c: Default to -std=gnu23

Change the default language version for C compilation from -std=gnu17
to -std=gnu23.  A few tests are updated to remove local definitions of
bool, true and false (where making such an unconditional test change
seemed to make more sense than changing the test conditionally earlier
or building it with -std=gnu17); most test issues were already
addressed in previous patches.  In the case of
ctf-function-pointers-2.c, it was agreed in bug 117289 that it would
be OK to put -std=gnu17 in the test and leave more optimal BTF / CTF
output for this test as a potential future improvement.

Since the original test fixes, more such fixes have become necessary
and so are included in this patch.  More noinline attributes are added
to simulate-thread tests where () meaning a prototype affected test
results, while gcc.dg/torture/pr117496-1.c (a test declaring a
function with () then calling it with arguments) gets -std=gnu17
added.

Bootstrapped with no regressions for x86_64-pc-linux-gnu.

NOTE: it's likely there are target-specific tests for non-x86 targets
that need updating as a result of this change.  See commit
9fb5348e30 ("testsuite: Prepare for
-std=gnu23 default") for examples of changes to prepare the testsuite
to work with a -std=gnu23 default.  In most cases, adding
-Wno-old-style-definition (for warnings for old-style function
definitions) or -std=gnu17 (for other issues such as unprototyped
function declarations with ()) is appropriate, but watch out for cases
that indicate bugs with -std=gnu23 (in particular, any ICEs - there
was only the one nested function test where I had to fix an ICE on
x86_64).

gcc/
	* doc/invoke.texi (-std=gnu17, -std=gnu23): Document -std=gnu23 as
	default for C code.

gcc/c-family/
	* c-opts.cc (c_common_init_options): Default to C23.

gcc/testsuite/
	* c-c++-common/analyzer/asm-x86-dyndbg-2.c,
	c-c++-common/analyzer/asm-x86-lp64-2.c,
	c-c++-common/analyzer/attr-malloc-CVE-2019-19078-usb-leak.c,
	c-c++-common/analyzer/coreutils-cksum-pr108664.c,
	c-c++-common/analyzer/feasibility-3.c,
	c-c++-common/analyzer/pr105783.c, c-c++-common/analyzer/sock-1.c,
	c-c++-common/attributes-4.c, gcc.dg/Warray-bounds-78.c,
	gcc.dg/analyzer/asm-x86-dyndbg-1.c: Do not define bool, true or
	false.
	* gcc.dg/debug/ctf/ctf-function-pointers-2.c: Use -std-gnu17.
	* gcc.dg/gnu23-version-2.c: New test.
	* gcc.dg/simulate-thread/atomic-load-int.c,
	gcc.dg/simulate-thread/atomic-load-longlong.c,
	gcc.dg/simulate-thread/atomic-load-short.c: Add more noinline
	attributes.
	* gcc.dg/torture/pr117496-1.c: Use -std=gnu17.

gcc/c-family/c-opts.cc

@@ -261,8 +261,8 @@ c_common_init_options (unsigned int decoded_options_count,
 
   if (c_language == clk_c)
     {
-      /* The default for C is gnu17.  */
-      set_std_c17 (false /* ISO */);
+      /* The default for C is gnu23.  */
+      set_std_c23 (false /* ISO */);
 
       /* If preprocessing assembly language, accept any of the C-family
 	 front end options since the driver may pass them through.  */

gcc/doc/invoke.texi

@@ -2501,11 +2501,12 @@ The name @samp{gnu1x} is deprecated.
 
 @item gnu17
 @itemx gnu18
-GNU dialect of ISO C17.  This is the default for C code.
+GNU dialect of ISO C17.
 
 @item gnu23
 @itemx gnu2x
-GNU dialect of ISO C23.  The name @samp{gnu2x} is deprecated.
+GNU dialect of ISO C23.  This is the default for C code.  The name
+@samp{gnu2x} is deprecated.
 
