Some low-hanging -Wunreachable-code fruits.

- after croak/die/exit (or return), break (or return!) are pointless
  (break is not a terminator/separator, it's a promise of a jump)
- after goto, another goto (!) is pointless
- in some cases (usually function ends) introduce explicit NOT_REACHED
  to make the noreturn nature clearer (do not do this everywhere, though,
  since that would mean adding NOT_REACHED after every croak)
- for the added NOT_REACHED also add /* NOTREACHED */ since
  NOT_REACHED is for gcc (and VC), while the comment is for linters
- declaring variables in switch blocks is just too fragile:
  it kind of works for narrowing the scope (which is nice),
  but breaks the moment there are initializations for the variables
  (they will be skipped!); in some easy cases simply hoist the declarations
  out of the block and move them earlier

There are still a few places left.

16 files changed, 53 insertions, 61 deletions

diff --git a/dump.c b/dump.c
index 9bbbe2dd17..888866c11b 100644
--- a/dump.c
+++ b/dump.c
@@ -2379,6 +2379,7 @@ I32
 Perl_debop(pTHX_ const OP *o)
 {
     dVAR;
+    int count;
 
     PERL_ARGS_ASSERT_DEBOP;
 
@@ -2410,9 +2411,6 @@ Perl_debop(pTHX_ const OP *o)
 	    PerlIO_printf(Perl_debug_log, "(NULL)");
 	break;
 
-    {
-        int count;
-
     case OP_PADSV:
     case OP_PADAV:
     case OP_PADHV:
@@ -2446,7 +2444,6 @@ Perl_debop(pTHX_ const OP *o)
             PerlIO_printf(Perl_debug_log, ")");
         }
         break;
-    }
 
     default:
 	break;
diff --git a/ext/ExtUtils-Miniperl/lib/ExtUtils/Miniperl.pm b/ext/ExtUtils-Miniperl/lib/ExtUtils/Miniperl.pm
index cede3180f8..94927afbe1 100644
--- a/ext/ExtUtils-Miniperl/lib/ExtUtils/Miniperl.pm
+++ b/ext/ExtUtils-Miniperl/lib/ExtUtils/Miniperl.pm
@@ -191,7 +191,6 @@ main(int argc, char **argv, char **env)
 #endif /* PERL_GLOBAL_STRUCT */
 
     exit(exitstatus);
-    return exitstatus;
 }
 
 /* Register any extra external extensions */
diff --git a/gv.c b/gv.c
index b4ad5231a2..1ef1155372 100644
--- a/gv.c
+++ b/gv.c
@@ -352,7 +352,7 @@ Perl_gv_init_pvn(pTHX_ GV *gv, HV *stash, const char *name, STRLEN len, U32 flag
 	case SVt_PVIO:
             Perl_croak(aTHX_ "Cannot convert a reference to %s to typeglob",
 		       sv_reftype(has_constant, 0));
-            break;
+
 	default: NOOP;
 	}
 	SvRV_set(gv, NULL);
@@ -2969,7 +2969,7 @@ Perl_amagic_call(pTHX_ SV *left, SV *right, int method, int flags)
 	 case regexp_amg:
 	     /* FAIL safe */
 	     return NULL;	/* Delegate operation to standard mechanisms. */
-	     break;
+
 	 case to_sv_amg:
 	 case to_av_amg:
 	 case to_hv_amg:
@@ -2977,7 +2977,7 @@ Perl_amagic_call(pTHX_ SV *left, SV *right, int method, int flags)
 	 case to_cv_amg:
 	     /* FAIL safe */
 	     return left;	/* Delegate operation to standard mechanisms. */
-	     break;
+
 	 default:
 	   goto not_found;
 	 }
@@ -3044,7 +3044,6 @@ Perl_amagic_call(pTHX_ SV *left, SV *right, int method, int flags)
 	 case to_cv_amg:
 	     /* FAIL safe */
 	     return left;	/* Delegate operation to standard mechanisms. */
-	     break;
       }
       if (ocvp && (cv=ocvp[nomethod_amg])) { /* Call report method */
 	notfound = 1; lr = -1;
diff --git a/mg.c b/mg.c
index 63d0d612b6..bd09ff6382 100644
--- a/mg.c
+++ b/mg.c
@@ -348,9 +348,9 @@ Perl_mg_size(pTHX_ SV *sv)
 	    /* FIXME */
 	default:
 	    Perl_croak(aTHX_ "Size magic not implemented");
-	    break;
+
     }
-    return 0;
+    NOT_REACHED; /* NOTREACHED */
 }
 
