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.

diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index 72fbdab..dacce58 100644 (file)
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -1355,6 +1355,12 @@ 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;