From: Marek Polacek <polacek@redhat.com>
Date: Tue, 17 Sep 2024 18:34:30 +0000 (-0400)
Subject: c++: fix constexpr cast from void* diag issue [PR116741]
X-Git-Tag: basepoints/gcc-16~5879
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=d6d8445c85509b66a59aa6247ad7b2cfeab17725;p=thirdparty%2Fgcc.git

c++: fix constexpr cast from void* diag issue [PR116741]

The result of build_fold_indirect_ref can be a COMPONENT_REF in
which case using DECL_SOURCE_LOCATION will crash.  Look at its op1
instead.

	PR c++/116741

gcc/cp/ChangeLog:

	* constexpr.cc (cxx_eval_constant_expression) <case CONVERT_EXPR>: If
	the result of build_fold_indirect_ref is a COMPONENT_REF, use its op1.
	Check DECL_P before calling inform.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp26/constexpr-voidptr4.C: New test.

Reviewed-by: Jason Merrill <jason@redhat.com>
---

diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index c3668b0d7d3..f6fd059be46 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -8201,8 +8201,11 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx, tree t,
 			      TREE_TYPE (op), TREE_TYPE (TREE_TYPE (sop)),
 			      TREE_TYPE (type));
 		    tree obj = build_fold_indirect_ref (sop);
-		    inform (DECL_SOURCE_LOCATION (obj),
-			    "pointed-to object declared here");
+		    if (TREE_CODE (obj) == COMPONENT_REF)
+		      obj = TREE_OPERAND (obj, 1);
+		    if (DECL_P (obj))
+		      inform (DECL_SOURCE_LOCATION (obj),
+			      "pointed-to object declared here");
 		  }
 		*non_constant_p = true;
 		return t;
diff --git a/gcc/testsuite/g++.dg/cpp26/constexpr-voidptr4.C b/gcc/testsuite/g++.dg/cpp26/constexpr-voidptr4.C
new file mode 100644
index 00000000000..53563c928f2
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp26/constexpr-voidptr4.C
@@ -0,0 +1,29 @@
+// PR c++/116741
+// { dg-do compile { target c++26 } }
+
+struct S {
+  int foo;    // { dg-message "pointed-to object" }
+};
+
+struct S2 {
+  int foo;    // { dg-message "pointed-to object" }
+};
+
+struct X {
+  S2 s;
+};
+
+constexpr float f1() {
+  S s;
+  void* p = &s.foo;
+  return *static_cast<float*>(p); // { dg-error "not allowed in a constant expression" }
+}
+
+constexpr float f2() {
+  X x;
+  void* p = &x.s.foo;
+  return *static_cast<float*>(p); // { dg-error "not allowed in a constant expression" }
+}
+
+constexpr auto x1 = f1();
+constexpr auto x2 = f2();