 /*
diff --git a/miniperlmain.c b/miniperlmain.c
index f22dcbba8d..e748523414 100644
--- a/miniperlmain.c
+++ b/miniperlmain.c
@@ -162,7 +162,6 @@ main(int argc, char **argv, char **env)
 #endif /* PERL_GLOBAL_STRUCT */
 
     exit(exitstatus);
-    return exitstatus;
 }
 
 /* Register any extra external extensions */
diff --git a/op.c b/op.c
index eb64b52b8e..eea56f8872 100644
--- a/op.c
+++ b/op.c
@@ -1071,7 +1071,6 @@ Perl_op_contextualize(pTHX_ OP *o, I32 context)
 	default:
 	    Perl_croak(aTHX_ "panic: op_contextualize bad context %ld",
 		       (long) context);
-	    return o;
     }
 }
 
@@ -9818,7 +9817,7 @@ Perl_rv2cv_op_cv(pTHX_ OP *cvop, U32 flags)
 	} break;
 	default: {
 	    return NULL;
-	} break;
+	} NOT_REACHED; /* NOTREACHED */
     }
     if (SvTYPE((SV*)cv) != SVt_PVCV)
 	return NULL;
@@ -9995,7 +9994,7 @@ Perl_ck_entersub_args_proto(pTHX_ OP *entersubop, GV *namegv, SV *protosv)
 		break;
 	    case '[': case ']':
 		goto oops;
-		break;
+
 	    case '\\':
 		proto++;
 		arg++;
@@ -10010,7 +10009,7 @@ Perl_ck_entersub_args_proto(pTHX_ OP *entersubop, GV *namegv, SV *protosv)
 			else
 			    goto oops;
 			goto again;
-			break;
+
 		    case ']':
 			if (contextclass) {
 			    const char *p = proto;
@@ -10704,6 +10703,8 @@ Perl_rpeep(pTHX_ OP *o)
     OP** defer_queue[MAX_DEFERRED]; /* small queue of deferred branches */
     int defer_base = 0;
     int defer_ix = -1;
+    OP *fop;
+    OP *sop;
 
     if (!o || o->op_opt)
 	return;
@@ -11277,10 +11278,6 @@ Perl_rpeep(pTHX_ OP *o)
 
 	    break;
         
-        {
-            OP *fop;
-            OP *sop;
-            
 #define HV_OR_SCALARHV(op)                                   \
     (  (op)->op_type == OP_PADHV || (op)->op_type == OP_RV2HV \
        ? (op)                                                  \
@@ -11366,8 +11363,7 @@ Perl_rpeep(pTHX_ OP *o)
 	    if ((fop = HV_OR_SCALARHV(cLOGOP->op_first)))
 		fop->op_private |= OPpTRUEBOOL;
 #undef HV_OR_SCALARHV
-	    /* GERONIMO! */
-	}    
+	    /* GERONIMO! */ /* FALLTHROUGH */
 
 	case OP_MAPWHILE:
 	case OP_GREPWHILE:
diff --git a/pp.c b/pp.c
index 9d19c91839..f544c39a94 100644
--- a/pp.c
+++ b/pp.c
@@ -226,8 +226,9 @@ S_rv2gv(pTHX_ SV *sv, const bool vivify_sv, const bool strict,
 	    SvREFCNT_inc_void_NN(sv);
 	    sv = MUTABLE_SV(gv);
 	}
-	else if (!isGV_with_GP(sv))
-	    return (SV *)Perl_die(aTHX_ "Not a GLOB reference");
+	else if (!isGV_with_GP(sv)) {
+	    Perl_die(aTHX_ "Not a GLOB reference");
+        }
     }
     else {
 	if (!isGV_with_GP(sv)) {
@@ -257,8 +258,9 @@ S_rv2gv(pTHX_ SV *sv, const bool vivify_sv, const bool strict,
 		    SvSETMAGIC(sv);
 		    goto wasref;
 		}
-		if (PL_op->op_flags & OPf_REF || strict)
-		    return (SV *)Perl_die(aTHX_ PL_no_usym, "a symbol");
+		if (PL_op->op_flags & OPf_REF || strict) {
+		    Perl_die(aTHX_ PL_no_usym, "a symbol");
+                }
 		if (ckWARN(WARN_UNINITIALIZED))
 		    report_uninit(sv);
 		return &PL_sv_undef;
@@ -271,14 +273,14 @@ S_rv2gv(pTHX_ SV *sv, const bool vivify_sv, const bool strict,
 		    return &PL_sv_undef;
 	    }
 	    else {
-		if (strict)
-		    return
-		     (SV *)Perl_die(aTHX_
-		            S_no_symref_sv,
-		            sv,
-		            (SvPOKp(sv) && SvCUR(sv)>32 ? "..." : ""),
-		            "a symbol"
-		           );
+		if (strict) {
+                    Perl_die(aTHX_
+                             S_no_symref_sv,
+                             sv,
+                             (SvPOKp(sv) && SvCUR(sv)>32 ? "..." : ""),
+                             "a symbol"
+                             );
+                }
 		if ((PL_op->op_private & (OPpLVAL_INTRO|OPpDONT_INIT_GV))
 		    == OPpDONT_INIT_GV) {
 		    /* We are the target of a coderef assignment.  Return
diff --git a/pp_ctl.c b/pp_ctl.c
index ab729b0334..8957a8ceed 100644
--- a/pp_ctl.c
+++ b/pp_ctl.c
@@ -1357,9 +1357,8 @@ Perl_block_gimme(pTHX)
 	return G_ARRAY;
     default:
 	Perl_croak(aTHX_ "panic: bad gimme: %d\n", cxstack[cxix].blk_gimme);
-	assert(0); /* NOTREACHED */
-	return 0;
     }
+    NOT_REACHED; /* NOTREACHED */
 }
 
