Add special case for function types

Author: vvuksanovic

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -3684,10 +3684,9 @@ def warn_alloca_align_alignof : Warning<
   "second argument to __builtin_alloca_with_align is supposed to be in bits">,
   InGroup<DiagGroup<"alloca-with-align-alignof">>;
 
-def warn_alloc_size
-    : Warning<
-          "allocation of insufficient size '%0' for type %1 with size '%2'">,
-      InGroup<DiagGroup<"alloc-size">>;
+def warn_alloc_size : Warning<
+  "allocation of insufficient size '%0' for type %1 with size '%2'">,
+  InGroup<DiagGroup<"alloc-size">>;
 
 def err_alignment_too_small : Error<
   "requested alignment must be %0 or greater">;

clang/lib/Sema/SemaExpr.cpp

@@ -7842,7 +7842,11 @@ static void CheckSufficientAllocSize(Sema &S, QualType DestType,
   auto Size = CharUnits::fromQuantity(AllocSize->getZExtValue());
 
   QualType TargetType = DestType->getPointeeType();
-  auto LhsSize = S.Context.getTypeSizeInCharsIfKnown(TargetType);
+  // Find the destination size. As a special case function types have size of
+  // one byte to match the sizeof operator behavior.
+  auto LhsSize = TargetType->isFunctionType()
+                     ? CharUnits::One()
+                     : S.Context.getTypeSizeInCharsIfKnown(TargetType);
   if (LhsSize && Size < LhsSize)
     S.Diag(E->getExprLoc(), diag::warn_alloc_size)
         << Size.getQuantity() << TargetType << LhsSize->getQuantity();

clang/test/Sema/warn-alloc-size.c

@@ -43,5 +43,7 @@ void alloc_foo(void) {
   (void)(int *)my_malloc(1);                              // expected-warning {{allocation of insufficient size '1' for type 'int' with size '4'}}
 
   struct ZeroSize *ptr18 = my_malloc(0); // okay becuase sizeof(struct ZeroSize) = 0
-                                         // allocation of size 0 is implementation defined behavior though
+
+  void *funcptr_1 = (void (*)(int))my_malloc(0); // expected-warning {{allocation of insufficient size '0' for type 'void (int)' with size '1'}}
+  void *funcptr_2 = (void (*)(int))my_malloc(1);
 }