From: Patrick Palka <ppalka@redhat.com>
Date: Thu, 9 Jan 2025 15:50:12 +0000 (-0500)
Subject: c++: constexpr potentiality of CAST_EXPR [PR117925]
X-Git-Tag: releases/gcc-14.3.0~622
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=70cea067dd2b101edc6b3710678529eb8ba2eec2;p=thirdparty%2Fgcc.git

c++: constexpr potentiality of CAST_EXPR [PR117925]

We're incorrectly treating the templated callee (FnPtr)fnPtr, represented
as CAST_EXPR with TREE_LIST operand, as potentially constant here due to
neglecting to look through the TREE_LIST in the CAST_EXPR case of p_c_e_1.

	PR c++/117925

gcc/cp/ChangeLog:

	* constexpr.cc (potential_constant_expression_1) <case CAST_EXPR>:
	Fix check for class conversion to literal type to properly look
	through the TREE_LIST operand of a CAST_EXPR.

gcc/testsuite/ChangeLog:

	* g++.dg/template/non-dependent35.C: New test.

Reviewed-by: Jason Merrill <jason@redhat.com>
(cherry picked from commit 76d1061237b5cd57a274cd8bc8fe02a6f407baa9)
---

diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index 6025b4c29437..79dd6a7423c0 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -10279,9 +10279,14 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
 	       && (dependent_type_p (TREE_TYPE (t))
 		   || !COMPLETE_TYPE_P (TREE_TYPE (t))
 		   || literal_type_p (TREE_TYPE (t)))
-	       && TREE_OPERAND (t, 0))
-	{
-	  tree type = TREE_TYPE (TREE_OPERAND (t, 0));
+	       && TREE_OPERAND (t, 0)
+	       && (TREE_CODE (t) != CAST_EXPR
+		   || !TREE_CHAIN (TREE_OPERAND (t, 0))))
+	{
+	  tree from = TREE_OPERAND (t, 0);
+	  if (TREE_CODE (t) == CAST_EXPR)
+	    from = TREE_VALUE (from);
+	  tree type = TREE_TYPE (from);
 	  /* If this is a dependent type, it could end up being a class
 	     with conversions.  */
 	  if (type == NULL_TREE || WILDCARD_TYPE_P (type))
diff --git a/gcc/testsuite/g++.dg/template/non-dependent35.C b/gcc/testsuite/g++.dg/template/non-dependent35.C
new file mode 100644
index 000000000000..7e3ba99b0235
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/non-dependent35.C
@@ -0,0 +1,8 @@
+// PR c++/117925
+
+typedef int(*FnPtr)();
+
+template<class T>
+void fnICE(void* fnPtr) {
+  ((FnPtr)fnPtr)();
+}