re PR c/49859 (gcc could warn about statements between "switch" and first "case")

	PR c/49859
	* common.opt (Wswitch-unreachable): New option.
	* doc/invoke.texi: Document -Wswitch-unreachable.
	* gimplify.c (gimplify_switch_expr): Implement the -Wswitch-unreachable
	warning.

	* c-c++-common/Wswitch-unreachable-1.c: New test.
	* gcc.dg/Wswitch-unreachable-1.c: New test.
	* c-c++-common/goacc/sb-2.c (void foo): Add dg-warning.
	* g++.dg/cpp0x/lambda/lambda-switch.C (main): Likewise.
	* g++.dg/gomp/block-10.C: Likewise.
	* gcc.dg/gomp/block-10.c: Likewise.
	* g++.dg/gomp/block-9.C: Likewise.
	* gcc.dg/gomp/block-9.c: Likewise.
	* g++.dg/gomp/target-1.C: Likewise.
	* g++.dg/gomp/target-2.C: Likewise.
	* gcc.dg/gomp/target-1.c: Likewise.
	* gcc.dg/gomp/target-2.c: Likewise. 
	* g++.dg/gomp/taskgroup-1.C: Likewise.
	* gcc.dg/gomp/taskgroup-1.c: Likewise.
	* gcc.dg/gomp/teams-1.c: Likewise.
	* g++.dg/gomp/teams-1.C: Likewise.
	* g++.dg/overload/error3.C: Likewise.
	* g++.dg/tm/jump1.C: Likewise.
	* g++.dg/torture/pr40335.C: Likewise.
	* gcc.dg/c99-vla-jump-5.c: Likewise.
	* gcc.dg/switch-warn-1.c: Likewise.
	* gcc.dg/Wjump-misses-init-1.c: Use -Wno-switch-unreachable.
	* gcc.dg/nested-func-1.c: Likewise.
	* gcc.dg/pr67784-4.c: Likewise.

From-SVN: r236597

gcc/ChangeLog

-2016-05-23 Bin Cheng  <bin.cheng@arm.com>
+2016-05-23  Marek Polacek  <polacek@redhat.com>
+
+	PR c/49859
+	* common.opt (Wswitch-unreachable): New option.
+	* doc/invoke.texi: Document -Wswitch-unreachable.
+	* gimplify.c (gimplify_switch_expr): Implement the -Wswitch-unreachable
+	warning.
+
+2016-05-23  Bin Cheng  <bin.cheng@arm.com>
 
 	* tree-ssa-address.c (copy_ref_info): Check NULL TMR_STEP when
 	TMR_INDEX is non-NULL.

gcc/common.opt

@@ -707,6 +707,11 @@ Wsuggest-final-methods
 Common Var(warn_suggest_final_methods) Warning
 Warn about C++ virtual methods where adding final keyword would improve code quality.
 
+Wswitch-unreachable
+Common Var(warn_switch_unreachable) Warning Init(1)
+Warn about statements between switch's controlling expression and the first
+case.
+
 Wsystem-headers
 Common Var(warn_system_headers) Warning
 Do not suppress warnings from system headers.

gcc/doc/invoke.texi

@@ -297,7 +297,8 @@ Objective-C and Objective-C++ Dialects}.
 -Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{|}format@r{]} @gol
 -Wsuggest-final-types @gol -Wsuggest-final-methods -Wsuggest-override @gol
 -Wmissing-format-attribute -Wsubobject-linkage @gol
--Wswitch  -Wswitch-default  -Wswitch-enum -Wswitch-bool -Wsync-nand @gol
+-Wswitch  -Wswitch-bool  -Wswitch-default  -Wswitch-enum @gol
+-Wswitch-unreachable  -Wsync-nand @gol
 -Wsystem-headers  -Wtautological-compare  -Wtrampolines  -Wtrigraphs @gol
 -Wtype-limits  -Wundef @gol
 -Wuninitialized  -Wunknown-pragmas  -Wunsafe-loop-optimizations @gol
@@ -4144,6 +4145,39 @@ switch ((int) (a == 4))
 @end smallexample
 This warning is enabled by default for C and C++ programs.
 
