From 0b974dba2d6b5581ce422ed883209de46f313fb6 Mon Sep 17 00:00:00 2001
From: Andres Freund <andres@anarazel.de>
Date: Wed, 11 Oct 2017 16:01:52 -0700
Subject: [PATCH] Add configure infrastructure to detect support for C99's
 restrict.

Will be used in later commits improving performance for a few key
routines where information about aliasing allows for significantly
better code generation.

This allows to use the C99 'restrict' keyword without breaking C89, or
for that matter C++, compilers. If not supported it's defined to be
empty.

Author: Andres Freund
Discussion: https://postgr.es/m/20170914063418.sckdzgjfrsbekae4@alap3.anarazel.de
---
 configure                     | 46 +++++++++++++++++++++++++++++++++++
 configure.in                  |  1 +
 src/include/pg_config.h.in    | 14 +++++++++++
 src/include/pg_config.h.win32 | 11 +++++++++
 4 files changed, 72 insertions(+)

diff --git a/configure b/configure
index 98cb8b28814..910f0fc3736 100755
--- a/configure
+++ b/configure
@@ -11545,6 +11545,52 @@ _ACEOF
     ;;
 esac
 
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for C/C++ restrict keyword" >&5
+$as_echo_n "checking for C/C++ restrict keyword... " >&6; }
+if ${ac_cv_c_restrict+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  ac_cv_c_restrict=no
+   # The order here caters to the fact that C++ does not require restrict.
+   for ac_kw in __restrict __restrict__ _Restrict restrict; do
+     cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+typedef int * int_ptr;
+	int foo (int_ptr $ac_kw ip) {
+	return ip[0];
+       }
+int
+main ()
+{
+int s[1];
+	int * $ac_kw t = s;
+	t[0] = 0;
+	return foo(t)
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+  ac_cv_c_restrict=$ac_kw
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+     test "$ac_cv_c_restrict" != no && break
+   done
+
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_cv_c_restrict" >&5
+$as_echo "$ac_cv_c_restrict" >&6; }
+
+ case $ac_cv_c_restrict in
+   restrict) ;;
+   no) $as_echo "#define restrict /**/" >>confdefs.h
+ ;;
+   *)  cat >>confdefs.h <<_ACEOF
+#define restrict $ac_cv_c_restrict
+_ACEOF
+ ;;
+ esac
+
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for printf format archetype" >&5
 $as_echo_n "checking for printf format archetype... " >&6; }
 if ${pgac_cv_printf_archetype+:} false; then :
diff --git a/configure.in b/configure.in
index 4548db0dd3c..ab990d69f4c 100644
--- a/configure.in
+++ b/configure.in
@@ -1299,6 +1299,7 @@ fi
 m4_defun([AC_PROG_CC_STDC], []) dnl We don't want that.
 AC_C_BIGENDIAN
 AC_C_INLINE
+AC_C_RESTRICT
 PGAC_PRINTF_ARCHETYPE
 AC_C_FLEXIBLE_ARRAY_MEMBER
 PGAC_C_SIGNED
diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in
index b0298cca19c..80ee37dd622 100644
--- a/src/include/pg_config.h.in
+++ b/src/include/pg_config.h.in
@@ -923,6 +923,20 @@
    if such a type exists, and if the system does not define it. */
 #undef intptr_t
 
+/* Define to the equivalent of the C99 'restrict' keyword, or to
+   nothing if this is not supported.  Do not define if restrict is
+   supported directly.  */
+#undef restrict
+/* Work around a bug in Sun C++: it does not support _Restrict or
+   __restrict__, even though the corresponding Sun C compiler ends up with
+   "#define restrict _Restrict" or "#define restrict __restrict__" in the
+   previous line.  Perhaps some future version of Sun C++ will work with
+   restrict; if so, hopefully it defines __RESTRICT like Sun C does.  */
+#if defined __SUNPRO_CC && !defined __RESTRICT
+# define _Restrict
+# define __restrict__
+#endif
+
 /* Define to empty if the C compiler does not understand signed types. */
 #undef signed
 
diff --git a/src/include/pg_config.h.win32 b/src/include/pg_config.h.win32
index b76aad02676..3be1c235aaa 100644
--- a/src/include/pg_config.h.win32
+++ b/src/include/pg_config.h.win32
@@ -681,6 +681,17 @@
 #define inline __inline
 #endif
 
+/* Define to the equivalent of the C99 'restrict' keyword, or to
+   nothing if this is not supported.  Do not define if restrict is
+   supported directly.  */
+/* Visual Studio 2008 and upwards */
+#if (_MSC_VER >= 1500)
+/* works for C and C++ in msvc */
+#define restrict __restrict
+#else
+#define restrict
+#endif
+
 /* Define to empty if the C compiler does not understand signed types. */
 /* #undef signed */