Copy coalescing change to prevent a physical register from being pin to a

long live interval that has low usage density.
1. Change order of coalescing to join physical registers with virtual
   registers first before virtual register intervals become too long.
2. Check size and usage density to determine if it's worthwhile to join.
3. If joining is aborted, assign virtual register live interval allocation
   preference field to the physical register.
4. Register allocator should try to allocate to the preferred register
   first (if available) to create identify moves that can be eliminated.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@36218 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 6 insertions, 2 deletions

diff --git a/include/llvm/CodeGen/LiveIntervalAnalysis.h b/include/llvm/CodeGen/LiveIntervalAnalysis.h
index 641ff6a0b4..a793e151d3 100644
--- a/include/llvm/CodeGen/LiveIntervalAnalysis.h
+++ b/include/llvm/CodeGen/LiveIntervalAnalysis.h
@@ -23,6 +23,7 @@
 #include "llvm/CodeGen/MachineFunctionPass.h"
 #include "llvm/CodeGen/LiveInterval.h"
 #include "llvm/ADT/BitVector.h"
+#include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/IndexedMap.h"
 
 namespace llvm {
@@ -30,6 +31,7 @@ namespace llvm {
   class LiveVariables;
   class MRegisterInfo;
   class TargetInstrInfo;
+  class TargetRegisterClass;
   class VirtRegMap;
 
   class LiveIntervals : public MachineFunctionPass {
@@ -56,6 +58,7 @@ namespace llvm {
     Reg2RegMap r2rMap_;
 
     BitVector allocatableRegs_;
+    DenseMap<const TargetRegisterClass*, BitVector> allocatableRCRegs_;
 
     /// JoinedLIs - Keep track which register intervals have been coalesced
     /// with other intervals.
@@ -202,7 +205,7 @@ namespace llvm {
     /// CopyCoallesceInMBB - Coallsece copies in the specified MBB, putting
     /// copies that cannot yet be coallesced into the "TryAgain" list.
     void CopyCoallesceInMBB(MachineBasicBlock *MBB,
-                            std::vector<CopyRec> &TryAgain);
+                         std::vector<CopyRec> &TryAgain, bool PhysOnly = false);
 
     /// JoinCopy - Attempt to join intervals corresponding to SrcReg/DstReg,
     /// which are the src/dst of the copy instruction CopyMI.  This returns true
@@ -210,7 +213,8 @@ namespace llvm {
     /// to coallesce these this copy, due to register constraints.  It returns
     /// false if it is not currently possible to coallesce this interval, but
     /// it may be possible if other things get coallesced.
-    bool JoinCopy(MachineInstr *CopyMI, unsigned SrcReg, unsigned DstReg);
+    bool JoinCopy(MachineInstr *CopyMI, unsigned SrcReg, unsigned DstReg,
+                  bool PhysOnly = false);
     
     /// JoinIntervals - Attempt to join these two intervals.  On failure, this
     /// returns false.  Otherwise, if one of the intervals being joined is a