[PATCH] D98798: Produce waring for performing pointer arithmetic on a null pointer.

[Jamie Schmeiser via Phabricator via cfe-commits]

jamieschmeiser created this revision.
jamieschmeiser added a reviewer: andrew.w.kaylor.
jamieschmeiser requested review of this revision.
Herald added a project: clang.

Test and produce warning for subtracting a pointer from null or subtracting null from a pointer.  Reuse existing warning that this is undefined behaviour.  Also add unit test for both warnings.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D98798

Files:
  clang/lib/Sema/SemaExpr.cpp
  clang/test/Sema/pointer-addition.c


Index: clang/test/Sema/pointer-addition.c
===================================================================
--- clang/test/Sema/pointer-addition.c
+++ clang/test/Sema/pointer-addition.c
@@ -29,4 +29,6 @@
   // Cases that don't match the GNU inttoptr idiom get a different warning.
   f = (char*)0 - i; // expected-warning {{performing pointer arithmetic on a null pointer has undefined behavior}}
   int *g = (int*)0 + i; // expected-warning {{performing pointer arithmetic on a null pointer has undefined behavior}}
+  f = (char*)((char*)0 - f); // expected-warning {{performing pointer arithmetic on a null pointer has undefined behavior}}
+  f = (char*)(f - (char*)0); // expected-warning {{performing pointer arithmetic on a null pointer has undefined behavior}}
 }
Index: clang/lib/Sema/SemaExpr.cpp
===================================================================
--- clang/lib/Sema/SemaExpr.cpp
+++ clang/lib/Sema/SemaExpr.cpp
@@ -10720,7 +10720,15 @@
                                                LHS.get(), RHS.get()))
         return QualType();
 
-      // FIXME: Add warnings for nullptr - ptr.
+      // Subtracting from a null pointer should produce a warning.
+      if (LHS.get()->IgnoreParenCasts()->isNullPointerConstant(Context,
+                                           Expr::NPC_ValueDependentIsNotNull))
+        diagnoseArithmeticOnNullPointer(*this, Loc, LHS.get(), false);
+
+      // Subtracting a null pointer should produce a warning.
+      if (RHS.get()->IgnoreParenCasts()->isNullPointerConstant(Context,
+                                           Expr::NPC_ValueDependentIsNotNull))
+        diagnoseArithmeticOnNullPointer(*this, Loc, RHS.get(), false);
 
       // The pointee type may have zero size.  As an extension, a structure or
       // union may have zero size or an array may have zero length.  In this


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D98798.331314.patch
Type: text/x-patch
Size: 1857 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/cfe-commits/attachments/20210317/92a627dd/attachment.bin>