[opt-remark] Teach opt-remark how to emit remarks for retain/release of @_emptyArrayStorage.

This just involved teaching opt-remark-gen how to pattern match the following
SIL:

```
%0 = global_addr @_swiftEmptyArrayStorage : $*_SwiftEmptyArrayStorage
%1 = address_to_pointer %0 : $*_SwiftEmptyArrayStorage to $Builtin.RawPointer
%2 = raw_pointer_to_ref %1 : $Builtin.RawPointer to $__EmptyArrayStorage
```

Now we produce the following remark:

```
./swift/test/SILOptimizer/opt_remark/opt_remark_generator.sil:105:3: remark: retain of type 'EmptyArrayStorage'
  strong_retain %2 : $EmptyArrayStorage // expected-remark {{retain of type 'EmptyArrayStorage'}}
  ^
./swift/test/SILOptimizer/opt_remark/opt_remark_generator.sil:42:5: note: of 'swiftEmptyArrayStorage'
var swiftEmptyArrayStorage: _SwiftEmptyArrayStorage
    ^
```

Author: gottesmm

lib/SILOptimizer/Transforms/OptRemarkGenerator.cpp

@@ -28,6 +28,7 @@
 #include "swift/SIL/Projection.h"
 #include "swift/SIL/SILFunction.h"
 #include "swift/SIL/SILInstruction.h"
+#include "swift/SIL/PatternMatch.h"
 #include "swift/SIL/SILModule.h"
 #include "swift/SIL/SILVisitor.h"
 #include "swift/SILOptimizer/Analysis/RCIdentityAnalysis.h"
@@ -37,6 +38,7 @@
 #include "llvm/Support/raw_ostream.h"
 
 using namespace swift;
+using namespace swift::PatternMatch;
 
 static llvm::cl::opt<bool> ForceVisitImplicitAutogeneratedFunctions(
     "optremarkgen-visit-implicit-autogen-funcs", llvm::cl::Hidden,
@@ -374,6 +376,30 @@ bool ValueToDeclInferrer::infer(
       }
     }
 
+    // A pattern that we see around empty array storage is:
+    //
+    //   %0 = global_addr @_swiftEmptyArrayStorage : $*_SwiftEmptyArrayStorage
+    //   %1 = address_to_pointer %0 : $*_SwiftEmptyArrayStorage to $Builtin.RawPointer
+    //   %2 = raw_pointer_to_ref %1 : $Builtin.RawPointer to $__EmptyArrayStorage
+    //
+    // Recognize this case.
+    {
+      GlobalAddrInst *gai;
+      if (match(value, m_RawPointerToRefInst(
+                           m_AddressToPointerInst(m_GlobalAddrInst(gai))))) {
+        if (auto *decl = gai->getReferencedGlobal()->getDecl()) {
+          std::string msg;
+          {
+            llvm::raw_string_ostream stream(msg);
+            printNote(stream, decl);
+          }
+          resultingInferredDecls.push_back(
+              Argument({keyKind, "InferredValue"}, std::move(msg), decl));
+          return true;
+        }
+      }
+    }
+
     // We prefer decls not from uses since these are inherently noisier. Still,
     // it is better than nothing.
     bool foundDeclFromUse = false;

test/SILOptimizer/opt_remark/opt_remark_generator.sil

@@ -31,6 +31,14 @@ struct StructWithOwnerAndState {
   var state: TrivialState
 }
 
+struct _SwiftEmptyArrayStorage {
+  var nonTrivialField: Klass = Klass()
+}
+
+class EmptyArrayStorage {
+  var state: TrivialState = .first
+}
+
 ///////////
 // Tests //
 ///////////
@@ -84,3 +92,17 @@ bb0(%0 : $StructWithOwner, %1 : $TrivialState):
                             // expected-note @-3 {{of 'x'}}
   return %3 : $Klass
 }
+
+// Please keep these next to this test to make the note on the decl not far from its check.
+var swiftEmptyArrayStorage: _SwiftEmptyArrayStorage
+sil_global hidden @$s20opt_remark_generator22swiftEmptyArrayStorageAA06_SwiftefG0Vvp : $_SwiftEmptyArrayStorage
+
+sil @retainOnEmptyArrayStorage : $@convention(thin) () -> @owned EmptyArrayStorage {
+bb0:
+  %0 = global_addr @$s20opt_remark_generator22swiftEmptyArrayStorageAA06_SwiftefG0Vvp : $*_SwiftEmptyArrayStorage
+  %1 = address_to_pointer %0 : $*_SwiftEmptyArrayStorage to $Builtin.RawPointer
+  %2 = raw_pointer_to_ref %1 : $Builtin.RawPointer to $EmptyArrayStorage
+  strong_retain %2 : $EmptyArrayStorage // expected-remark {{retain of type 'EmptyArrayStorage'}}
+                                        // expected-note @-9 {{of 'swiftEmptyArrayStorage'}}
+  return %2 : $EmptyArrayStorage
+}