Teach PHIElimination to split critical edges when -split-phi-edges is enabled.

Critical edges leading to a PHI node are split when the PHI source variable is
live out from the predecessor block. This help the coalescer eliminate more
PHI joins.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@86725 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 9 insertions, 0 deletions

diff --git a/lib/CodeGen/PHIElimination.h b/lib/CodeGen/PHIElimination.h
index 8a04f9d6ac..8188440c89 100644
--- a/lib/CodeGen/PHIElimination.h
+++ b/lib/CodeGen/PHIElimination.h
@@ -89,12 +89,21 @@ namespace llvm {
     ///
     void analyzePHINodes(const MachineFunction& Fn);
 
+    /// Split critical edges where necessary for good coalescer performance.
+    void SplitPHIEdges(MachineFunction &MF, MachineBasicBlock &MBB);
+
     /// isLiveOut - Determine if Reg is live out from MBB, when not
     /// considering PHI nodes. This means that Reg is either killed by
     /// a successor block or passed through one.
     bool isLiveOut(unsigned Reg, const MachineBasicBlock &MBB,
                    LiveVariables &LV);
 
+    /// SplitCriticalEdge - Split a critical edge from A to B by
+    /// inserting a new MBB. Update branches in A and PHI instructions
+    /// in B. Return the new block.
+    MachineBasicBlock *SplitCriticalEdge(MachineBasicBlock *A,
+                                         MachineBasicBlock *B);
+
     // FindCopyInsertPoint - Find a safe place in MBB to insert a copy from
     // SrcReg.  This needs to be after any def or uses of SrcReg, but before
     // any subsequent point where control flow might jump out of the basic