+@item -Wswitch-unreachable
+@opindex Wswitch-unreachable
+@opindex Wno-switch-unreachable
+Warn whenever a @code{switch} statement contains statements between the
+controlling expression and the first case label, which will never be
+executed.  For example:
+@smallexample
+@group
+switch (cond)
+  @{
+   i = 15;
+  @dots{}
+   case 5:
+  @dots{}
+  @}
+@end group
+@end smallexample
+@option{-Wswitch-unreachable} does not warn if the statement between the
+controlling expression and the first case label is just a declaration:
+@smallexample
+@group
+switch (cond)
+  @{
+   int i;
+  @dots{}
+   case 5:
+   i = 5;
+  @dots{}
+  @}
+@end group
+@end smallexample
+This warning is enabled by default for C and C++ programs.
+
 @item -Wsync-nand @r{(C and C++ only)}
 @opindex Wsync-nand
 @opindex Wno-sync-nand

gcc/gimplify.c

@@ -1595,6 +1595,32 @@ gimplify_switch_expr (tree *expr_p, gimple_seq *pre_p)
       gimplify_ctxp->case_labels.create (8);
 
       gimplify_stmt (&SWITCH_BODY (switch_expr), &switch_body_seq);
+
+      /* Possibly warn about unreachable statements between switch's
+	 controlling expression and the first case.  */
+      if (warn_switch_unreachable
+	  /* This warning doesn't play well with Fortran when optimizations
+	     are on.  */
+	  && !lang_GNU_Fortran ()
+	  && switch_body_seq != NULL)
+	{
+	  gimple_seq seq = switch_body_seq;
+	  if (gimple_code (switch_body_seq) == GIMPLE_BIND)
+	    seq = gimple_bind_body (as_a <gbind *> (switch_body_seq));
+	  gimple *stmt = gimple_seq_first_stmt (seq);
+	  enum gimple_code code = gimple_code (stmt);
+	  if (code != GIMPLE_LABEL && code != GIMPLE_TRY)
+	    {
+	      if (code == GIMPLE_GOTO
+		  && TREE_CODE (gimple_goto_dest (stmt)) == LABEL_DECL
+		  && DECL_ARTIFICIAL (gimple_goto_dest (stmt)))
+		/* Don't warn for compiler-generated gotos.  These occur
+		   in Duff's devices, for example.  */;
+	      else
+		warning_at (gimple_location (stmt), OPT_Wswitch_unreachable,
+			    "statement will never be executed");
+	    }
+	}
       labels = gimplify_ctxp->case_labels;
       gimplify_ctxp->case_labels = saved_labels;
 

gcc/testsuite/ChangeLog

+2016-05-23  Marek Polacek  <polacek@redhat.com>
+
+	PR c/49859
+	* c-c++-common/Wswitch-unreachable-1.c: New test.
+	* gcc.dg/Wswitch-unreachable-1.c: New test.
+	* c-c++-common/goacc/sb-2.c (void foo): Add dg-warning.
+	* g++.dg/cpp0x/lambda/lambda-switch.C (main): Likewise.
+	* g++.dg/gomp/block-10.C: Likewise.
+	* gcc.dg/gomp/block-10.c: Likewise.
+	* g++.dg/gomp/block-9.C: Likewise.
+	* gcc.dg/gomp/block-9.c: Likewise.
+	* g++.dg/gomp/target-1.C: Likewise.
+	* g++.dg/gomp/target-2.C: Likewise.
+	* gcc.dg/gomp/target-1.c: Likewise.
+	* gcc.dg/gomp/target-2.c: Likewise. 
+	* g++.dg/gomp/taskgroup-1.C: Likewise.
+	* gcc.dg/gomp/taskgroup-1.c: Likewise.
+	* gcc.dg/gomp/teams-1.c: Likewise.
+	* g++.dg/gomp/teams-1.C: Likewise.
+	* g++.dg/overload/error3.C: Likewise.
+	* g++.dg/tm/jump1.C: Likewise.
+	* g++.dg/torture/pr40335.C: Likewise.
+	* gcc.dg/c99-vla-jump-5.c: Likewise.
+	* gcc.dg/switch-warn-1.c: Likewise.
+	* gcc.dg/Wjump-misses-init-1.c: Use -Wno-switch-unreachable.
+	* gcc.dg/nested-func-1.c: Likewise.
+	* gcc.dg/pr67784-4.c: Likewise.
+
 2016-05-23  Richard Biener  <rguenther@suse.de>
 
