[move-only] Emit a "checker did not understand" error if copy propagation fails for some reason.

We already emit a "checker did not understand" error if our pattern matching at
the beginning failed. This just tightens the logic even more by including
another potential error condition.

NOTE: This was caught by the SILVerifier check that copy_value in canonical SIL
can not take a move only type as an argument. Its better to catch this with a
nice earlier diagnostic though.

Author: gottesmm

lib/SILOptimizer/Mandatory/MoveOnlyObjectChecker.cpp

@@ -418,7 +418,24 @@ bool MoveOnlyChecker::check(NonLocalAccessBlockAnalysis *accessBlockAnalysis,
     LLVM_DEBUG(llvm::dbgs() << "Visiting: " << *markedValue);
 
     // First canonicalize ownership.
-    changed |= canonicalizer.canonicalizeValueLifetime(markedValue);
+    if (!canonicalizer.canonicalizeValueLifetime(markedValue)) {
+      // If we failed to canonicalize ownership, there was something in the SIL
+      // that copy propagation did not understand. Emit a we did not understand
+      // error.
+      if (markedValue->getType().isMoveOnlyWrapped()) {
+        diagnose(fn->getASTContext(), markedValue->getLoc().getSourceLoc(),
+                 diag::sil_moveonlychecker_not_understand_no_implicit_copy);
+      } else {
+        diagnose(fn->getASTContext(), markedValue->getLoc().getSourceLoc(),
+                 diag::sil_moveonlychecker_not_understand_moveonly);
+      }
+      valuesWithDiagnostics.insert(markedValue);
+      continue;
+    } else {
+      // Always set changed to true if we succeeded in canonicalizing since we
+      // may have rewritten copies.
+      changed = true;
+    }
 
     // If we are asked to perform guaranteed checking, emit an error if we have
     // /any/ consuming uses.
@@ -532,6 +549,9 @@ class MoveOnlyCheckerPass : public SILFunctionTransform {
     assert(fn->getModule().getStage() == SILStage::Raw &&
            "Should only run on Raw SIL");
 
+    LLVM_DEBUG(llvm::dbgs() << "===> MoveOnly Object Checker. Visiting: "
+                            << fn->getName() << '\n');
+
     auto *accessBlockAnalysis = getAnalysis<NonLocalAccessBlockAnalysis>();
     auto *dominanceAnalysis = getAnalysis<DominanceAnalysis>();
     DominanceInfo *domTree = dominanceAnalysis->get(fn);