Create a more targeted fix for not sinking instructions into a range where it

will conflict with another live range. The place which creates this scenerio is
the code in X86 that lowers a select instruction by splitting the MBBs. This
eliminates the need to check from the bottom up in an MBB for live pregs.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@106066 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 10 insertions, 50 deletions

diff --git a/lib/CodeGen/MachineSink.cpp b/lib/CodeGen/MachineSink.cpp
index 4a9ea72b05..61334fc179 100644
--- a/lib/CodeGen/MachineSink.cpp
+++ b/lib/CodeGen/MachineSink.cpp
@@ -25,7 +25,6 @@
 #include "llvm/Target/TargetRegisterInfo.h"
 #include "llvm/Target/TargetInstrInfo.h"
 #include "llvm/Target/TargetMachine.h"
-#include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
@@ -62,7 +61,6 @@ namespace {
     bool ProcessBlock(MachineBasicBlock &MBB);
     bool SinkInstruction(MachineInstr *MI, bool &SawStore);
     bool AllUsesDominatedByBlock(unsigned Reg, MachineBasicBlock *MBB) const;
-    bool LiveOutOfBasicBlock(const MachineInstr *MI, unsigned Reg) const;
   };
 } // end anonymous namespace
 
@@ -168,44 +166,6 @@ bool MachineSinking::ProcessBlock(MachineBasicBlock &MBB) {
   return MadeChange;
 }
 
-/// LiveOutOfBasicBlock - Determine if the physical register, defined and dead
-/// in MI, is live on exit from the basic block.
-bool MachineSinking::LiveOutOfBasicBlock(const MachineInstr *MI,
-                                         unsigned Reg) const {
-  assert(TargetRegisterInfo::isPhysicalRegister(Reg) &&
-         "Only want to determine if a physical register is live out of a BB!");
-
-  const MachineBasicBlock *MBB = MI->getParent();
-  SmallSet<unsigned, 8> KilledRegs;
-  MachineBasicBlock::const_iterator I = MBB->end();
-  MachineBasicBlock::const_iterator E = MBB->begin();
-  assert(I != E && "How can there be an empty block at this point?!");
-
-  // Loop through the instructions bottom-up. If we see a kill of the preg
-  // first, then it's not live out of the BB. If we see a use or def first, then
-  // we assume that it is live out of the BB.
-  do {
-    const MachineInstr &CurMI = *--I;
-
-    for (unsigned i = 0, e = CurMI.getNumOperands(); i != e; ++i) {
-      const MachineOperand &MO = CurMI.getOperand(i);
-      if (!MO.isReg()) continue;  // Ignore non-register operands.
-
-      unsigned MOReg = MO.getReg();
-      if (MOReg == 0) continue;
-
-      if (MOReg == Reg) {
-        if (MO.isKill())
-          return false;
-        if (MO.isUse() || MO.isDef())
-          return true;
-      }
-    }
-  } while (I != E);
-
-  return false;
-}
-
 /// SinkInstruction - Determine whether it is safe to sink the specified machine
 /// instruction out of its current block into a successor.
 bool MachineSinking::SinkInstruction(MachineInstr *MI, bool &SawStore) {
@@ -228,7 +188,6 @@ bool MachineSinking::SinkInstruction(MachineInstr *MI, bool &SawStore) {
   // SuccToSinkTo - This is the successor to sink this instruction to, once we
   // decide.
   MachineBasicBlock *SuccToSinkTo = 0;
-  SmallVector<unsigned, 4> PhysRegs;
 
   for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
     const MachineOperand &MO = MI->getOperand(i);
@@ -257,12 +216,9 @@ bool MachineSinking::SinkInstruction(MachineInstr *MI, bool &SawStore) {
           if (AllocatableSet.test(AliasReg))
             return false;
         }
-      } else {
-        if (!MO.isDead())
-          // A def that isn't dead. We can't move it.
-          return false;
-        else
-          PhysRegs.push_back(Reg);
+      } else if (!MO.isDead()) {
+        // A def that isn't dead. We can't move it.
+        return false;
       }
     } else {
       // Virtual register uses are always safe to sink.
@@ -329,10 +285,14 @@ bool MachineSinking::SinkInstruction(MachineInstr *MI, bool &SawStore) {
   // If the instruction to move defines a dead physical register which is live
   // when leaving the basic block, don't move it because it could turn into a
   // "zombie" define of that preg. E.g., EFLAGS. (<rdar://problem/8030636>)
-  for (SmallVectorImpl<unsigned>::const_iterator
-         I = PhysRegs.begin(), E = PhysRegs.end(); I != E; ++I)
-    if (LiveOutOfBasicBlock(MI, *I))
+  for (unsigned I = 0, E = MI->getNumOperands(); I != E; ++I) {
+    const MachineOperand &MO = MI->getOperand(I);
+    if (!MO.isReg()) continue;
+    unsigned Reg = MO.getReg();
+    if (Reg == 0 || !TargetRegisterInfo::isPhysicalRegister(Reg)) continue;
+    if (SuccToSinkTo->isLiveIn(Reg))
       return false;
+  }
 
   DEBUG(dbgs() << "Sink instr " << *MI << "\tinto block " << *SuccToSinkTo);