefMI = MRI->getVRegDef(Reg);
     if (!DefMI->isCopy())
       continue;
@@ -152,10 +156,14 @@ bool MachineCSE::PerformTrivialCoalescing(MachineInstr *MI,
       continue;
     DEBUG(dbgs() << "Coalescing: " << *DefMI);
     DEBUG(dbgs() << "***     to: " << *MI);
+    // Propagate SrcReg of copies to MI.
     MO.setReg(SrcReg);
     MRI->clearKillFlags(SrcReg);
-    DefMI->eraseFromParent();
-    ++NumCoalesces;
+    // Coalesce single use copies.
+    if (OnlyOneUse) {
+      DefMI->eraseFromParent();
+      ++NumCoalesces;
+    }
     Changed = true;
   }
 
@@ -379,7 +387,7 @@ bool MachineCSE::isProfitableToCSE(unsigned CSReg, unsigned Reg,
   // Heuristics #1: Don't CSE "cheap" computation if the def is not local or in
   // an immediate predecessor. We don't want to increase register pressure and
   // end up causing other computation to be spilled.
-  if (MI->isAsCheapAsAMove()) {
+  if (TII->isAsCheapAsAMove(MI)) {
     MachineBasicBlock *CSBB = CSMI->getParent();
     MachineBasicBlock *BB = MI->getParent();
     if (CSBB != BB && !CSBB->isSuccessor(BB))
@@ -452,13 +460,15 @@ bool MachineCSE::ProcessBlock(MachineBasicBlock *MBB) {
 
     bool FoundCSE = VNT.count(MI);
     if (!FoundCSE) {
-      // Look for trivial copy coalescing opportunities.
-      if (PerformTrivialCoalescing(MI, MBB)) {
+      // Using trivial copy propagation to find more CSE opportunities.
+      if (PerformTrivialCopyPropagation(MI, MBB)) {
         Changed = true;
 
         // After coalescing MI itself may become a copy.
         if (MI->isCopyLike())
           continue;
+
+        // Try again to see if CSE is possible.
         FoundCSE = VNT.count(MI);
       }
     }
@@ -662,8 +672,8 @@ bool MachineCSE::runOnMachineFunction(MachineFunction &MF) {
   if (skipOptnoneFunction(*MF.getFunction()))
     return false;
 
-  TII = MF.getTarget().getInstrInfo();
-  TRI = MF.getTarget().getRegisterInfo();
+  TII = MF.getSubtarget().getInstrInfo();
+  TRI = MF.getSubtarget().getRegisterInfo();
   MRI = &MF.getRegInfo();
   AA = &getAnalysis<AliasAnalysis>();
   DT = &getAnalysis<MachineDominatorTree>();