c-lex.c (c_lex_with_flags): For CPP_COMMENT token with PREV_FALLTHROUGH...

	* c-lex.c (c_lex_with_flags) <case CPP_COMMENT>: For CPP_COMMENT
	token with PREV_FALLTHROUGH, skip all following CPP_PADDING and
	CPP_COMMENT tokens and set add_flags to PREV_FALLTHROUGH afterwards.

	* doc/invoke.texi (-Wimplicit-fallthrough): Document the accepted
	FALLTHRU comment styles.

	* lex.c (fallthrough_comment_p): Fix off-by-one size comparison
	errors, cleanup.
	(_cpp_lex_direct): Allow arbitrary comments in between
	fallthrough_comment_p comment and following token.

	* c-c++-common/Wimplicit-fallthrough-23.c: New test.
	* c-c++-common/Wimplicit-fallthrough-24.c: New test.

From-SVN: r240884

7 files changed, 178 insertions, 7 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index a7d6689..353fdba 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2016-10-08  Jakub Jelinek  <jakub@redhat.com>
+
+	* doc/invoke.texi (-Wimplicit-fallthrough): Document the accepted
+	FALLTHRU comment styles.
+
 2016-10-07  Andrew Pinski  <apinski@cavium.com>
 
 	* config/aarch64/aarch64-arches.def (AARCH64_ARCH): #undef at the end.
diff --git a/gcc/c-family/ChangeLog b/gcc/c-family/ChangeLog
index 52ba9b8..9f6b16d 100644
--- a/gcc/c-family/ChangeLog
+++ b/gcc/c-family/ChangeLog
@@ -1,3 +1,9 @@
+2016-10-08  Jakub Jelinek  <jakub@redhat.com>
+
+	* c-lex.c (c_lex_with_flags) <case CPP_COMMENT>: For CPP_COMMENT
+	token with PREV_FALLTHROUGH, skip all following CPP_PADDING and
+	CPP_COMMENT tokens and set add_flags to PREV_FALLTHROUGH afterwards.
+
 2016-10-07  Jakub Jelinek  <jakub@redhat.com>
 
 	Implement LWG2296 helper intrinsic
diff --git a/gcc/c-family/c-lex.c b/gcc/c-family/c-lex.c
index 5c6496e..e3803b0 100644
--- a/gcc/c-family/c-lex.c
+++ b/gcc/c-family/c-lex.c
@@ -596,9 +596,21 @@ c_lex_with_flags (tree *value, location_t *loc, unsigned char *cpp_flags,
     case CPP_MACRO_ARG:
       gcc_unreachable ();
 
-    /* CPP_COMMENT will appear when compiling with -C and should be
-       ignored.  */
-     case CPP_COMMENT:
+    /* CPP_COMMENT will appear when compiling with -C.  Ignore, except
+       when it is a FALLTHROUGH comment, in that case set
+       PREV_FALLTHROUGH flag on the next non-comment token.  */
+    case CPP_COMMENT:
+      if (tok->flags & PREV_FALLTHROUGH)
+	{
+	  do
+	    {
+	      tok = cpp_get_token_with_location (parse_in, loc);
+	      type = tok->type;
+	    }
+	  while (type == CPP_PADDING || type == CPP_COMMENT);
+	  add_flags |= PREV_FALLTHROUGH;
+	  goto retry_after_at;
+	}
        goto retry;
 
     default:
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 22af6e4..e1a3e5f 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -4170,10 +4170,26 @@ C++17 provides a standard way to suppress the @option{-Wimplicit-fallthrough}
 warning using @code{[[fallthrough]];} instead of the GNU attribute.  In C++11
 or C++14 users can use @code{[[gnu::fallthrough]];}, which is a GNU extension.
 Instead of the these attributes, it is also possible to add a "falls through"
-comment to silence the warning.  GCC accepts a wide range of such comments,
-for example all of "Falls through.", "fallthru", "FALLS-THROUGH" work.  This
-comment needs to consist of two words merely, optionally followed by periods
-or whitespaces.
+comment to silence the warning.  The whole body of the C or C++ style comment
+should match one of the following regular expressions:
+
+@itemize @bullet
+
+@item @code{-fallthrough}
+
+@item @code{@@fallthrough@@}
+
+@item @code{[ \t]*FALL(S | |-)?THR(OUGH|U)\.?[ \t]*}
+
+@item @code{[ \t]*Fall((s | |-)[Tt]|t)hr(ough|u)\.?[ \t]*}
+
+@item @code{[ \t]*fall(s | |-)?thr(ough|u)\.?[ \t]*}
+
+@end itemize
+
+and the comment needs to be followed after optional whitespace and other comments
+by @code{case} or @code{default} keywords or by a user label that preceeds some
+@code{case} or @code{default} label.
 
