[Closure Specializer] check in a pass to specialize closure.

If we have function A calls function B with a closure C
func A {
  B(...) {
    // closure C
  }
}
and the inliner decides to not inline B into A, it may be beneficial to generate
a specialized version of B to have
func A {
  B_spec_with_C(..., arguments_to_closure_C)
}
 
SILCombine will optimize apply of partial_apply that are both in B_spec_with_C.
Then inliner can inline the closure to B_spec_with_C.

For profitability, we check the relative size of the callee B and the closure C.
We also check hotness of the callsite to B in A and callsites to the closure
inside B. For now, if closure is called inside a loop, we think it is
profitable.

I will add this to the pass manager in a follow-up patch.
rdar://16569736


Swift SVN r21216

tools/sil-opt/SILOpt.cpp

@@ -80,6 +80,7 @@ enum class PassKind {
   GlobalLoadStoreOpts,
   ArrayOpts,
   ABCOpts,
+  ClosureSpecialization
 };
 
 enum class OptGroup {
@@ -264,6 +265,9 @@ Passes(llvm::cl::desc("Passes:"),
                         clEnumValN(PassKind::ABCOpts,
                                    "abcopts",
                                    "Array bounds check opts."),
+                        clEnumValN(PassKind::ClosureSpecialization,
+                                   "closure-specialize",
+                                   "Closure specialization."),
                         clEnumValEnd));
 
 static llvm::cl::opt<bool>
@@ -464,6 +468,9 @@ static void runCommandLineSelectedPasses(SILModule *Module,
     case PassKind::ABCOpts:
       PM.add(createABCOpt());
       break;
+    case PassKind::ClosureSpecialization:
+      PM.add(createClosureSpecializer());
+      break;
     }
   }
   PM.run();