[llvm-commits] [llvm] r85026 - /llvm/trunk/lib/CodeGen/RegisterScavenging.cpp

[Jim Grosbach]

Author: grosbach
Date: Sat Oct 24 19:45:07 2009
New Revision: 85026

URL: http://llvm.org/viewvc/llvm-project?rev=85026&view=rev
Log:
When the scavenger is looking for a good candidate location to restore from a
spill, it should avoid doing so inside the live range of a virtual register.

Modified:
    llvm/trunk/lib/CodeGen/RegisterScavenging.cpp

Modified: llvm/trunk/lib/CodeGen/RegisterScavenging.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/RegisterScavenging.cpp?rev=85026&r1=85025&r2=85026&view=diff

==============================================================================
--- llvm/trunk/lib/CodeGen/RegisterScavenging.cpp (original)
+++ llvm/trunk/lib/CodeGen/RegisterScavenging.cpp Sat Oct 24 19:45:07 2009
@@ -227,7 +227,7 @@
 ///
 /// No more than InstrLimit instructions are inspected.
 ///
-unsigned RegScavenger::findSurvivorReg(MachineBasicBlock::iterator MI,
+unsigned RegScavenger::findSurvivorReg(MachineBasicBlock::iterator StartMI,
                                        BitVector &Candidates,
                                        unsigned InstrLimit,
                                        MachineBasicBlock::iterator &UseMI) {
@@ -235,19 +235,37 @@
   assert(Survivor > 0 && "No candidates for scavenging");
 
   MachineBasicBlock::iterator ME = MBB->getFirstTerminator();
-  assert(MI != ME && "MI already at terminator");
+  assert(StartMI != ME && "MI already at terminator");
+  MachineBasicBlock::iterator RestorePointMI = StartMI;
+  MachineBasicBlock::iterator MI = StartMI;
 
+  bool inVirtLiveRange = false;
   for (++MI; InstrLimit > 0 && MI != ME; ++MI, --InstrLimit) {
+    bool isVirtKillInsn = false;
+    bool isVirtDefInsn = false;
     // Remove any candidates touched by instruction.
     for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
       const MachineOperand &MO = MI->getOperand(i);
-      if (!MO.isReg() || MO.isUndef() || !MO.getReg() ||
-          TargetRegisterInfo::isVirtualRegister(MO.getReg()))
+      if (!MO.isReg() || MO.isUndef() || !MO.getReg())
         continue;
+      if (TargetRegisterInfo::isVirtualRegister(MO.getReg())) {
+        if (MO.isDef())
+          isVirtDefInsn = true;
+        else if (MO.isKill())
+          isVirtKillInsn = true;
+        continue;
+      }
       Candidates.reset(MO.getReg());
       for (const unsigned *R = TRI->getAliasSet(MO.getReg()); *R; R++)
         Candidates.reset(*R);
     }
+    // If we're not in a virtual reg's live range, this is a valid
+    // restore point.
+    if (!inVirtLiveRange) RestorePointMI = MI;
+
+    // Update whether we're in the live range of a virtual register
+    if (isVirtKillInsn) inVirtLiveRange = false;
+    if (isVirtDefInsn) inVirtLiveRange = true;
 
     // Was our survivor untouched by this instruction?
     if (Candidates.test(Survivor))
@@ -259,9 +277,13 @@
 
     Survivor = Candidates.find_first();
   }
+  // If we ran off the end, that's where we want to restore.
+  if (MI == ME) RestorePointMI = ME;
+  assert (RestorePointMI != StartMI &&
+          "No available scavenger restore location!");
 
   // We ran out of candidates, so stop the search.
-  UseMI = MI;
+  UseMI = RestorePointMI;
   return Survivor;
 }