 @item gnu2y
 The next version of the ISO C standard, still under development, plus

gcc/testsuite/c-c++-common/analyzer/asm-x86-dyndbg-2.c

@@ -8,12 +8,6 @@
 /* Adapted from various files in the Linux kernel, all of which have:  */
 /* SPDX-License-Identifier: GPL-2.0 */
 
-#ifndef __cplusplus 
-  typedef _Bool bool;
-  #define true 1
-  #define false 0
-#endif
-
 typedef struct {} atomic_t;
 
 /* Adapted from include/linux/compiler_attributes.h  */

gcc/testsuite/c-c++-common/analyzer/asm-x86-lp64-2.c

@@ -3,10 +3,6 @@
 
 /* Adapted from Linux x86: page_ref_dec_and_test.c (GPL-2.0).  */
 
-#ifndef __cplusplus 
-  typedef _Bool bool;
-#endif
-
 typedef struct {
   int counter;
 } atomic_t;

gcc/testsuite/c-c++-common/analyzer/attr-malloc-CVE-2019-19078-usb-leak.c

@@ -4,10 +4,6 @@
 typedef unsigned char u8;
 typedef unsigned short u16;
 
-#ifndef __cplusplus 
-  typedef _Bool bool;
-#endif
-
 #define	ENOMEM		12
 #define	EINVAL		22
 

gcc/testsuite/c-c++-common/analyzer/coreutils-cksum-pr108664.c

@@ -8,10 +8,6 @@ typedef unsigned int __uint32_t;
 typedef unsigned long int __uintmax_t;
 typedef struct _IO_FILE FILE;
 
-#ifndef __cplusplus
-  typedef _Bool bool;
-#endif
-
 extern size_t
 fread_unlocked(void* __restrict __ptr,
                size_t __size,

gcc/testsuite/c-c++-common/analyzer/feasibility-3.c

@@ -6,9 +6,6 @@
 /* Types.  */
 
 typedef unsigned char u8;
-#ifndef __cplusplus
-typedef _Bool bool;
-#endif
 typedef unsigned int gfp_t;
 
 struct file;

gcc/testsuite/c-c++-common/analyzer/pr105783.c

@@ -1,9 +1,5 @@
 /* { dg-additional-options "-O" } */
 
-#ifndef __cplusplus
-typedef _Bool bool;
-#endif
-
 struct ss_s {
     union out_or_counting_u {
     	char *newstr;

gcc/testsuite/c-c++-common/analyzer/sock-1.c

@@ -5,9 +5,6 @@ typedef __u32 u32;
 typedef __s64 s64;
 typedef __u64 u64;
 typedef long long __kernel_time64_t;
-#ifndef __cplusplus
-typedef _Bool bool;
-#endif
 typedef __s64 time64_t;
 struct __kernel_timespec {
  __kernel_time64_t tv_sec;

gcc/testsuite/c-c++-common/attributes-4.c

@@ -11,7 +11,6 @@
 typedef __CHAR16_TYPE__ char16_t;
 typedef __CHAR32_TYPE__ char32_t;
 #elif !__cplusplus
-typedef _Bool           bool;
 typedef __CHAR16_TYPE__ char16_t;
 typedef __CHAR32_TYPE__ char32_t;
 typedef __WCHAR_TYPE__  wchar_t;

gcc/testsuite/gcc.dg/Warray-bounds-78.c

@@ -3,8 +3,6 @@
    { dg-do compile }
    { dg-options "-O2 -Wall -Wno-strict-aliasing" } */
 
-typedef _Bool bool;
-
 #define NOIPA __attribute__ ((noipa))
 
 struct S { };

gcc/testsuite/gcc.dg/analyzer/asm-x86-dyndbg-1.c

@@ -8,10 +8,6 @@
 /* Adapted from various files in the Linux kernel, all of which have:  */
 /* SPDX-License-Identifier: GPL-2.0 */
 