 	PR tree-optimization/71230

gcc/testsuite/c-c++-common/Wswitch-unreachable-1.c

+/* PR c/49859 */
+/* { dg-do compile } */
+
+extern void foo (int);
+extern int j;
+
+void
+fn0 (int i)
+{
+  switch (i)
+    {
+    int k;
+    case 1:
+      k = 11;
+      foo (k);
+    }
+
+  switch (i)
+    j = 10; /* { dg-warning "statement will never be executed" } */
+
+  switch (i)
+    ;
+
+  switch (i)
+    {
+    j = 12; /* { dg-warning "statement will never be executed" } */
+    default:
+      foo (j);
+    }
+
+  int o;
+  switch (i)
+    {
+    o = 333; /* { dg-warning "statement will never be executed" } */
+    case 4: break;
+    default:
+      foo (o);
+    }
+
+  switch (i)
+    switch (j) /* { dg-warning "statement will never be executed" } */
+      {
+      o = 42; /* { dg-warning "statement will never be executed" } */
+      case 8:;
+      }
+
+  switch (i)
+    {
+      int l = 3; /* { dg-warning "statement will never be executed" } */
+      o = 5;
+      j = 7;
+      ++l;
+    }
+
+  switch (i)
+    {
+      int x;
+      int l = 3; /* { dg-warning "statement will never be executed" } */
+      ++l, ++x;
+    }
+
+  switch (i)
+    if (j != 3) /* { dg-warning "statement will never be executed" } */
+      foo (j);
+
+  switch (i)
+    while (1)
+     foo (0);
+
+  switch (i)
+    while (i > 5) { }
+
+  switch (i)
+    goto X; /* { dg-warning "statement will never be executed" } */
+X:
+
+  switch (i)
+    do
+      foo (1);
+    while (1);
+
+  switch (i)
+    for (;;)
+      foo (-1);
+
+  switch (i)
+    default:
+      j = 6;
+
+  switch (i)
+    {
+    typedef int T;
+    case 3:
+      {
+	T x = 5;
+	foo (x);
+      }
+    }
+
+  switch (i)
+    {
+      static int g;
+      default:
+	foo (g);
+    }
+
+  switch (i)
+    {
+L:
+      j = 16;
+      default:
+	if (j < 5)
+	  goto L;
+	break;
+    }
+}

gcc/testsuite/c-c++-common/goacc/sb-2.c

@@ -4,19 +4,19 @@ void foo(int i)
 {
   switch (i) // { dg-error "invalid entry to OpenACC structured block" }
   {
-  #pragma acc parallel
+  #pragma acc parallel // { dg-warning "statement will never be executed" }
     { case 0:; }
   }
 
   switch (i) // { dg-error "invalid entry to OpenACC structured block" }
   {
-  #pragma acc kernels
+  #pragma acc kernels // { dg-warning "statement will never be executed" }
     { case 0:; }
   }
 
   switch (i) // { dg-error "invalid entry to OpenACC structured block" }
   {
-  #pragma acc data
+  #pragma acc data // { dg-warning "statement will never be executed" }
     { case 0:; }
   }
 }

gcc/testsuite/g++.dg/cpp0x/lambda/lambda-switch.C

@@ -20,7 +20,7 @@ main ()
 	    {
 	    case 3:		// { dg-error "case" }
 	      break;		// { dg-error "break" }
-	    };
+	    };			// { dg-warning "statement will never be executed" }
 	}
     }
 }

