From 5094c4400a8687dcf44f5993aee3a88e98519f3b Mon Sep 17 00:00:00 2001
From: Jason Merrill <jason@redhat.com>
Date: Thu, 4 Jun 2020 15:56:57 -0400
Subject: [PATCH] c++: Fix pretty-print of pointer minus integer.

For whatever reason, GCC internally represents a pointer minus an integer as
a pointer plus a very large unsigned integer.  But exposing that to users is
unsightly, and it's easy enough to show the real value.

gcc/cp/ChangeLog:

	* error.c (dump_binary_op): Handle negative operand to
	POINTER_PLUS_EXPR.

gcc/c-family/ChangeLog:

	* c-pretty-print.c (pp_c_additive_expression): Handle negative
	operand to POINTER_PLUS_EXPR.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/constexpr-ptrsub2.C: New test.
---
 gcc/c-family/c-pretty-print.c                  | 11 ++++++++++-
 gcc/cp/error.c                                 |  9 ++++++++-
 gcc/testsuite/g++.dg/cpp0x/constexpr-ptrsub2.C |  4 ++++
 3 files changed, 22 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-ptrsub2.C

diff --git a/gcc/c-family/c-pretty-print.c b/gcc/c-family/c-pretty-print.c
index 32f30f2d452..71baf5e2ede 100644
--- a/gcc/c-family/c-pretty-print.c
+++ b/gcc/c-family/c-pretty-print.c
@@ -1898,7 +1898,16 @@ pp_c_additive_expression (c_pretty_printer *pp, tree e)
       else
 	pp_minus (pp);
       pp_c_whitespace (pp);
-      pp->multiplicative_expression (TREE_OPERAND (e, 1));
+      {
+	tree op1 = TREE_OPERAND (e, 1);
+	if (code == POINTER_PLUS_EXPR
+	    && TREE_CODE (op1) == INTEGER_CST
+	    && tree_int_cst_sign_bit (op1))
+	  /* A pointer minus an integer is represented internally as plus a very
+	     large number, don't expose that to users.  */
+	  op1 = convert (ssizetype, op1);
+	pp->multiplicative_expression (op1);
+      }
       break;
 
     default:
diff --git a/gcc/cp/error.c b/gcc/cp/error.c
index 46970f9b699..0d6375e5e14 100644
--- a/gcc/cp/error.c
+++ b/gcc/cp/error.c
@@ -2909,7 +2909,14 @@ dump_binary_op (cxx_pretty_printer *pp, const char *opstring, tree t,
   else
     pp_string (pp, M_("<unknown operator>"));
   pp_cxx_whitespace (pp);
-  dump_expr (pp, TREE_OPERAND (t, 1), flags | TFF_EXPR_IN_PARENS);
+  tree op1 = TREE_OPERAND (t, 1);
+  if (TREE_CODE (t) == POINTER_PLUS_EXPR
+      && TREE_CODE (op1) == INTEGER_CST
+      && tree_int_cst_sign_bit (op1))
+    /* A pointer minus an integer is represented internally as plus a very
+       large number, don't expose that to users.  */
+    op1 = convert (ssizetype, op1);
+  dump_expr (pp, op1, flags | TFF_EXPR_IN_PARENS);
   pp_cxx_right_paren (pp);
 }
 
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-ptrsub2.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-ptrsub2.C
new file mode 100644
index 00000000000..fd644ad7854
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-ptrsub2.C
@@ -0,0 +1,4 @@
+// { dg-do compile { target c++11 } }
+
+char c;
+constexpr char p2 = *(&c - 1);	// { dg-error "-1" }
-- 
2.30.2