 I32
@@ -4336,8 +4335,8 @@ PP(pp_leaveeval)
 			SvPVX_const(namesv),
                         SvUTF8(namesv) ? -(I32)SvCUR(namesv) : (I32)SvCUR(namesv),
 			G_DISCARD);
-	retop = Perl_die(aTHX_ "%"SVf" did not return a true value",
-			       SVfARG(namesv));
+	Perl_die(aTHX_ "%"SVf" did not return a true value", SVfARG(namesv));
+        NOT_REACHED; /* NOTREACHED */
 	/* die_unwind() did LEAVE, or we won't be here */
     }
     else {
diff --git a/pp_pack.c b/pp_pack.c
index 998982d77c..f877fe21af 100644
--- a/pp_pack.c
+++ b/pp_pack.c
@@ -448,7 +448,7 @@ S_measure_struct(pTHX_ tempsym_t* symptr)
 	  case e_star:
    	    Perl_croak(aTHX_ "Within []-length '*' not allowed in %s",
                         _action( symptr ) );
-            break;
+
 	  default:
 	    /* e_no_len and e_number */
 	    len = symptr->length;
@@ -567,7 +567,7 @@ S_group_end(pTHX_ const char *patptr, const char *patend, char ender)
     }
     Perl_croak(aTHX_ "No group ending character '%c' found in template",
                ender);
-    return 0;
+    NOT_REACHED; /* NOTREACHED */
 }
 
 
@@ -934,7 +934,7 @@ S_unpack_rec(pTHX_ tempsym_t* symptr, const char *s, const char *strbeg, const c
 	    cuv = 0;
 	    cdouble = 0;
 	    continue;
-	    break;
+
 	case '(':
 	{
             tempsym_t savsym = *symptr;
@@ -1060,7 +1060,7 @@ S_unpack_rec(pTHX_ tempsym_t* symptr, const char *s, const char *strbeg, const c
 	    break;
 	case '/':
 	    Perl_croak(aTHX_ "'/' must follow a numeric type in unpack");
-            break;
+
 	case 'A':
 	case 'Z':
 	case 'a':
@@ -2083,6 +2083,7 @@ S_pack_rec(pTHX_ SV *cat, tempsym_t* symptr, SV **beglist, SV **endlist )
     bool found = next_symbol(symptr);
     bool utf8 = (symptr->flags & FLAG_PARSE_UTF8) ? 1 : 0;
     bool warn_utf8 = ckWARN(WARN_UTF8);
+    char* from;
 
     PERL_ARGS_ASSERT_PACK_REC;
 
@@ -2163,8 +2164,7 @@ S_pack_rec(pTHX_ SV *cat, tempsym_t* symptr, SV **beglist, SV **endlist )
 		       (int) TYPE_NO_MODIFIERS(datumtype));
 	case '%':
 	    Perl_croak(aTHX_ "'%%' may not be used in pack");
-	{
-	    char *from;
+
 	case '.' | TYPE_IS_SHRIEKING:
 	case '.':
 	    if (howlen == e_star) from = start;
@@ -2213,7 +2213,7 @@ S_pack_rec(pTHX_ SV *cat, tempsym_t* symptr, SV **beglist, SV **endlist )
 		goto shrink;
 	    }
 	    break;
-	}
+
 	case '(': {
             tempsym_t savsym = *symptr;
 	    U32 group_modifiers = TYPE_MODIFIERS(datumtype & ~symptr->flags);
diff --git a/pp_sys.c b/pp_sys.c
index 18b3d8ebf7..ca6bbe7fd2 100644
--- a/pp_sys.c
+++ b/pp_sys.c
@@ -519,7 +519,8 @@ PP(pp_die)
 	    exsv = newSVpvs_flags("Died", SVs_TEMP);
 	}
     }
-    return die_sv(exsv);
+    die_sv(exsv);
+    NOT_REACHED; /* NOTREACHED */
 }
 