 @smallexample
 @group
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 2214179..1868c4c 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2016-10-08  Jakub Jelinek  <jakub@redhat.com>
+
+	* c-c++-common/Wimplicit-fallthrough-23.c: New test.
+	* c-c++-common/Wimplicit-fallthrough-24.c: New test.
+
 2016-10-07  Fritz Reese  <fritzoreese@gmail.com>
 
 	* gfortran.dg/dec_union_11.f90: New testcase.
diff --git a/gcc/testsuite/c-c++-common/Wimplicit-fallthrough-23.c b/gcc/testsuite/c-c++-common/Wimplicit-fallthrough-23.c
new file mode 100644
index 0000000..137b517
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wimplicit-fallthrough-23.c
@@ -0,0 +1,123 @@
+/* { dg-do compile } */
+/* { dg-options "-Wimplicit-fallthrough" } */
+
+void bar (int);
+
+void
+foo (int i)
+{
+  switch (i)
+    {
+    case 1:
+      bar (1);			/* { dg-bogus "this statement may \[laf]* through" } */
+      /* FALLTHROUGH */
+    case 2:
+      bar (2);
+      break;
+    case 3:
+      bar (3);			/* { dg-bogus "this statement may \[laf]* through" } */
+      /* FALLS THRU.  */
+      /* Some other comment.  */
+    case 4:
+      bar (4);
+      break;
+    case 7:
+      bar (7);			/* { dg-bogus "this statement may \[laf]* through" } */
+      /* Some comment.  */
+      /* fallthrough.  */
+      /* Some other comment.  */
+      /* And yet another.  */
+    case 8:
+      bar (8);
+      break;
+    case 15:
+      bar (15);			/* { dg-bogus "this statement may \[laf]* through" } */
+      /*-fallthrough*/
+    case 16:
+      bar (16);
+      break;
+    case 17:
+      bar (17);			/* { dg-bogus "this statement may \[laf]* through" } */
+      /*@fallthrough@*/
+    case 18:
+      bar (18);
+      break;
+    case 23:
+      bar (23);			/* { dg-bogus "this statement may \[laf]* through" } */
+      /*fallthru*/
+    case 24:
+      bar (24);
+      break;
+    case 31:
+      bar (31);			/* { dg-bogus "this statement may \[laf]* through" } */
+      /*Falls thru*/
+    case 32:
+      bar (32);
+      break;
+    case 33:
+      bar (33);			/* { dg-bogus "this statement may \[laf]* through" } */
+      /*Fall-through*/
+    case 34:
+      bar (34);
+      break;
+    default:
+      break;
+    }
+  switch (i)
+    {
+    case 1:
+      bar (1);			/* { dg-bogus "this statement may \[laf]* through" } */
+      // FALLTHROUGH
+    case 2:
+      bar (2);
+      break;
+    case 3:
+      bar (3);			/* { dg-bogus "this statement may \[laf]* through" } */
+      // FALLS THRU.  
+      // Some other comment.
+    case 4:
+      bar (4);
+      break;
+    case 7:
+      bar (7);			/* { dg-bogus "this statement may \[laf]* through" } */
+      // Some comment.
+      // fallthrough
+      // Some other comment.
+      // And yet another.
+    case 8:
+      bar (8);
+      break;
+    case 15:
+      bar (15);			/* { dg-bogus "this statement may \[laf]* through" } */
+      //-fallthrough
+    case 16:
+      bar (16);
+      break;
+    case 17:
+      bar (17);			/* { dg-bogus "this statement may \[laf]* through" } */
+      //@fallthrough@
+    case 18:
+      bar (18);
+      break;
+    case 23:
+      bar (23);			/* { dg-bogus "this statement may \[laf]* through" } */
+      //fallthru
+    case 24:
+      bar (24);
+      break;
+    case 31:
+      bar (31);			/* { dg-bogus "this statement may \[laf]* through" } */
+      //Falls thru
+    case 32:
+      bar (32);
+      break;
+    case 33:
+      bar (33);			/* { dg-bogus "this statement may \[laf]* through" } */
+      //Fall-through
+    case 34:
+      bar (34);
+      break;
+    default:
+      break;
+    }
+}
diff --git a/gcc/testsuite/c-c++-common/Wimplicit-fallthrough-24.c b/gcc/testsuite/c-c++-common/Wimplicit-fallthrough-24.c
new file mode 100644
index 0000000..15f33c6
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wimplicit-fallthrough-24.c
@@ -0,0 +1,4 @@
+/* { dg-do compile } */
+/* { dg-options "-Wimplicit-fallthrough -C" } */
+
+#include "Wimplicit-fallthrough-23.c"