Execute virtreg kills immediately instead of after processing all uses.

This is safe to do because the physreg has been marked UsedInInstr and the kill flag will be set on the last operand using the virtreg if there are more then one.

llvm-svn: 103933

1 files changed, 16 insertions, 19 deletions

diff --git a/llvm/lib/CodeGen/RegAllocFast.cpp b/llvm/lib/CodeGen/RegAllocFast.cpp
index a6461de55ae..ab9aa99c0bf 100644
--- a/llvm/lib/CodeGen/RegAllocFast.cpp
+++ b/llvm/lib/CodeGen/RegAllocFast.cpp
@@ -563,6 +563,7 @@ unsigned RAFast::reloadVirtReg(MachineInstr *MI, unsigned OpNum,
   bool New;
   tie(LRI, New) = LiveVirtRegs.insert(std::make_pair(VirtReg, LiveReg()));
   LiveReg &LR = LRI->second;
+  MachineOperand &MO = MI->getOperand(OpNum);
   if (New) {
     allocVirtReg(MI, *LRI, Hint);
     const TargetRegisterClass *RC = MRI->getRegClass(VirtReg);
@@ -572,7 +573,6 @@ unsigned RAFast::reloadVirtReg(MachineInstr *MI, unsigned OpNum,
     TII->loadRegFromStackSlot(*MBB, MI, LR.PhysReg, FrameIndex, RC, TRI);
     ++NumLoads;
   } else if (LR.Dirty) {
-    MachineOperand &MO = MI->getOperand(OpNum);
     if (isLastUseOfLocalReg(MO)) {
       DEBUG(dbgs() << "Killing last use: " << MO << "\n");
       MO.setIsKill();
@@ -580,6 +580,13 @@ unsigned RAFast::reloadVirtReg(MachineInstr *MI, unsigned OpNum,
       DEBUG(dbgs() << "Clearing dubious kill: " << MO << "\n");
       MO.setIsKill(false);
     }
+  } else if (MO.isKill()) {
+    // We must remove kill flags from uses of reloaded registers because the
+    // register would be killed immediately, and there might be a second use:
+    //   %foo = OR %x<kill>, %x
+    // This would cause a second reload of %x into a different register.
+    DEBUG(dbgs() << "Clearing clean kill: " << MO << "\n");
+    MO.setIsKill(false);
   }
   assert(LR.PhysReg && "Register not assigned");
   LR.LastUse = MI;
@@ -630,7 +637,7 @@ void RAFast::AllocateBasicBlock() {
          E = MBB->livein_end(); I != E; ++I)
     definePhysReg(MII, *I, regReserved);
 
-  SmallVector<unsigned, 8> VirtKills, PhysDefs;
+  SmallVector<unsigned, 8> PhysECs;
   SmallVector<MachineInstr*, 32> Coalesced;
 
   // Otherwise, sequentially allocate each instruction in the MBB.
@@ -694,7 +701,7 @@ void RAFast::AllocateBasicBlock() {
 
     // Track registers used by instruction.
     UsedInInstr.reset();
-    PhysDefs.clear();
+    PhysECs.clear();
 
     // First scan.
     // Mark physreg uses and early clobbers as used.
@@ -714,7 +721,7 @@ void RAFast::AllocateBasicBlock() {
         usePhysReg(MO);
       } else if (MO.isEarlyClobber()) {
         definePhysReg(MI, Reg, MO.isDead() ? regFree : regReserved);
-        PhysDefs.push_back(Reg);
+        PhysECs.push_back(Reg);
       }
     }
 
@@ -730,25 +737,20 @@ void RAFast::AllocateBasicBlock() {
         unsigned PhysReg = reloadVirtReg(MI, i, Reg, CopyDst);
         CopySrc = (CopySrc == Reg || CopySrc == PhysReg) ? PhysReg : 0;
         if (setPhysReg(MO, PhysReg))
-          VirtKills.push_back(Reg);
+          killVirtReg(Reg);
       } else if (MO.isEarlyClobber()) {
         unsigned PhysReg = defineVirtReg(MI, i, Reg, 0);
         setPhysReg(MO, PhysReg);
-        PhysDefs.push_back(PhysReg);
+        PhysECs.push_back(PhysReg);
       }
     }
 
-    // Process virtreg kills
-    for (unsigned i = 0, e = VirtKills.size(); i != e; ++i)
-      killVirtReg(VirtKills[i]);
-    VirtKills.clear();
-
     MRI->addPhysRegsUsed(UsedInInstr);
 
     // Track registers defined by instruction - early clobbers at this point.
     UsedInInstr.reset();
-    for (unsigned i = 0, e = PhysDefs.size(); i != e; ++i) {
-      unsigned PhysReg = PhysDefs[i];
+    for (unsigned i = 0, e = PhysECs.size(); i != e; ++i) {
+      unsigned PhysReg = PhysECs[i];
       UsedInInstr.set(PhysReg);
       for (const unsigned *AS = TRI->getAliasSet(PhysReg);
             unsigned Alias = *AS; ++AS)
@@ -781,17 +783,12 @@ void RAFast::AllocateBasicBlock() {
       }
       unsigned PhysReg = defineVirtReg(MI, i, Reg, CopySrc);
       if (setPhysReg(MO, PhysReg)) {
-        VirtKills.push_back(Reg);
+        killVirtReg(Reg);
         CopyDst = 0; // cancel coalescing;
       } else
         CopyDst = (CopyDst == Reg || CopyDst == PhysReg) ? PhysReg : 0;
     }
 
-    // Process virtreg deads.
-    for (unsigned i = 0, e = VirtKills.size(); i != e; ++i)
-      killVirtReg(VirtKills[i]);
-    VirtKills.clear();
-
     MRI->addPhysRegsUsed(UsedInInstr);
 
     if (CopyDst && CopyDst == CopySrc && CopyDstSub == CopySrcSub) {