gcc/testsuite/g++.dg/gomp/block-10.C

@@ -5,28 +5,28 @@ void foo(int i)
   int j;
   switch (i)
   {
-  #pragma omp parallel
+  #pragma omp parallel	// { dg-warning "statement will never be executed" }
     { case 0:; }	// { dg-error "jump|enters" }
   }
   switch (i)
   {
-  #pragma omp for
+  #pragma omp for	// { dg-warning "statement will never be executed" }
     for (j = 0; j < 10; ++ j)
       { case 1:; }	// { dg-error "jump|enters" }
   }
   switch (i)
   {
-  #pragma omp critical
+  #pragma omp critical	// { dg-warning "statement will never be executed" }
     { case 2:; }	// { dg-error "jump|enters" }
   }
   switch (i)
   {
-  #pragma omp master
+  #pragma omp master	// { dg-warning "statement will never be executed" }
     { case 3:; }	// { dg-error "jump|enters" }
   }
   switch (i)
   {
-  #pragma omp sections
+  #pragma omp sections	// { dg-warning "statement will never be executed" }
     { case 4:;		// { dg-error "jump|enters" }
     #pragma omp section
        { case 5:; }	// { dg-error "jump|enters" }
@@ -34,7 +34,7 @@ void foo(int i)
   }
   switch (i)
   {
-  #pragma omp ordered
+  #pragma omp ordered	// { dg-warning "statement will never be executed" }
     { default:; }	// { dg-error "jump|enters" }
   }
 }

gcc/testsuite/g++.dg/gomp/block-9.C

@@ -5,7 +5,7 @@ void foo(int i)
   int j;
   switch (i)
   {
-  #pragma omp parallel
+  #pragma omp parallel		// { dg-warning "statement will never be executed" }
     { case 0:; }		// { dg-error "jump|enters" }
   #pragma omp for
     for (j = 0; j < 10; ++ j)

gcc/testsuite/g++.dg/gomp/target-1.C

@@ -24,7 +24,7 @@ foo (int x)
 
   switch (x)
   {
-  #pragma omp target
+  #pragma omp target		// { dg-warning "statement will never be executed" }
     { case 0:; }		// { dg-error "jump" }
                                 // { dg-message "enters" "" { target *-*-* } 28 }
   }

gcc/testsuite/g++.dg/gomp/target-2.C

@@ -24,7 +24,7 @@ foo (int x, int y)
 
   switch (x)
   {
-  #pragma omp target data map(tofrom: y)
+  #pragma omp target data map(tofrom: y) // { dg-warning "statement will never be executed" }
     { case 0:; }		// { dg-error "jump" }
                                 // { dg-message "enters" "" { target *-*-* } 28 }
   }

gcc/testsuite/g++.dg/gomp/taskgroup-1.C

@@ -24,7 +24,7 @@ foo (int x)
 
   switch (x)
   {
-  #pragma omp taskgroup
+  #pragma omp taskgroup		// { dg-warning "statement will never be executed" }
     { case 0:; }		// { dg-error "jump" }
                                 // { dg-message "enters" "" { target *-*-* } 28 }
   }

gcc/testsuite/g++.dg/gomp/teams-1.C

@@ -26,6 +26,7 @@ foo (int x)
   {
   #pragma omp target teams
     { case 0:; }		// { dg-error "jump" }
+				// { dg-warning "statement will never be executed" "" { target *-*-* } 28 }
                                 // { dg-message "enters" "" { target *-*-* } 28 }
   }
 }
@@ -43,7 +44,7 @@ bar (int x)
   #pragma omp teams
     {
       bad2: ;			// { dg-error "jump to label" }
-                                // { dg-message "enters OpenMP" "" { target *-*-* } 45 }
+                                // { dg-message "enters OpenMP" "" { target *-*-* } 46 }
     }
 
   #pragma omp target
@@ -57,14 +58,14 @@ bar (int x)
 
   switch (x)
   {
-  #pragma omp target
+  #pragma omp target		// { dg-warning "statement will never be executed" }
   #pragma omp teams
     { case 0:; }		// { dg-error "jump" }
-                                // { dg-message "enters" "" { target *-*-* } 62 }
+                                // { dg-message "enters" "" { target *-*-* } 63 }
   }
 }
 
