[PATCH] Fix to PR5683 - issue diagnostic for pointer subtraction with type of size zero.

[Serge Pavlov]

sepavloff added you to the CC list for the revision "Fix to PR5683 - issue diagnostic for pointer subtraction with type of size zero.".

Hi rsmith,

http://llvm-reviews.chandlerc.com/D637

Files:
  include/clang/Basic/DiagnosticSemaKinds.td
  lib/Sema/SemaExpr.cpp
  test/Sema/empty1.c

Index: include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- include/clang/Basic/DiagnosticSemaKinds.td
+++ include/clang/Basic/DiagnosticSemaKinds.td
@@ -4243,6 +4243,9 @@
 def err_typecheck_sub_ptr_compatible : Error<
   "%diff{$ and $ are not pointers to compatible types|"
   "pointers to incompatible types}0,1">;
+def err_sub_ptr_zero_size_types : Error<
+  "subtraction of pointers to types of zero length (%diff{$ and $)|}0,1 "
+  "is not allowed">;
 def ext_typecheck_ordered_comparison_of_pointer_integer : ExtWarn<
   "ordered comparison between pointer and integer (%0 and %1)">;
 def ext_typecheck_ordered_comparison_of_pointer_and_zero : Extension<
Index: lib/Sema/SemaExpr.cpp
===================================================================
--- lib/Sema/SemaExpr.cpp
+++ lib/Sema/SemaExpr.cpp
@@ -6728,6 +6728,16 @@
           diagnosePointerIncompatibility(*this, Loc, LHS.get(), RHS.get());
           return QualType();
         }
+
+        // If pointee type is a structure or union of zero size (GCC extension),
+        // the subtraction does not have a sense.
+        CharUnits ElementSize = Context.getTypeSizeInChars(rpointee);
+        if (ElementSize.isZero() && rpointee.getTypePtr()->isStructureType()) {
+            Diag(Loc,diag::err_sub_ptr_zero_size_types)
+                << lpointee << rpointee
+                << LHS.get()->getSourceRange() << RHS.get()->getSourceRange();
+            return QualType();
+        }
       }
 
       if (!checkArithmeticBinOpPointerOperands(*this, Loc,
Index: test/Sema/empty1.c
===================================================================
--- /dev/null
+++ test/Sema/empty1.c
@@ -0,0 +1,33 @@
+// RUN: %clang_cc1 %s -fsyntax-only -verify
+
+struct empty {};
+struct empty_2 {};
+
+struct empty* func_1p (struct empty* x) {
+  return x - 5;
+}
+
+int func_1 () {
+  struct empty v[1];
+  return v - v;  // expected-error {{subtraction of pointers to types of zero length ('struct empty' and 'struct empty') is not allowed}}
+}
+
+int func_2 (struct empty* x) {
+  return 1 + x - x;  // expected-error {{subtraction of pointers to types of zero length ('struct empty' and 'struct empty') is not allowed}}
+}
+
+int func_3 (struct empty* x, struct empty* y) {
+  return x - y;  // expected-error {{subtraction of pointers to types of zero length ('struct empty' and 'struct empty') is not allowed}}
+}
+
+int func_4 (struct empty* x, const struct empty* y) {
+  return x - y;  // expected-error {{subtraction of pointers to types of zero length ('struct empty' and 'const struct empty') is not allowed}}
+}
+
+int func_5 (volatile struct empty* x, const struct empty* y) {
+  return x - y;  // expected-error {{subtraction of pointers to types of zero length ('volatile struct empty' and 'const struct empty') is not allowed}}
+}
+
+int func_6 (struct empty* x, struct empty_2* y) {
+  return x - y;  // expected-error {{'struct empty *' and 'struct empty_2 *' are not pointers to compatible types}}
+}
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