10.1.0: backport PR95508, ICE on array subscript implicit conversion

Reported-by: hsk17@mail.de
Bug: https://bugs.gentoo.org/729434
Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>

2 files changed, 107 insertions, 0 deletions

diff --git a/10.1.0/gentoo/35_all_ICE-array-subscript-PR95508.patch b/10.1.0/gentoo/35_all_ICE-array-subscript-PR95508.patch
new file mode 100644
index 0000000..37abd53
--- /dev/null
+++ b/10.1.0/gentoo/35_all_ICE-array-subscript-PR95508.patch
@@ -0,0 +1,106 @@
+https://gcc.gnu.org/PR95508
+https://bugs.gentoo.org/729434
+
+From 1bab254fd30c2b94a675b9057349fc80946375b1 Mon Sep 17 00:00:00 2001
+From: Marek Polacek <polacek@redhat.com>
+Date: Wed, 17 Jun 2020 14:38:05 -0400
+Subject: [PATCH] c++: ICE with IMPLICIT_CONV_EXPR in array subscript [PR95508]
+
+Since r10-7096 convert_like, when called in a template, creates an
+IMPLICIT_CONV_EXPR when we're converting to/from array type.
+
+In this test, we have e[f], and we're converting f (of type class A) to
+int, so convert_like in build_new_op_1 created the IMPLICIT_CONV_EXPR
+that got into cp_build_array_ref which calls maybe_constant_value.  My
+patch above failed to adjust this spot to call fold_non_dependent_expr
+instead, which can handle codes like I_C_E in a template.  Fixed by
+using a new function maybe_fold_non_dependent_expr, which, if the expr
+can't be evaluated to a constant, returns the original expression.
+
+gcc/cp/ChangeLog:
+
+	PR c++/95508
+	* constexpr.c (maybe_fold_non_dependent_expr): New.
+	* cp-tree.h (maybe_fold_non_dependent_expr): Declare.
+	* typeck.c (cp_build_array_ref): Call maybe_fold_non_dependent_expr
+	instead of maybe_constant_value.
+
+gcc/testsuite/ChangeLog:
+
+	PR c++/95508
+	* g++.dg/template/conv16.C: New test.
+---
+ gcc/cp/constexpr.c                     | 13 +++++++++++++
+ gcc/cp/cp-tree.h                       |  2 ++
+ gcc/cp/typeck.c                        |  2 +-
+ gcc/testsuite/g++.dg/template/conv16.C | 17 +++++++++++++++++
+ 4 files changed, 33 insertions(+), 1 deletion(-)
+ create mode 100644 gcc/testsuite/g++.dg/template/conv16.C
+
+--- a/gcc/cp/constexpr.c
++++ b/gcc/cp/constexpr.c
+@@ -7043,6 +7043,19 @@ fold_non_dependent_expr (tree t,
+   return maybe_constant_value (t, object, manifestly_const_eval);
+ }
+ 
++/* Like fold_non_dependent_expr, but if EXPR couldn't be folded to a constant,
++   return the original expression.  */
++
++tree
++maybe_fold_non_dependent_expr (tree expr,
++			       tsubst_flags_t complain/*=tf_warning_or_error*/)
++{
++  tree t = fold_non_dependent_expr (expr, complain);
++  if (t && TREE_CONSTANT (t))
++    return t;
++
++  return expr;
++}
+ 
+ /* Like maybe_constant_init but first fully instantiate the argument.  */
+ 
+--- a/gcc/cp/cp-tree.h
++++ b/gcc/cp/cp-tree.h
+@@ -7955,6 +7955,8 @@ extern tree maybe_constant_init			(tree, tree = NULL_TREE, bool = false);
+ extern tree fold_non_dependent_expr		(tree,
+ 						 tsubst_flags_t = tf_warning_or_error,
+ 						 bool = false, tree = NULL_TREE);
++extern tree maybe_fold_non_dependent_expr	(tree,
++						 tsubst_flags_t = tf_warning_or_error);
+ extern tree fold_non_dependent_init		(tree,
+ 						 tsubst_flags_t = tf_warning_or_error,
+ 						 bool = false);
+--- a/gcc/cp/typeck.c
++++ b/gcc/cp/typeck.c
+@@ -3553,7 +3553,7 @@ cp_build_array_ref (location_t loc, tree array, tree idx,
+ 	 pointer arithmetic.)  */
+       idx = cp_perform_integral_promotions (idx, complain);
+ 
+-      idx = maybe_constant_value (idx);
++      idx = maybe_fold_non_dependent_expr (idx, complain);
+ 
+       /* An array that is indexed by a non-constant
+ 	 cannot be stored in a register; we must be able to do
+--- /dev/null
++++ b/gcc/testsuite/g++.dg/template/conv16.C
+@@ -0,0 +1,17 @@
++// PR c++/95508
++// { dg-do compile }
++
++template <typename>
++struct A;
++template <typename>
++struct B {
++  operator int () { return 0; }
++};
++template <>
++struct A<unsigned> : B<int> {};
++struct D {
++  template <typename>
++  int foo () { return e[f]; }
++  int e[6];
++  A<unsigned> f;
++};
+-- 
+2.27.0
+
diff --git a/10.1.0/gentoo/README.history b/10.1.0/gentoo/README.history
index 480a54e..72e0086 100644
--- a/10.1.0/gentoo/README.history
+++ b/10.1.0/gentoo/README.history
@@ -1,6 +1,7 @@
 3		TODO
 	33_all_avx512-scalar-PR95528.patch
 	34_all_cet-cross-x86.patch
+	35_all_ICE-array-subscript-PR95508.patch
 
 2		11 June 2020
 	+ 29_all_fix-float-hang-PR95118.patch