[AMDGPU] Add a new pass to insert waitcnts. Leave under an option for testing.

Based on comments in https://reviews.llvm.org/D31161.

llvm-svn: 300023
diff --git a/llvm/lib/Target/AMDGPU/AMDGPU.h b/llvm/lib/Target/AMDGPU/AMDGPU.h
index 15c996b..6725fb3 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPU.h
+++ b/llvm/lib/Target/AMDGPU/AMDGPU.h
@@ -48,6 +48,7 @@
 FunctionPass *createSIFixSGPRCopiesPass();
 FunctionPass *createSIDebuggerInsertNopsPass();
 FunctionPass *createSIInsertWaitsPass();
+FunctionPass *createSIInsertWaitcntsPass();
 FunctionPass *createAMDGPUCodeGenPreparePass(const GCNTargetMachine *TM = nullptr);
 
 ModulePass *createAMDGPUAnnotateKernelFeaturesPass(const TargetMachine *TM = nullptr);
@@ -125,6 +126,9 @@
 void initializeSIInsertWaitsPass(PassRegistry&);
 extern char &SIInsertWaitsID;
 
+void initializeSIInsertWaitcntsPass(PassRegistry&);
+extern char &SIInsertWaitcntsID;
+
 void initializeAMDGPUUnifyDivergentExitNodesPass(PassRegistry&);
 extern char &AMDGPUUnifyDivergentExitNodesID;