[MacroFusion] Expose useful static methods. NFC.

[Joe_Nash]

Summary

hasLessThanNumFused and fuseInstructionPair are useful for
DAG mutations similar to MacroFusion, but which cannot use
MacroFusion as a whole (such as fusing non-dependent instruction).

[MatzeB]

LGTM with docu comments added.

llvm/include/llvm/CodeGen/MacroFusion.h

37–39

Please add some documentation when making the API available to more users!

[Joe_Nash]

add doc comment

[Joe_Nash]

Thanks. Adding the comment even gave me an idea for my client code :)

llvm/include/llvm/CodeGen/MacroFusion.h

 #include <memory>
 
 namespace llvm {
 
 class MachineInstr;
 class ScheduleDAGMutation;
 class TargetInstrInfo;
 class TargetSubtargetInfo;
+class ScheduleDAGInstrs;
+class SUnit;
 
 /// Check if the instr pair, FirstMI and SecondMI, should be fused
 /// together. Given SecondMI, when FirstMI is unspecified, then check if
 /// SecondMI may be part of a fused pair at all.
 using ShouldSchedulePredTy = std::function<bool(const TargetInstrInfo &TII,
                                                 const TargetSubtargetInfo &TSI,
                                                 const MachineInstr *FirstMI,
                                                 const MachineInstr &SecondMI)>;
 
+/// Checks if the number of cluster edges between SU and its predecessors is
+/// less than FuseLimit
+bool hasLessThanNumFused(const SUnit &SU, unsigned FuseLimit);
+
+/// Create an artificial edge between FirstSU and SecondSU.
+/// Make data dependencies from the FirstSU also dependent on the SecondSU to
+/// prevent them from being scheduled between the FirstSU and the SecondSU
+/// and vice-versa.
+/// Fusing more than 2 instructions is not currently supported.
+bool fuseInstructionPair(ScheduleDAGInstrs &DAG, SUnit &FirstSU,
+                         SUnit &SecondSU);
+
 /// Create a DAG scheduling mutation to pair instructions back to back
 /// for instructions that benefit according to the target-specific
 /// shouldScheduleAdjacent predicate function.
 std::unique_ptr<ScheduleDAGMutation>
 createMacroFusionDAGMutation(ShouldSchedulePredTy shouldScheduleAdjacent);
 
 /// Create a DAG scheduling mutation to pair branch instructions with one
 /// of their predecessors back to back for instructions that benefit according
 /// to the target-specific shouldScheduleAdjacent predicate function.
 std::unique_ptr<ScheduleDAGMutation>
 createBranchMacroFusionDAGMutation(ShouldSchedulePredTy shouldScheduleAdjacent);
 
 } // end namespace llvm
 
 #endif // LLVM_CODEGEN_MACROFUSION_H

llvm/lib/CodeGen/MacroFusion.cpp

 static SUnit *getPredClusterSU(const SUnit &SU) {
   for (const SDep &SI : SU.Preds)
     if (SI.isCluster())
       return SI.getSUnit();
 
   return nullptr;
 }
 
-static bool hasLessThanNumFused(const SUnit &SU, unsigned FuseLimit) {
+bool llvm::hasLessThanNumFused(const SUnit &SU, unsigned FuseLimit) {
   unsigned Num = 1;
   const SUnit *CurrentSU = &SU;
   while ((CurrentSU = getPredClusterSU(*CurrentSU)) && Num < FuseLimit) Num ++;
   return Num < FuseLimit;
 }
 
-static bool fuseInstructionPair(ScheduleDAGInstrs &DAG, SUnit &FirstSU,
-                                SUnit &SecondSU) {
+bool llvm::fuseInstructionPair(ScheduleDAGInstrs &DAG, SUnit &FirstSU,
   // Check that neither instr is already paired with another along the edge
   // between them.
   for (SDep &SI : FirstSU.Succs)
     if (SI.isCluster())
       return false;
 
   for (SDep &SI : SecondSU.Preds)
     if (SI.isCluster())