Be more clever about calculating live variables through new basic blocks.

When splitting a critical edge, the registers live through the edge are:

- Used in a PHI instruction, or
- Live out from the predecessor, and
- Live in to the successor.

This allows the coalescer to eliminate even more phi joins.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@89530 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 18 insertions, 5 deletions

diff --git a/include/llvm/CodeGen/LiveVariables.h b/include/llvm/CodeGen/LiveVariables.h
index b2be569bc1..a37abd4645 100644
--- a/include/llvm/CodeGen/LiveVariables.h
+++ b/include/llvm/CodeGen/LiveVariables.h
@@ -107,6 +107,13 @@ public:
     /// findKill - Find a kill instruction in MBB. Return NULL if none is found.
     MachineInstr *findKill(const MachineBasicBlock *MBB) const;
 
+    /// isLiveIn - Is Reg live in to MBB? This means that Reg is live through
+    /// MBB, or it is killed in MBB. If Reg is only used by PHI instructions in
+    /// MBB, it is not considered live in.
+    bool isLiveIn(const MachineBasicBlock &MBB,
+                  unsigned Reg,
+                  MachineRegisterInfo &MRI);
+
     void dump() const;
   };
 
@@ -267,11 +274,17 @@ public:
   void HandleVirtRegUse(unsigned reg, MachineBasicBlock *MBB,
                         MachineInstr *MI);
 
-  /// addNewBlock - Add a new basic block BB as an empty succcessor to
-  /// DomBB. All variables that are live out of DomBB will be marked as passing
-  /// live through BB. This method assumes that the machine code is still in SSA
-  /// form.
-  void addNewBlock(MachineBasicBlock *BB, MachineBasicBlock *DomBB);
+  bool isLiveIn(unsigned Reg, const MachineBasicBlock &MBB) {
+    return getVarInfo(Reg).isLiveIn(MBB, Reg, *MRI);
+  }
+
+  /// addNewBlock - Add a new basic block BB between DomBB and SuccBB. All
+  /// variables that are live out of DomBB and live into SuccBB will be marked
+  /// as passing live through BB. This method assumes that the machine code is
+  /// still in SSA form.
+  void addNewBlock(MachineBasicBlock *BB,
+                   MachineBasicBlock *DomBB,
+                   MachineBasicBlock *SuccBB);
 };
 
 } // End llvm namespace