Identity copies should not contribute to spill weight.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@84978 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 28 insertions, 4 deletions

diff --git a/include/llvm/Target/TargetInstrInfo.h b/include/llvm/Target/TargetInstrInfo.h
index 919bef1e7f..d64df445b0 100644
--- a/include/llvm/Target/TargetInstrInfo.h
+++ b/include/llvm/Target/TargetInstrInfo.h
@@ -133,13 +133,34 @@ private:
                                                 AliasAnalysis *AA) const;
 
 public:
-  /// Return true if the instruction is a register to register move and return
-  /// the source and dest operands and their sub-register indices by reference.
+  /// isMoveInstr - Return true if the instruction is a register to register
+  /// move and return the source and dest operands and their sub-register
+  /// indices by reference.
   virtual bool isMoveInstr(const MachineInstr& MI,
                            unsigned& SrcReg, unsigned& DstReg,
                            unsigned& SrcSubIdx, unsigned& DstSubIdx) const {
     return false;
   }
+
+  /// isIdentityCopy - Return true if the instruction is a copy (or
+  /// extract_subreg, insert_subreg, subreg_to_reg) where the source and
+  /// destination registers are the same.
+  bool isIdentityCopy(const MachineInstr &MI) const {
+    unsigned SrcReg, DstReg, SrcSubIdx, DstSubIdx;
+    if (isMoveInstr(MI, SrcReg, DstReg, SrcSubIdx, DstSubIdx) &&
+        SrcReg == DstReg)
+      return true;
+
+    if (MI.getOpcode() == TargetInstrInfo::EXTRACT_SUBREG &&
+        MI.getOperand(0).getReg() == MI.getOperand(1).getReg())
+    return true;
+
+    if ((MI.getOpcode() == TargetInstrInfo::INSERT_SUBREG ||
+         MI.getOpcode() == TargetInstrInfo::SUBREG_TO_REG) &&
+        MI.getOperand(0).getReg() == MI.getOperand(2).getReg())
+      return true;
+    return false;
+  }
   
   /// isLoadFromStackSlot - If the specified machine instruction is a direct
   /// load from a stack slot, return the virtual or physical register number of
diff --git a/lib/CodeGen/SimpleRegisterCoalescing.cpp b/lib/CodeGen/SimpleRegisterCoalescing.cpp
index 9c283b0f02..827d6dc5f4 100644
--- a/lib/CodeGen/SimpleRegisterCoalescing.cpp
+++ b/lib/CodeGen/SimpleRegisterCoalescing.cpp
@@ -2556,6 +2556,7 @@ static bool isZeroLengthInterval(LiveInterval *li, LiveIntervals *li_) {
   return true;
 }
 
+
 void SimpleRegisterCoalescing::CalculateSpillWeights() {
   SmallSet<unsigned, 4> Processed;
   for (MachineFunction::iterator mbbi = mf_->begin(), mbbe = mf_->end();
@@ -2566,9 +2567,11 @@ void SimpleRegisterCoalescing::CalculateSpillWeights() {
     unsigned loopDepth = loop ? loop->getLoopDepth() : 0;
     bool isExit = loop ? loop->isLoopExit(MBB) : false;
 
-    for (MachineBasicBlock::iterator mii = MBB->begin(), mie = MBB->end();
+    for (MachineBasicBlock::const_iterator mii = MBB->begin(), mie = MBB->end();
          mii != mie; ++mii) {
-      MachineInstr *MI = mii;
+      const MachineInstr *MI = mii;
+      if (tii_->isIdentityCopy(*MI))
+        continue;
 
       for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
         const MachineOperand &mopi = MI->getOperand(i);