[opt-remark] Teach opt-remark how to emit "NOTE" arguments that use the loc of the original remark instead of the args own.

This is useful if one wants to emit a note explanation (in my case that we
couldn't find any values) but do not have any other source loc but the original
remark.

Author: gottesmm

include/swift/SIL/OptimizationRemark.h

@@ -41,6 +41,15 @@ struct ArgumentKeyKind {
     // diagnostic when emitting diagnostics. Do nothing special
     // along the backend path.
     Note,
+
+    // Assume that this is a note that should be emitted as a separate
+    // diagnostic but that doesn't have its own source loc: we should reuse the
+    // one for the original remark.
+    //
+    // This is intended to be used in situations where one needs to emit a
+    // "note" warning due to us not being able to infer a part of our
+    // opt-remark.
+    ParentLocNote,
   };
 
   InnerTy innerValue;
@@ -60,6 +69,7 @@ struct ArgumentKeyKind {
     case InnerTy::Default:
       return false;
     case InnerTy::Note:
+    case InnerTy::ParentLocNote:
       return true;
     }
 

lib/SIL/Utils/OptimizationRemark.cpp

@@ -209,23 +209,26 @@ static void emitRemark(SILModule &module, const Remark<RemarkT> &remark,
   // If diagnostics are enabled, first emit the main diagnostic and then loop
   // through our arguments and allow the arguments to add additional diagnostics
   // if they want.
-  if (diagEnabled) {
-    auto &Diags = module.getASTContext().Diags;
-    Diags.diagnose(remark.getLocation(), id,
-                   remark.getMsg());
-    for (auto &arg : remark.getArgs()) {
-      switch (arg.key.kind) {
-      case ArgumentKeyKind::Default:
-        continue;
-      case ArgumentKeyKind::Note:
-        Diags.diagnose(arg.loc, diag::opt_remark_note,
-                       arg.key.data);
-        continue;
-      }
-
-      llvm_unreachable("Unhandled case?!");
-    }
-  }
+  if (!diagEnabled)
+    return;
+
+  auto &de = module.getASTContext().Diags;
+  de.diagnoseWithNotes(
+      de.diagnose(remark.getLocation(), id, remark.getMsg()), [&]() {
+        for (auto &arg : remark.getArgs()) {
+          switch (arg.key.kind) {
+          case ArgumentKeyKind::Default:
+            continue;
+          case ArgumentKeyKind::Note:
+            de.diagnose(arg.loc, diag::opt_remark_note, arg.val);
+            continue;
+          case ArgumentKeyKind::ParentLocNote:
+            de.diagnose(remark.getLocation(), diag::opt_remark_note, arg.val);
+            continue;
+          }
+          llvm_unreachable("Unhandled case?!");
+        }
+      });
 }
 
 void Emitter::emit(const RemarkPassed &remark) {