AMDGPU: Make skip threshold an option

[nhaehnle]

I assume you're planning to use this in some tests? Anyway, LGTM.

lib/Target/AMDGPU/SILowerControlFlow.cpp

78

You can put the initializer here instead of in the constructor.

[arsenm]

r276680

lib/Target/AMDGPU/SILowerControlFlow.cpp

78

The rest don't do this, and it's probably better to move them all at once if people decide this is better

lib/Target/AMDGPU/SILowerControlFlow.cpp

 #include "llvm/IR/Constants.h"
 
 using namespace llvm;
 
 #define DEBUG_TYPE "si-lower-control-flow"
 
 namespace {
 
+static cl::opt<unsigned> SkipThresholdFlag(
+  "amdgpu-skip-threshold",
+  cl::desc("Number of instructions before jumping over divergent control flow"),
+  cl::init(12), cl::Hidden);
+
 class SILowerControlFlow : public MachineFunctionPass {
 private:
-  static const unsigned SkipThreshold = 12;
-
   const SIRegisterInfo *TRI;
   const SIInstrInfo *TII;
+  unsigned SkipThreshold;
 
   bool shouldSkip(MachineBasicBlock *From, MachineBasicBlock *To);
 
   void Skip(MachineInstr &From, MachineOperand &To);
   bool skipIfDead(MachineInstr &MI, MachineBasicBlock &NextBB);
 
   void If(MachineInstr &MI);
   void Else(MachineInstr &MI, bool ExecModified);
   void Break(MachineInstr &MI);
   void IfBreak(MachineInstr &MI);
   void ElseBreak(MachineInstr &MI);
   void Loop(MachineInstr &MI);
   void EndCf(MachineInstr &MI);
 
   void Kill(MachineInstr &MI);
   void Branch(MachineInstr &MI);
 
   MachineBasicBlock *insertSkipBlock(MachineBasicBlock &MBB,
                                      MachineBasicBlock::iterator I) const;
 public:
   static char ID;
 
   SILowerControlFlow() :
-    MachineFunctionPass(ID), TRI(nullptr), TII(nullptr) { }
+    MachineFunctionPass(ID), TRI(nullptr), TII(nullptr), SkipThreshold(0) { }
 
   bool runOnMachineFunction(MachineFunction &MF) override;
 
   const char *getPassName() const override {
     return "SI Lower control flow pseudo instructions";
   }
 };
 
MachineBasicBlock *SILowerControlFlow::insertSkipBlock(
 
   return SkipBB;
 }
 
 bool SILowerControlFlow::runOnMachineFunction(MachineFunction &MF) {
   const SISubtarget &ST = MF.getSubtarget<SISubtarget>();
   TII = ST.getInstrInfo();
   TRI = &TII->getRegisterInfo();
+  SkipThreshold = SkipThresholdFlag;
 
   SIMachineFunctionInfo *MFI = MF.getInfo<SIMachineFunctionInfo>();
 
   bool HaveKill = false;
   bool NeedFlat = false;
   unsigned Depth = 0;
 
   MachineFunction::iterator NextBB;