 // { dg-error "invalid branch to/from OpenMP structured block" "" { target *-*-* } 8 }
 // { dg-error "invalid entry to OpenMP structured block" "" { target *-*-* } 10 }
-// { dg-error "invalid branch to/from OpenMP structured block" "" { target *-*-* } 39 }
-// { dg-error "invalid entry to OpenMP structured block" "" { target *-*-* } 41 }
+// { dg-error "invalid branch to/from OpenMP structured block" "" { target *-*-* } 40 }
+// { dg-error "invalid entry to OpenMP structured block" "" { target *-*-* } 42 }

gcc/testsuite/g++.dg/overload/error3.C

@@ -35,6 +35,7 @@ class MainWindow  {
 void MainWindow::update_status(Result result) {
     switch (result) {
         status_frame.modify_bg(Gtk::STATE_NORMAL,Gdk::Color::Color("green")); // { dg-error "" }
+	// { dg-warning "statement will never be executed" "" { target *-*-* } 37 }
         status_frame.modify_bg(Gtk::STATE_NORMAL,Gdk::Color::Color("red")); // { dg-error "" }
         status_label.set_text("Out of memory");
     }

gcc/testsuite/g++.dg/tm/jump1.C

@@ -14,7 +14,7 @@ void f()
 
   switch (i)
     {
-      synchronized {
+      synchronized {		// { dg-warning "statement will never be executed" }
 	++i;
       case 42:			// { dg-error "" }
 	++i;

gcc/testsuite/g++.dg/torture/pr40335.C

@@ -8,7 +8,7 @@ main (void)
   switch ((signed char) i)
     {
       case 255: /* { dg-bogus "exceeds maximum value" "" { xfail *-*-* } } */
-	abort ();
+	abort (); /* { dg-warning "statement will never be executed" } */
       default:
 	break;
     }

gcc/testsuite/gcc.dg/Wjump-misses-init-1.c

 /* { dg-do compile } */
-/* { dg-options "-Wjump-misses-init" } */
+/* { dg-options "-Wjump-misses-init -Wno-switch-unreachable" } */
 int
 f1 (int a)
 {

gcc/testsuite/gcc.dg/Wswitch-unreachable-1.c

+/* PR c/49859 */
+/* { dg-do compile } */
+/* { dg-options "-Wswitch-unreachable" } */
+
+extern void foo (int);
+extern int j;
+
+void
+fn0 (int i)
+{
+  switch (i)
+    {
+    int t = 10; /* { dg-warning "statement will never be executed" } */
+    default:
+      foo (t);
+    }
+
+  switch (i)
+    { /* { dg-warning "statement will never be executed" } */
+      int A[i];
+      default: /* { dg-error "switch jumps into scope" } */
+	break;
+    }
+
+  switch (i)
+    default:
+      j = sizeof (struct { int i; });
+
+  switch (i)
+    {
+      int A[3];
+      default:
+	break;
+    }
+}

gcc/testsuite/gcc.dg/c99-vla-jump-5.c

@@ -14,7 +14,7 @@
 void
 f (int a, int b)
 {
-  switch (a) {
+  switch (a) { /* { dg-warning "statement will never be executed" } */
     int v[b];
   case 2: /* { dg-error "switch jumps into scope of identifier with variably modified type" } */
   default: /* { dg-error "switch jumps into scope of identifier with variably modified type" } */

