[Sema] Teach overload resolution about unaddressable functions.

Given an expression like `(&Foo)();`, we perform overload resolution as
if we are calling `Foo` directly. This causes problems if `Foo` is a
function that can't have its address taken. This patch teaches overload
resolution to ignore functions that can't have their address taken in
such cases.

Differential Revision: http://reviews.llvm.org/D15590

llvm-svn: 257016

2 files changed, 39 insertions, 4 deletions

diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 8e50d5a103c..67d5db15cf2 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -4935,7 +4935,9 @@ Sema::ActOnCallExpr(Scope *S, Expr *Fn, SourceLocation LParenLoc,
       OverloadExpr *ovl = find.Expression;
       if (UnresolvedLookupExpr *ULE = dyn_cast<UnresolvedLookupExpr>(ovl))
         return BuildOverloadedCallExpr(S, Fn, ULE, LParenLoc, ArgExprs,
-                                       RParenLoc, ExecConfig);
+                                       RParenLoc, ExecConfig,
+                                       /*AllowTypoCorrection=*/true,
+                                       find.IsAddressOfOperand);
       return BuildCallToMemberFunction(S, Fn, LParenLoc, ArgExprs, RParenLoc);
     }
   }
@@ -4949,10 +4951,14 @@ Sema::ActOnCallExpr(Scope *S, Expr *Fn, SourceLocation LParenLoc,
 
   Expr *NakedFn = Fn->IgnoreParens();
 
+  bool CallingNDeclIndirectly = false;
   NamedDecl *NDecl = nullptr;
-  if (UnaryOperator *UnOp = dyn_cast<UnaryOperator>(NakedFn))
-    if (UnOp->getOpcode() == UO_AddrOf)
+  if (UnaryOperator *UnOp = dyn_cast<UnaryOperator>(NakedFn)) {
+    if (UnOp->getOpcode() == UO_AddrOf) {
+      CallingNDeclIndirectly = true;
       NakedFn = UnOp->getSubExpr()->IgnoreParens();
+    }
+  }
 
   if (isa<DeclRefExpr>(NakedFn)) {
     NDecl = cast<DeclRefExpr>(NakedFn)->getDecl();
@@ -4974,6 +4980,11 @@ Sema::ActOnCallExpr(Scope *S, Expr *Fn, SourceLocation LParenLoc,
     NDecl = cast<MemberExpr>(NakedFn)->getMemberDecl();
 
   if (FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(NDecl)) {
+    if (CallingNDeclIndirectly &&
+        !checkAddressOfFunctionIsAvailable(FD, /*Complain=*/true,
+                                           Fn->getLocStart()))
+      return ExprError();
+
     if (FD->hasAttr<EnableIfAttr>()) {
       if (const EnableIfAttr *Attr = CheckEnableIf(FD, ArgExprs, true)) {
         Diag(Fn->getLocStart(),
diff --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp
index e0c10e4479e..682f3692bac 100644
--- a/clang/lib/Sema/SemaOverload.cpp
+++ b/clang/lib/Sema/SemaOverload.cpp
@@ -9643,6 +9643,13 @@ static void NoteFunctionCandidate(Sema &S, OverloadCandidate *Cand,
 
   case ovl_fail_enable_if:
     return DiagnoseFailedEnableIfAttr(S, Cand);
+
+  case ovl_fail_addr_not_available: {
+    bool Available = checkAddressOfCandidateIsAvailable(S, Cand->Function);
+    (void)Available;
+    assert(!Available);
+    break;
+  }
   }
 }
 
@@ -11245,6 +11252,17 @@ static ExprResult FinishOverloadedCallExpr(Sema &SemaRef, Scope *S, Expr *Fn,
   return ExprError();
 }
 
+static void markUnaddressableCandidatesUnviable(Sema &S,
+                                                OverloadCandidateSet &CS) {
+  for (auto I = CS.begin(), E = CS.end(); I != E; ++I) {
+    if (I->Viable &&
+        !S.checkAddressOfFunctionIsAvailable(I->Function, /*Complain=*/false)) {
+      I->Viable = false;
+      I->FailureKind = ovl_fail_addr_not_available;
+    }
+  }
+}
+
 /// BuildOverloadedCallExpr - Given the call expression that calls Fn
 /// (which eventually refers to the declaration Func) and the call
 /// arguments Args/NumArgs, attempt to resolve the function call down
@@ -11257,7 +11275,8 @@ ExprResult Sema::BuildOverloadedCallExpr(Scope *S, Expr *Fn,
                                          MultiExprArg Args,
                                          SourceLocation RParenLoc,
                                          Expr *ExecConfig,
-                                         bool AllowTypoCorrection) {
+                                         bool AllowTypoCorrection,
+                                         bool CalleesAddressIsTaken) {
   OverloadCandidateSet CandidateSet(Fn->getExprLoc(),
                                     OverloadCandidateSet::CSK_Normal);
   ExprResult result;
@@ -11266,6 +11285,11 @@ ExprResult Sema::BuildOverloadedCallExpr(Scope *S, Expr *Fn,
                              &result))
     return result;
 
+  // If the user handed us something like `(&Foo)(Bar)`, we need to ensure that
+  // functions that aren't addressible are considered unviable.
+  if (CalleesAddressIsTaken)
+    markUnaddressableCandidatesUnviable(*this, CandidateSet);
+
   OverloadCandidateSet::iterator Best;
   OverloadingResult OverloadResult =
       CandidateSet.BestViableFunction(*this, Fn->getLocStart(), Best);