PR25890: Fix incoherent error handling in PerformImplicitConversion and

CheckSingleAssignmentConstraints. These no longer produce ExprError() when they
have not emitted an error, and reliably inform the caller when they *have*
emitted an error.

This fixes some serious issues where we would fail to emit any diagnostic for
invalid code and then attempt to emit code for an invalid AST, and conversely
some issues where we would emit two diagnostics for the same problem.

llvm-svn: 283508

1 files changed, 9 insertions, 7 deletions

diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index e47f35528f6..76877e1f2f9 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -7793,6 +7793,10 @@ Sema::CheckSingleAssignmentConstraints(QualType LHSType, ExprResult &CallerRHS,
                                        bool Diagnose,
                                        bool DiagnoseCFAudited,
                                        bool ConvertRHS) {
+  // We need to be able to tell the caller whether we diagnosed a problem, if
+  // they ask us to issue diagnostics.
+  assert((ConvertRHS || !Diagnose) && "can't indicate whether we diagnosed");
+
   // If ConvertRHS is false, we want to leave the caller's RHS untouched. Sadly,
   // we can't avoid *all* modifications at the moment, so we need some somewhere
   // to put the updated value.
@@ -7804,9 +7808,9 @@ Sema::CheckSingleAssignmentConstraints(QualType LHSType, ExprResult &CallerRHS,
       // C++ 5.17p3: If the left operand is not of class type, the
       // expression is implicitly converted (C++ 4) to the
       // cv-unqualified type of the left operand.
-      ExprResult Res;
+      QualType RHSType = RHS.get()->getType();
       if (Diagnose) {
-        Res = PerformImplicitConversion(RHS.get(), LHSType.getUnqualifiedType(),
+        RHS = PerformImplicitConversion(RHS.get(), LHSType.getUnqualifiedType(),
                                         AA_Assigning);
       } else {
         ImplicitConversionSequence ICS =
@@ -7818,17 +7822,15 @@ Sema::CheckSingleAssignmentConstraints(QualType LHSType, ExprResult &CallerRHS,
                                   /*AllowObjCWritebackConversion=*/false);
         if (ICS.isFailure())
           return Incompatible;
-        Res = PerformImplicitConversion(RHS.get(), LHSType.getUnqualifiedType(),
+        RHS = PerformImplicitConversion(RHS.get(), LHSType.getUnqualifiedType(),
                                         ICS, AA_Assigning);
       }
-      if (Res.isInvalid())
+      if (RHS.isInvalid())
         return Incompatible;
       Sema::AssignConvertType result = Compatible;
       if (getLangOpts().ObjCAutoRefCount &&
-          !CheckObjCARCUnavailableWeakConversion(LHSType,
-                                                 RHS.get()->getType()))
+          !CheckObjCARCUnavailableWeakConversion(LHSType, RHSType))
         result = IncompatibleObjCWeakRef;
-      RHS = Res;
       return result;
     }