diff --git a/gcc/c-family/c-opts.cc b/gcc/c-family/c-opts.cc
index 127f9553e0c..3f2cabf9448 100644
--- a/gcc/c-family/c-opts.cc
+++ b/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.  */
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 36d79d1c76b..929feaf23fb 100644
--- a/gcc/doc/invoke.texi
+++ b/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
diff --git a/gcc/testsuite/c-c++-common/analyzer/asm-x86-dyndbg-2.c b/gcc/testsuite/c-c++-common/analyzer/asm-x86-dyndbg-2.c
index d5e748c9acd..db77ce9a4f9 100644
--- a/gcc/testsuite/c-c++-common/analyzer/asm-x86-dyndbg-2.c
+++ b/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  */
diff --git a/gcc/testsuite/c-c++-common/analyzer/asm-x86-lp64-2.c b/gcc/testsuite/c-c++-common/analyzer/asm-x86-lp64-2.c
index 37c487a69c2..5d32c9a66c3 100644
--- a/gcc/testsuite/c-c++-common/analyzer/asm-x86-lp64-2.c
+++ b/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;
diff --git a/gcc/testsuite/c-c++-common/analyzer/attr-malloc-CVE-2019-19078-usb-leak.c b/gcc/testsuite/c-c++-common/analyzer/attr-malloc-CVE-2019-19078-usb-leak.c
index 24fb46bd5a9..87ad42a3c32 100644
--- a/gcc/testsuite/c-c++-common/analyzer/attr-malloc-CVE-2019-19078-usb-leak.c
+++ b/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
 
diff --git a/gcc/testsuite/c-c++-common/analyzer/coreutils-cksum-pr108664.c b/gcc/testsuite/c-c++-common/analyzer/coreutils-cksum-pr108664.c
index 7ae4e6b06be..67dcbce09d0 100644
--- a/gcc/testsuite/c-c++-common/analyzer/coreutils-cksum-pr108664.c
+++ b/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,
diff --git a/gcc/testsuite/c-c++-common/analyzer/feasibility-3.c b/gcc/testsuite/c-c++-common/analyzer/feasibility-3.c
index 06194f85069..06aed88b5e8 100644
--- a/gcc/testsuite/c-c++-common/analyzer/feasibility-3.c
+++ b/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;
diff --git a/gcc/testsuite/c-c++-common/analyzer/pr105783.c b/gcc/testsuite/c-c++-common/analyzer/pr105783.c
index f17519415ce..34d21c62aef 100644
--- a/gcc/testsuite/c-c++-common/analyzer/pr105783.c
+++ b/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;
diff --git a/gcc/testsuite/c-c++-common/analyzer/sock-1.c b/gcc/testsuite/c-c++-common/analyzer/sock-1.c
index e5e2f23bba0..57938c0c0ab 100644
--- a/gcc/testsuite/c-c++-common/analyzer/sock-1.c
+++ b/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;
diff --git a/gcc/testsuite/c-c++-common/attributes-4.c b/gcc/testsuite/c-c++-common/attributes-4.c
index 55661eb792c..d78cdae2e11 100644
--- a/gcc/testsuite/c-c++-common/attributes-4.c
+++ b/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;
diff --git a/gcc/testsuite/gcc.dg/Warray-bounds-78.c b/gcc/testsuite/gcc.dg/Warray-bounds-78.c
index 73c335fd8a6..26b8a9bf9fe 100644
--- a/gcc/testsuite/gcc.dg/Warray-bounds-78.c
+++ b/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 { };
diff --git a/gcc/testsuite/gcc.dg/analyzer/asm-x86-dyndbg-1.c b/gcc/testsuite/gcc.dg/analyzer/asm-x86-dyndbg-1.c
index cce3f6b80bc..9ea86206fd8 100644
--- a/gcc/testsuite/gcc.dg/analyzer/asm-x86-dyndbg-1.c
+++ b/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;
diff --git a/gcc/testsuite/gcc.dg/debug/ctf/ctf-function-pointers-2.c b/gcc/testsuite/gcc.dg/debug/ctf/ctf-function-pointers-2.c
index 80b9c188cee..55c73873a84 100644
--- a/gcc/testsuite/gcc.dg/debug/ctf/ctf-function-pointers-2.c
+++ b/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 } } */
diff --git a/gcc/testsuite/gcc.dg/gnu23-version-2.c b/gcc/testsuite/gcc.dg/gnu23-version-2.c
new file mode 100644
index 00000000000..008f445ecdf
--- /dev/null
+++ b/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
diff --git a/gcc/testsuite/gcc.dg/simulate-thread/atomic-load-int.c b/gcc/testsuite/gcc.dg/simulate-thread/atomic-load-int.c
index a40c3ddcb31..9f75cedd023 100644
--- a/gcc/testsuite/gcc.dg/simulate-thread/atomic-load-int.c
+++ b/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 ();
diff --git a/gcc/testsuite/gcc.dg/simulate-thread/atomic-load-longlong.c b/gcc/testsuite/gcc.dg/simulate-thread/atomic-load-longlong.c
index 524b9845b91..6c3b3a3981f 100644
--- a/gcc/testsuite/gcc.dg/simulate-thread/atomic-load-longlong.c
+++ b/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 ();
diff --git a/gcc/testsuite/gcc.dg/simulate-thread/atomic-load-short.c b/gcc/testsuite/gcc.dg/simulate-thread/atomic-load-short.c
index 62690cea5f8..53b8c084eb3 100644
--- a/gcc/testsuite/gcc.dg/simulate-thread/atomic-load-short.c
+++ b/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 ();
diff --git a/gcc/testsuite/gcc.dg/torture/pr117496-1.c b/gcc/testsuite/gcc.dg/torture/pr117496-1.c
index f35d13dfa85..d68286ef772 100644
--- a/gcc/testsuite/gcc.dg/torture/pr117496-1.c
+++ b/gcc/testsuite/gcc.dg/torture/pr117496-1.c
@@ -1,4 +1,5 @@
 /* { dg-do compile } */
+/* { dg-additional-options "-std=gnu17" } */
 
 
 /* PR tree-optimization/117496 */