[Diagnostics] Teach -Wnull-dereference about address_space attribute

Summary:
Clang should not warn for:

> test.c:2:12: warning: indirection of non-volatile null pointer will be deleted,
>       not trap [-Wnull-dereference]
>     return *(int __attribute__((address_space(256))) *) 0;
>            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Solves PR42292.

Reviewers: aaron.ballman, rsmith

Reviewed By: aaron.ballman

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D69664

Author: davidbolvansky

clang/lib/Sema/SemaExpr.cpp

@@ -481,16 +481,21 @@ static void CheckForNullPointerDereference(Sema &S, Expr *E) {
   // optimizer will delete, so warn about it.  People sometimes try to use this
   // to get a deterministic trap and are surprised by clang's behavior.  This
   // only handles the pattern "*null", which is a very syntactic check.
-  if (UnaryOperator *UO = dyn_cast<UnaryOperator>(E->IgnoreParenCasts()))
-    if (UO->getOpcode() == UO_Deref &&
-        UO->getSubExpr()->IgnoreParenCasts()->
-          isNullPointerConstant(S.Context, Expr::NPC_ValueDependentIsNotNull) &&
+  const auto *UO = dyn_cast<UnaryOperator>(E->IgnoreParenCasts());
+  if (UO && UO->getOpcode() == UO_Deref) {
+    const LangAS AS =
+        UO->getSubExpr()->getType()->getPointeeType().getAddressSpace();
+    if ((!isTargetAddressSpace(AS) ||
+         (isTargetAddressSpace(AS) && toTargetAddressSpace(AS) == 0)) &&
+        UO->getSubExpr()->IgnoreParenCasts()->isNullPointerConstant(
+            S.Context, Expr::NPC_ValueDependentIsNotNull) &&
         !UO->getType().isVolatileQualified()) {
-    S.DiagRuntimeBehavior(UO->getOperatorLoc(), UO,
-                          S.PDiag(diag::warn_indirection_through_null)
-                            << UO->getSubExpr()->getSourceRange());
-    S.DiagRuntimeBehavior(UO->getOperatorLoc(), UO,
-                        S.PDiag(diag::note_indirection_through_null));
+      S.DiagRuntimeBehavior(UO->getOperatorLoc(), UO,
+                            S.PDiag(diag::warn_indirection_through_null)
+                                << UO->getSubExpr()->getSourceRange());
+      S.DiagRuntimeBehavior(UO->getOperatorLoc(), UO,
+                            S.PDiag(diag::note_indirection_through_null));
+    }
   }
 }
 

clang/test/Sema/exprs.c

@@ -179,17 +179,27 @@ void test18(int b) {
   test18_e(); // expected-error {{too few arguments to function call, expected at least 2, have 0}}
 }
 
+typedef int __attribute__((address_space(256))) int_AS256;
 // PR7569
 void test19() {
-  *(int*)0 = 0;   // expected-warning {{indirection of non-volatile null pointer}} \
+  *(int *)0 = 0;                                     // expected-warning {{indirection of non-volatile null pointer}} \
                   // expected-note {{consider using __builtin_trap}}
-  *(volatile int*)0 = 0;  // Ok.
+  *(volatile int *)0 = 0;                            // Ok.
+  *(int __attribute__((address_space(256))) *)0 = 0; // Ok.
+  *(int __attribute__((address_space(0))) *)0 = 0;   // expected-warning {{indirection of non-volatile null pointer}} \
+                     // expected-note {{consider using __builtin_trap}}
+  *(int_AS256 *)0 = 0;                               // Ok.
 
   // rdar://9269271
-  int x = *(int*)0;  // expected-warning {{indirection of non-volatile null pointer}} \
+  int x = *(int *)0;                                                                          // expected-warning {{indirection of non-volatile null pointer}} \
+                     // expected-note {{consider using __builtin_trap}}
+  int x2 = *(volatile int *)0;                                                                // Ok.
+  int x3 = *(int __attribute__((address_space(0))) *)0;                                       // expected-warning {{indirection of non-volatile null pointer}} \
                      // expected-note {{consider using __builtin_trap}}
-  int x2 = *(volatile int*)0; // Ok.
-  int *p = &(*(int*)0); // Ok;
+  int x4 = *(int_AS256 *)0;                                                                   // Ok.
+  int *p = &(*(int *)0);                                                                      // Ok.
+  int_AS256 *p1 = &(*(int __attribute__((address_space(256))) *)0);                           // Ok.
+  int __attribute__((address_space(0))) *p2 = &(*(int __attribute__((address_space(0))) *)0); // Ok.
 }
 
 int test20(int x) {