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improve clang support (25)


From: Bruno Haible
Subject: improve clang support (25)
Date: Wed, 12 Aug 2020 02:29:52 +0200
User-agent: KMail/5.1.3 (Linux/4.4.0-186-generic; KDE/5.18.0; x86_64; ; )

Where does clang support the 'restrict' and '__restrict' keywords? It's
like with GCC >= 3.1:

                   C mode         C++ mode

T*__restrict       supported      supported
[__restrict]       supported      error
T*restrict         supported      error
[restrict]         supported      error

According to this table, it's possible to enable restrict checking also
with clang, when it does not masquerade as GCC.


2020-08-11  Bruno Haible  <bruno@clisp.org>

        Use __restrict also on clang.
        * lib/cdefs.h (__restrict): Don't define as a macro on clang.
        (__restrict_arr): On clang, define like on GCC.
        * lib/regex.h (_Restrict_): Use '__restrict' also on clang.
        (_Restrict_arr_): Use _Restrict_ also on clang.
        * lib/spawn.in.h (_Restrict_): Use '__restrict' also on clang.
        (_Restrict_arr_): Use _Restrict_ also on clang.

diff --git a/lib/cdefs.h b/lib/cdefs.h
index 4086d51..dfa935f 100644
--- a/lib/cdefs.h
+++ b/lib/cdefs.h
@@ -399,8 +399,10 @@
 # define __extension__         /* Ignore */
 #endif
 
-/* __restrict is known in EGCS 1.2 and above. */
-#if !__GNUC_PREREQ (2,92)
+/* __restrict is known in EGCS 1.2 and above, and in clang.
+   It works also in C++ mode (outside of arrays), but only when spelled
+   as '__restrict', not 'restrict'.  */
+#if !(__GNUC_PREREQ (2,92) || __clang_major__ >= 3)
 # if defined __STDC_VERSION__ && __STDC_VERSION__ >= 199901L
 #  define __restrict   restrict
 # else
@@ -410,8 +412,9 @@
 
 /* ISO C99 also allows to declare arrays as non-overlapping.  The syntax is
      array_name[restrict]
-   GCC 3.1 supports this.  */
-#if __GNUC_PREREQ (3,1) && !defined __GNUG__
+   GCC 3.1 and clang support this.
+   This syntax is not usable in C++ mode.  */
+#if (__GNUC_PREREQ (3,1) || __clang_major__ >= 3) && !defined __cplusplus
 # define __restrict_arr        __restrict
 #else
 # ifdef __GNUC__
diff --git a/lib/regex.h b/lib/regex.h
index 5fe41c8..7418e6c 100644
--- a/lib/regex.h
+++ b/lib/regex.h
@@ -612,7 +612,9 @@ extern int re_exec (const char *);
    'configure' might #define 'restrict' to those words, so pick a
    different name.  */
 #ifndef _Restrict_
-# if defined __restrict || 2 < __GNUC__ + (95 <= __GNUC_MINOR__)
+# if defined __restrict \
+     || 2 < __GNUC__ + (95 <= __GNUC_MINOR__) \
+     || __clang_major__ >= 3
 #  define _Restrict_ __restrict
 # elif 199901L <= __STDC_VERSION__ || defined restrict
 #  define _Restrict_ restrict
@@ -620,13 +622,18 @@ extern int re_exec (const char *);
 #  define _Restrict_
 # endif
 #endif
-/* For [restrict], use glibc's __restrict_arr if available.
-   Otherwise, GCC 3.1 (not in C++ mode) and C99 support [restrict].  */
+/* For the ISO C99 syntax
+     array_name[restrict]
+   use glibc's __restrict_arr if available.
+   Otherwise, GCC 3.1 and clang support this syntax (but not in C++ mode).
+   Other ISO C99 compilers support it as well.  */
 #ifndef _Restrict_arr_
 # ifdef __restrict_arr
 #  define _Restrict_arr_ __restrict_arr
-# elif ((199901L <= __STDC_VERSION__ || 3 < __GNUC__ + (1 <= __GNUC_MINOR__)) \
-        && !defined __GNUG__)
+# elif ((199901L <= __STDC_VERSION__ \
+         || 3 < __GNUC__ + (1 <= __GNUC_MINOR__) \
+         || __clang_major__ >= 3) \
+        && !defined __cplusplus)
 #  define _Restrict_arr_ _Restrict_
 # else
 #  define _Restrict_arr_
diff --git a/lib/spawn.in.h b/lib/spawn.in.h
index c4dd01a..537fac7 100644
--- a/lib/spawn.in.h
+++ b/lib/spawn.in.h
@@ -50,7 +50,9 @@
    'configure' might #define 'restrict' to those words, so pick a
    different name.  */
 #ifndef _Restrict_
-# if defined __restrict || 2 < __GNUC__ + (95 <= __GNUC_MINOR__)
+# if defined __restrict \
+     || 2 < __GNUC__ + (95 <= __GNUC_MINOR__) \
+     || __clang_major__ >= 3
 #  define _Restrict_ __restrict
 # elif 199901L <= __STDC_VERSION__ || defined restrict
 #  define _Restrict_ restrict
@@ -58,13 +60,18 @@
 #  define _Restrict_
 # endif
 #endif
-/* For [restrict], use glibc's __restrict_arr if available.
-   Otherwise, GCC 3.1 (not in C++ mode) and C99 support [restrict].  */
+/* For the ISO C99 syntax
+     array_name[restrict]
+   use glibc's __restrict_arr if available.
+   Otherwise, GCC 3.1 and clang support this syntax (but not in C++ mode).
+   Other ISO C99 compilers support it as well.  */
 #ifndef _Restrict_arr_
 # ifdef __restrict_arr
 #  define _Restrict_arr_ __restrict_arr
-# elif ((199901L <= __STDC_VERSION__ || 3 < __GNUC__ + (1 <= __GNUC_MINOR__)) \
-        && !defined __GNUG__)
+# elif ((199901L <= __STDC_VERSION__ \
+         || 3 < __GNUC__ + (1 <= __GNUC_MINOR__) \
+         || __clang_major__ >= 3) \
+        && !defined __cplusplus)
 #  define _Restrict_arr_ _Restrict_
 # else
 #  define _Restrict_arr_




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