X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FCodeGen%2FMachineCopyPropagation.cpp;h=e41d3eee216a7c54901cf627bf1265213733f390;hb=34fa5640b805e6bc7a8259e181eed64051c09b4e;hp=4f48e2cd9720a96d3ada07f5fec611ba3174e22f;hpb=62c320a755ac27ac2b7f64e927892249e0f486e0;p=oota-llvm.git

diff --git a/lib/CodeGen/MachineCopyPropagation.cpp b/lib/CodeGen/MachineCopyPropagation.cpp
index 4f48e2cd972..e41d3eee216 100644
--- a/lib/CodeGen/MachineCopyPropagation.cpp
+++ b/lib/CodeGen/MachineCopyPropagation.cpp
@@ -127,13 +127,10 @@ static bool isNopCopy(MachineInstr *CopyMI, unsigned Def, unsigned Src,
 }
 
 // Remove MI from the function because it has been determined it is dead.
-// Turn it into a noop KILL instruction if it has super-register liveness
-// adjustments.
+// Turn it into a noop KILL instruction as opposed to removing it to
+// maintain imp-use/imp-def chains.
 void MachineCopyPropagation::removeCopy(MachineInstr *MI) {
-  if (MI->getNumOperands() == 2)
-    MI->eraseFromParent();
-  else
-    MI->setDesc(TII->get(TargetOpcode::KILL));
+  MI->setDesc(TII->get(TargetOpcode::KILL));
 }
 
 bool MachineCopyPropagation::CopyPropagateBlock(MachineBasicBlock &MBB) {
@@ -142,6 +139,8 @@ bool MachineCopyPropagation::CopyPropagateBlock(MachineBasicBlock &MBB) {
   DenseMap<unsigned, MachineInstr*> CopyMap;         // Def -> copies map
   SourceMap SrcMap; // Src -> Def map
 
+  DEBUG(dbgs() << "MCP: CopyPropagateBlock " << MBB.getName() << "\n");
+
   bool Changed = false;
   for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end(); I != E; ) {
     MachineInstr *MI = &*I;
@@ -176,6 +175,8 @@ bool MachineCopyPropagation::CopyPropagateBlock(MachineBasicBlock &MBB) {
           // CALL
           // %RAX<def> = COPY %RSP
 
+          DEBUG(dbgs() << "MCP: copy is a NOP, removing: "; MI->dump());
+
           // Clear any kills of Def between CopyMI and MI. This extends the
           // live range.
           for (MachineBasicBlock::iterator I = CopyMI, E = MI; I != E; ++I)
@@ -191,10 +192,14 @@ bool MachineCopyPropagation::CopyPropagateBlock(MachineBasicBlock &MBB) {
       // If Src is defined by a previous copy, it cannot be eliminated.
       for (MCRegAliasIterator AI(Src, TRI, true); AI.isValid(); ++AI) {
         CI = CopyMap.find(*AI);
-        if (CI != CopyMap.end())
+        if (CI != CopyMap.end()) {
+          DEBUG(dbgs() << "MCP: Copy is no longer dead: "; CI->second->dump());
           MaybeDeadCopies.remove(CI->second);
+        }
       }
 
+      DEBUG(dbgs() << "MCP: Copy is a deletion candidate: "; MI->dump());
+
       // Copy is now a candidate for deletion.
       MaybeDeadCopies.insert(MI);
 
@@ -255,8 +260,10 @@ bool MachineCopyPropagation::CopyPropagateBlock(MachineBasicBlock &MBB) {
       // for elimination.
       for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI) {
         DenseMap<unsigned, MachineInstr*>::iterator CI = CopyMap.find(*AI);
-        if (CI != CopyMap.end())
+        if (CI != CopyMap.end()) {
+          DEBUG(dbgs() << "MCP: Copy is used - not dead: "; CI->second->dump());
           MaybeDeadCopies.remove(CI->second);
+        }
       }
     }
 
@@ -273,6 +280,8 @@ bool MachineCopyPropagation::CopyPropagateBlock(MachineBasicBlock &MBB) {
         unsigned Reg = (*DI)->getOperand(0).getReg();
         if (MRI->isReserved(Reg) || !MaskMO.clobbersPhysReg(Reg))
           continue;
+        DEBUG(dbgs() << "MCP: Removing copy due to regmask clobbering: ";
+              (*DI)->dump());
         removeCopy(*DI);
         Changed = true;
         ++NumDeletes;