SILVerifier: print a readable error message when referencing an undefined SIL function

This error was not printed because the verifier complained before the error handling was done.

Author: eeckstein

lib/SIL/Parser/ParseSIL.cpp

@@ -70,16 +70,6 @@ ParseIncompleteOSSA("parse-incomplete-ossa",
 //===----------------------------------------------------------------------===//
 
 SILParserState::~SILParserState() {
-  if (!ForwardRefFns.empty()) {
-    for (auto Entry : ForwardRefFns) {
-      if (Entry.second.Loc.isValid()) {
-        M.getASTContext().Diags.diagnose(Entry.second.Loc,
-                                         diag::sil_use_of_undefined_value,
-                                         Entry.first.str());
-      }
-    }
-  }
-
   // Turn any debug-info-only function declarations into zombies.
   markZombies();
 }
@@ -93,6 +83,21 @@ void SILParserState::markZombies() {
   }
 }
 
+bool SILParserState::diagnoseUndefinedValues(DiagnosticEngine &diags) {
+  bool hasError = false;
+  if (!ForwardRefFns.empty()) {
+    for (auto Entry : ForwardRefFns) {
+      if (Entry.second.Loc.isValid()) {
+        diags.diagnose(Entry.second.Loc,
+                       diag::sil_use_of_undefined_value,
+                       Entry.first.str());
+        hasError = true;
+      }
+    }
+  }
+  return hasError;
+}
+
 std::unique_ptr<SILModule>
 ParseSILModuleRequest::evaluate(Evaluator &evaluator,
                                 ASTLoweringDescriptor desc) const {
@@ -111,6 +116,10 @@ ParseSILModuleRequest::evaluate(Evaluator &evaluator,
   }
 
   auto hadError = parser.parseTopLevelSIL();
+
+  if (parserState.diagnoseUndefinedValues(parser.Diags))
+    hadError = true;
+
   if (hadError) {
     // The rest of the SIL pipeline expects well-formed SIL, so if we encounter
     // a parsing error, just return an empty SIL module.

lib/SIL/Parser/SILParserState.h

@@ -51,6 +51,8 @@ class SILParserState : public SILParserStateBase {
   /// Did we parse a sil_stage for this module?
   bool DidParseSILStage = false;
 
+  bool diagnoseUndefinedValues(DiagnosticEngine &diags);
+
   bool parseDeclSIL(Parser &P) override;
   bool parseDeclSILStage(Parser &P) override;
   bool parseSILVTable(Parser &P) override;

test/SIL/verifier-undefined-function.sil

@@ -0,0 +1,16 @@
+// RUN: not %target-sil-opt -o /dev/null %s 2>&1 | %FileCheck %s
+
+// REQUIRES: asserts
+
+sil_stage canonical
+
+import Builtin
+
+sil  @undefined_function_ref : $@convention(thin) () -> () {
+bb0:
+  // CHECK:  :[[@LINE+1]]:21: error: use of undefined value 'undefined_function'
+  %0 = function_ref @undefined_function : $@convention(thin) () -> ()
+  %r = tuple ()
+  return %r
+}
+