Also set ECF_RETURNS_TWICE for __[sig]setjmp_cancel

__setjmp_cancel and __sigsetjmp_cancel are added to glibc to implement
thread cancellation to avoid preserving shadow stack register for CET
since there is no space in thread cancellation buffer to save and
restore shadow stack register.  This works since thread cancellation
always leads to exit after longjmp.  This patch updates GCC to set
ECF_RETURNS_TWICE for __setjmp_cancel and __sigsetjmp_cancel, just like
setjmp.

gcc/

	* calls.c (special_function_p): Also set ECF_RETURNS_TWICE for
	__setjmp_cancel and __sigsetjmp_cancel.

gcc/testsuite/

	* gcc.target/i386/cet-sjlj-7.c: New test.
	* gcc.target/i386/cet-sjlj-8.c: Likewise.

gcc/calls.c

@@ -604,7 +604,7 @@ special_function_p (const_tree fndecl, int flags)
     name_decl = DECL_NAME (cgraph_node::get (fndecl)->orig_decl);
 
   if (fndecl && name_decl
-      && IDENTIFIER_LENGTH (name_decl) <= 11
+      && IDENTIFIER_LENGTH (name_decl) <= 18
       /* Exclude functions not at the file scope, or not `extern',
 	 since they are not the magic functions we would otherwise
 	 think they are.
@@ -639,6 +639,8 @@ special_function_p (const_tree fndecl, int flags)
       /* ECF_RETURNS_TWICE is safe even for -ffreestanding.  */
       if (! strcmp (tname, "setjmp")
 	  || ! strcmp (tname, "sigsetjmp")
+	  || ! strcmp (tname, "setjmp_cancel")
+	  || ! strcmp (tname, "sigsetjmp_cancel")
 	  || ! strcmp (name, "savectx")
 	  || ! strcmp (name, "vfork")
 	  || ! strcmp (name, "getcontext"))

gcc/testsuite/gcc.target/i386/cet-sjlj-7.c

@@ -0,0 +1,17 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fcf-protection -mcet" } */
+/* { dg-final { scan-assembler-times "endbr32" 2 { target ia32 } } } */
+/* { dg-final { scan-assembler-times "endbr64" 2 { target { ! ia32 } } } } */
+/* { dg-final { scan-assembler-times "call	_?__setjmp_cancel" 1 } } */
+
+extern int __setjmp_cancel (char *);
+extern char env[];
+
+int
+foo (void)
+{
+  if (__setjmp_cancel (env))
+    return 1;
+  else
+    return 0;
+}

gcc/testsuite/gcc.target/i386/cet-sjlj-8.c

@@ -0,0 +1,17 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fcf-protection -mcet" } */
+/* { dg-final { scan-assembler-times "endbr32" 2 { target ia32 } } } */
+/* { dg-final { scan-assembler-times "endbr64" 2 { target { ! ia32 } } } } */
+/* { dg-final { scan-assembler-times "call	_?__sigsetjmp_cancel" 1 } } */
+
+extern int __sigsetjmp_cancel (char *);
+extern char env[];
+
+int
+foo (void)
+{
+  if (__sigsetjmp_cancel (env))
+    return 1;
+  else
+    return 0;
+}