[opt-remark] Skip implicit top level functions and autogenerated compiler functions.

This eliminates opt-remarks on initializers/friends, e.x.:

```
struct KlassPair {
   var lhs: Klass // expected-remark {{retain of type 'Klass'}}
                  // expected-note @-1 {{of 'self.lhs'}}
                  // expected-remark @-2 {{release of type 'Klass'}}
                  // expected-note @-3 {{of 'self.lhs'}}
   var rhs: Klass // expected-remark {{retain of type 'Klass'}}
                  // expected-note @-1 {{of 'self.rhs'}}
                  // expected-remark @-2 {{release of type 'Klass'}}
                  // expected-note @-3 {{of 'self.rhs'}}
}
```

becomes:

```
struct KlassPair {
   var lhs: Klass
   var rhs: Klass
}
```

I also added an -Xllvm option (-optremarkgen-visit-implicit-autogen-funcs) that
will force these to be emitted as a compiler knob for compiler developers. There
is a test that validates the behavior.

Author: gottesmm

lib/SILOptimizer/Transforms/OptRemarkGenerator.cpp

@@ -30,10 +30,17 @@
 #include "swift/SILOptimizer/Analysis/RCIdentityAnalysis.h"
 #include "swift/SILOptimizer/PassManager/Passes.h"
 #include "swift/SILOptimizer/PassManager/Transforms.h"
+#include "llvm/Support/CommandLine.h"
 #include "llvm/Support/raw_ostream.h"
 
 using namespace swift;
 
+static llvm::cl::opt<bool> ForceVisitImplicitAutogeneratedFunctions(
+    "optremarkgen-visit-implicit-autogen-funcs", llvm::cl::Hidden,
+    llvm::cl::desc(
+        "Emit opt remarks even on implicit and autogenerated functions"),
+    llvm::cl::init(false));
+
 //===----------------------------------------------------------------------===//
 //                                  Utility
 //===----------------------------------------------------------------------===//
@@ -347,6 +354,21 @@ class OptRemarkGenerator : public SILFunctionTransform {
       return;
 
     auto *fn = getFunction();
+
+    // Skip top level implicit functions and top level autogenerated functions,
+    // unless we were asked by the user to emit them.
+    if (!ForceVisitImplicitAutogeneratedFunctions) {
+      // Skip implicit functions generated by Sema.
+      if (auto *ctx = fn->getDeclContext())
+        if (auto *decl = ctx->getAsDecl())
+          if (decl->isImplicit())
+            return;
+      // Skip autogenerated functions generated by SILGen.
+      if (auto loc = fn->getDebugScope()->getLoc())
+        if (loc.isAutoGenerated())
+          return;
+    }
+
     LLVM_DEBUG(llvm::dbgs() << "Visiting: " << fn->getName() << "\n");
     auto &rcfi = *getAnalysis<RCIdentityAnalysis>()->get(fn);
     OptRemarkGeneratorInstructionVisitor visitor(*fn, rcfi);

test/SILOptimizer/opt-remark-generator-force-emit-implicit-autogen.swift

@@ -0,0 +1,15 @@
+// RUN: %target-swiftc_driver -O -Rpass-missed=sil-opt-remark-gen -Xllvm -sil-disable-pass=FunctionSignatureOpts -emit-sil %s -o /dev/null -Xfrontend -verify -Xllvm -optremarkgen-visit-implicit-autogen-funcs=1
+
+class Klass {}
+
+struct KlassPair {
+    var lhs: Klass // expected-remark {{retain of type 'Klass'}}
+                   // expected-note @-1 {{of 'self.lhs'}}
+                   // expected-remark @-2 {{release of type 'Klass'}}
+                   // expected-note @-3 {{of 'self.lhs'}}
+    var rhs: Klass // expected-remark {{retain of type 'Klass'}}
+                   // expected-note @-1 {{of 'self.rhs'}}
+                   // expected-remark @-2 {{release of type 'Klass'}}
+                   // expected-note @-3 {{of 'self.rhs'}}
+}
+

test/SILOptimizer/opt-remark-generator.swift

@@ -31,13 +31,7 @@ case third
 }
 
 struct StructWithOwner {
-    // This retain is from the initializers of owner.
-    //
-    // TODO: Should we emit this?
-    var owner = Klass() // expected-remark {{retain of type 'Klass'}}
-                        // expected-note @-1 {{of 'self.owner'}}
-                        // expected-remark @-2 {{release of type 'Klass'}}
-                        // expected-note @-3 {{of 'self.owner'}}
+    var owner = Klass()
     var state = TrivialState.first
 }
 
@@ -66,14 +60,8 @@ func callingAnInitializerStructWithOwner(x: Klass) -> StructWithOwner {
 }
 
 struct KlassPair {
-    var lhs: Klass // expected-remark {{retain of type 'Klass'}}
-                   // expected-note @-1 {{of 'self.lhs'}}
-                   // expected-remark @-2 {{release of type 'Klass'}}
-                   // expected-note @-3 {{of 'self.lhs'}}
-    var rhs: Klass // expected-remark {{retain of type 'Klass'}}
-                   // expected-note @-1 {{of 'self.rhs'}}
-                   // expected-remark @-2 {{release of type 'Klass'}}
-                   // expected-note @-3 {{of 'self.rhs'}}
+    var lhs: Klass
+    var rhs: Klass
 }
 
 func printKlassPair(x : KlassPair) {