c++: Ignore __sanitizer_ptr_{sub,cmp} builtin calls during constant expression evalua...

These two builtin calls are added already during parsing before pointer
subtractions or comparisons, normally they perform runtime verification
of whether the pointers point to the same object or different objects,
but during constant expressione valuation we don't really need those
builtins for anything.

2020-09-22  Jakub Jelinek  <jakub@redhat.com>

	PR c++/97145
	* constexpr.c (cxx_eval_builtin_function_call): Return void_node for
	calls to __sanitize_ptr_{sub,cmp} builtins.

	* g++.dg/asan/pr97145.C: New test.

(cherry picked from commit bc13106e0414b86af8f6878e7681e6a959921b9e)

diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index 8145558c8caf5ef59322cce4dfaa34b71adbfebf..8ecff36942561c6fb16747dcc7f5cb3b23c84b62 100644 (file)
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -1301,6 +1301,12 @@ cxx_eval_builtin_function_call (const constexpr_ctx *ctx, tree t, tree fun,
       case BUILT_IN_STRSTR:
        strops = 2;
        strret = 1;
+       break;
+      case BUILT_IN_ASAN_POINTER_COMPARE:
+      case BUILT_IN_ASAN_POINTER_SUBTRACT:
+       /* These builtins shall be ignored during constant expression
+          evaluation.  */
+       return void_node;
       default:
        break;
       }

diff --git a/gcc/testsuite/g++.dg/asan/pr97145.C b/gcc/testsuite/g++.dg/asan/pr97145.C
new file mode 100644 (file)
index 0000000..993c8a5
--- /dev/null
+++ b/gcc/testsuite/g++.dg/asan/pr97145.C
@@ -0,0 +1,7 @@
+// PR c++/97145
+// { dg-do compile { target c++11 } }
+// { dg-options "-fsanitize=address,pointer-subtract,pointer-compare" }
+
+constexpr char *a = nullptr;
+constexpr auto b = a - a;
+constexpr auto c = a < a;