-typedef _Bool			bool;
-#define true 1
-#define false 0
-
 typedef struct {
 	int counter;
 } atomic_t;

gcc/testsuite/gcc.dg/debug/ctf/ctf-function-pointers-2.c

@@ -4,7 +4,7 @@
    different function pointer types.  */
 
 /* { dg-do compile } */
-/* { dg-options "-O0 -gctf -dA" } */
+/* { dg-options "-O0 -gctf -dA -std=gnu17" } */
 /* { dg-final { scan-assembler-times "\[\t \]0x16000001\[\t \]+\[^\n\]*ctt_info" 1 } } */
 /* { dg-final { scan-assembler-times "ascii \"rcu_callback_t.0\"\[\t \]+\[^\n\]*ctf_string" 1 } } */
 /* { dg-final { scan-assembler-times "ascii \"func.0\"\[\t \]+\[^\n\]*ctf_string" 1 } } */

gcc/testsuite/gcc.dg/gnu23-version-2.c

@@ -0,0 +1,11 @@
+/* Test __STDC_VERSION__ for C23 with GNU extensions.  Test that -std=gnu23 is
+   the default (replace this test when updating the default to a later version
+   than gnu23).  */
+/* { dg-do compile } */
+/* { dg-options "" } */
+
+#if __STDC_VERSION__ == 202311L
+int i;
+#else
+#error "Bad __STDC_VERSION__."
+#endif

gcc/testsuite/gcc.dg/simulate-thread/atomic-load-int.c

@@ -49,6 +49,7 @@ unsigned int table[16] = {
 int table_cycle_size = 16;
 
 /* Return 0 if 'result' is a valid value to have loaded.  */
+__attribute__((noinline))
 int verify_result ()
 {
   int x;
@@ -69,6 +70,7 @@ int verify_result ()
 }
 
 /* Iterate VALUE through the different valid values. */
+__attribute__((noinline))
 void simulate_thread_other_threads ()
 {
   static int current = 0;
@@ -78,11 +80,13 @@ void simulate_thread_other_threads ()
   value = table[current];
 }
 
+__attribute__((noinline))
 int simulate_thread_step_verify ()
 {
   return verify_result ();
 }
 
+__attribute__((noinline))
 int simulate_thread_final_verify ()
 {
   return verify_result ();

gcc/testsuite/gcc.dg/simulate-thread/atomic-load-longlong.c

@@ -51,6 +51,7 @@ unsigned long long table[16] = {
 int table_cycle_size = 16;
 
 /* Return 0 if 'result' is a valid value to have loaded.  */
+__attribute__((noinline))
 int verify_result ()
 {
   int x;
@@ -71,6 +72,7 @@ int verify_result ()
 }
 
 /* Iterate VALUE through the different valid values. */
+__attribute__((noinline))
 void simulate_thread_other_threads ()
 {
   static int current = 0;
@@ -80,11 +82,13 @@ void simulate_thread_other_threads ()
   value = table[current];
 }
 
+__attribute__((noinline))
 int simulate_thread_step_verify ()
 {
   return verify_result ();
 }
 
+__attribute__((noinline))
 int simulate_thread_final_verify ()
 {
   return verify_result ();

gcc/testsuite/gcc.dg/simulate-thread/atomic-load-short.c

@@ -49,6 +49,7 @@ unsigned short table[16] = {
 int table_cycle_size = 16;
 
 /* Return 0 if 'result' is a valid value to have loaded.  */
+__attribute__((noinline))
 int verify_result ()
 {
   int x;
@@ -69,6 +70,7 @@ int verify_result ()
 }
 
 /* Iterate VALUE through the different valid values. */
+__attribute__((noinline))
 void simulate_thread_other_threads ()
 {
   static int current = 0;
@@ -78,11 +80,13 @@ void simulate_thread_other_threads ()
   value = table[current];
 }
 
+__attribute__((noinline))
 int simulate_thread_step_verify ()
 {
   return verify_result ();
 }
 
+__attribute__((noinline))
 int simulate_thread_final_verify ()
 {
   return verify_result ();

gcc/testsuite/gcc.dg/torture/pr117496-1.c

@@ -1,4 +1,5 @@
 /* { dg-do compile } */
+/* { dg-additional-options "-std=gnu17" } */
 
 
 /* PR tree-optimization/117496 */