gcc/testsuite/gcc.dg/gomp/block-10.c

@@ -5,28 +5,28 @@ void foo(int i)
   int j;
   switch (i) // { dg-error "invalid entry to OpenMP structured block" }
   {
-  #pragma omp parallel
+  #pragma omp parallel // { dg-warning "statement will never be executed" }
     { case 0:; }
   }
   switch (i) // { dg-error "invalid entry to OpenMP structured block" }
   {
-  #pragma omp for
+  #pragma omp for // { dg-warning "statement will never be executed" }
     for (j = 0; j < 10; ++ j)
       { case 1:; }
   }
   switch (i) // { dg-error "invalid entry to OpenMP structured block" }
   {
-  #pragma omp critical
+  #pragma omp critical // { dg-warning "statement will never be executed" }
     { case 2:; }
   }
   switch (i) // { dg-error "invalid entry to OpenMP structured block" }
   {
-  #pragma omp master
+  #pragma omp master // { dg-warning "statement will never be executed" }
     { case 3:; }
   }
   switch (i) // { dg-error "invalid entry to OpenMP structured block" }
   {
-  #pragma omp sections
+  #pragma omp sections // { dg-warning "statement will never be executed" }
     { case 4:;
     #pragma omp section
        { case 5:; }
@@ -34,7 +34,7 @@ void foo(int i)
   }
   switch (i) // { dg-error "invalid entry to OpenMP structured block" }
   {
-  #pragma omp ordered
+  #pragma omp ordered // { dg-warning "statement will never be executed" }
     { default:; }
   }
 }

gcc/testsuite/gcc.dg/gomp/block-9.c

@@ -5,7 +5,7 @@ void foo(int i)
   int j;
   switch (i) // { dg-error "invalid entry to OpenMP structured block" }
   {
-  #pragma omp parallel
+  #pragma omp parallel // { dg-warning "statement will never be executed" }
     { case 0:; }
   #pragma omp for
     for (j = 0; j < 10; ++ j)

gcc/testsuite/gcc.dg/gomp/target-1.c

@@ -23,7 +23,7 @@ foo (int x)
 
   switch (x) // { dg-error "invalid entry to OpenMP structured block" }
   {
-  #pragma omp target
+  #pragma omp target // { dg-warning "statement will never be executed" }
     { case 0:; }
   }
 }

gcc/testsuite/gcc.dg/gomp/target-2.c

@@ -23,7 +23,7 @@ foo (int x, int y)
 
   switch (x) // { dg-error "invalid entry to OpenMP structured block" }
   {
-  #pragma omp target data map(tofrom: y)
+  #pragma omp target data map(tofrom: y) // { dg-warning "statement will never be executed" }
     { case 0:; }
   }
 }

gcc/testsuite/gcc.dg/gomp/taskgroup-1.c

@@ -23,7 +23,7 @@ foo (int x)
 
   switch (x) // { dg-error "invalid entry to OpenMP structured block" }
   {
-  #pragma omp taskgroup
+  #pragma omp taskgroup // { dg-warning "statement will never be executed" }
     { case 0:; }
   }
 }

gcc/testsuite/gcc.dg/gomp/teams-1.c

@@ -24,7 +24,7 @@ foo (int x)
   switch (x) // { dg-error "invalid entry to OpenMP structured block" }
   {
   #pragma omp target teams
-    { case 0:; }
+    { case 0:; } // { dg-warning "statement will never be executed" }
   }
 }
 
@@ -54,7 +54,7 @@ bar (int x)
 
   switch (x) // { dg-error "invalid entry to OpenMP structured block" }
   {
-  #pragma omp target
+  #pragma omp target // { dg-warning "statement will never be executed" }
   #pragma omp teams
     { case 0:; }
   }

gcc/testsuite/gcc.dg/nested-func-1.c

 /* Test for proper errors for break and continue in nested functions.  */
 /* Origin: Joseph Myers <jsm@polyomino.org.uk> */
 /* { dg-do compile } */
-/* { dg-options "" } */
+/* { dg-options "-Wno-switch-unreachable" } */
 
 void
 foo (int a)

gcc/testsuite/gcc.dg/pr67784-4.c

 /* PR c/67784 */
 /* { dg-do compile } */
-/* { dg-options "" } */
+/* { dg-options "-Wno-switch-unreachable" } */
 
 typedef int T;
 

gcc/testsuite/gcc.dg/switch-warn-1.c

@@ -11,7 +11,7 @@ foo1 (unsigned char i)
 {
   switch (i)
     {
-    case -1:   /* { dg-warning "case label value is less than minimum value for type" } */
+    case -1:   /* { dg-warning "case label value is less than minimum value for type|statement will never be executed" } */
       return 1;
     case 256:  /* { dg-warning "case label value exceeds maximum value for type" } */
       return 2;