 /* I/O. */
diff --git a/regcomp.c b/regcomp.c
index 205c840b42..cafc670f12 100644
--- a/regcomp.c
+++ b/regcomp.c
@@ -9472,6 +9472,7 @@ S_reg(pTHX_ RExC_state_t *pRExC_state, I32 paren, I32 *flagp,U32 depth)
     bool is_open = 0;
     I32 freeze_paren = 0;
     I32 after_freeze = 0;
+    I32 num; /* numeric backreferences */
 
     char * parse_start = RExC_parse; /* MJD */
     char * const oregcomp_parse = RExC_parse;
@@ -9789,8 +9790,7 @@ S_reg(pTHX_ RExC_state_t *pRExC_state, I32 paren, I32 *flagp,U32 depth)
 		nextchar(pRExC_state);
 		return ret;
 		/*notreached*/
-            { /* named and numeric backreferences */
-                I32 num;
+            /* named and numeric backreferences */
             case '&':            /* (?&NAME) */
                 parse_start = RExC_parse - 1;
               named_recursion:
@@ -9872,7 +9872,7 @@ S_reg(pTHX_ RExC_state_t *pRExC_state, I32 paren, I32 *flagp,U32 depth)
                 *flagp |= POSTPONED;
                 nextchar(pRExC_state);
                 return ret;
-            } /* named and numeric backreferences */
+
             assert(0); /* NOT REACHED */
 
 	    case '?':           /* (??...) */
@@ -11245,6 +11245,7 @@ S_regatom(pTHX_ RExC_state_t *pRExC_state, I32 *flagp, U32 depth)
     char *parse_start = RExC_parse;
     U8 op;
     int invert = 0;
+    U8 arg;
 
     GET_RE_DEBUG_FLAGS_DECL;
 
@@ -11361,7 +11362,6 @@ tryagain:
 	   literal text handling code.
 	*/
 	switch ((U8)*++RExC_parse) {
-            U8 arg;
 	/* Special Escapes */
 	case 'A':
 	    RExC_seen_zerolen++;
diff --git a/regexec.c b/regexec.c
index 0855bad69c..000653a773 100644
--- a/regexec.c
+++ b/regexec.c
@@ -2258,7 +2258,6 @@ S_find_byclass(pTHX_ regexp * prog, const regnode *c, char *s,
         break;
     default:
         Perl_croak(aTHX_ "panic: unknown regstclass %d", (int)OP(c));
-        break;
     }
     return 0;
   got_it:
@@ -2455,7 +2454,6 @@ Perl_regexec_flags(pTHX_ REGEXP * const rx, char *stringarg, char *strend,
     /* Be paranoid... */
     if (prog == NULL || stringarg == NULL) {
 	Perl_croak(aTHX_ "NULL regexp parameter");
-	return 0;
     }
 
     DEBUG_EXECUTE_r(
@@ -4618,7 +4616,6 @@ S_regmatch(pTHX_ regmatch_info *reginfo, char *startpos, regnode *prog)
 			break;
 		    default:
 			Perl_croak(aTHX_ "panic: Unexpected FLAGS %u in op %u", FLAGS(scan), OP(scan));
-			break;
 		}
 	    }
 	    /* Note requires that all BOUNDs be lower than all NBOUNDs in
diff --git a/regexp.h b/regexp.h
index db7ae8be01..3295c4a293 100644
--- a/regexp.h
+++ b/regexp.h
@@ -381,9 +381,9 @@ get_regex_charset_name(const U32 flags, STRLEN* const lenp)
 	case REGEX_ASCII_MORE_RESTRICTED_CHARSET:
 	    *lenp = 2;
 	    return ASCII_MORE_RESTRICT_PAT_MODS;
-        default:
-	    return "?";	    /* Unknown */
     }
+    NOT_REACHED; /* NOTREACHED */
+    return "?";
 }
 
 /* Do we have some sort of anchor? */
diff --git a/sv.c b/sv.c
index 05f26d76e0..77c213ef0d 100644
--- a/sv.c
+++ b/sv.c
@@ -4215,7 +4215,7 @@ Perl_sv_setsv_flags(pTHX_ SV *dstr, SV* sstr, const I32 flags)
 	else
 	    Perl_croak(aTHX_ "Bizarre copy of %s", type);
 	}
-	break;
+	NOT_REACHED; /* NOTREACHED */
 
     case SVt_REGEXP:
       upgregexp:
@@ -11346,10 +11346,10 @@ Perl_sv_vcatpvfn_flags(pTHX_ SV *const sv, const char *const pat, const STRLEN p
 	    {
 		char *ptr = ebuf + sizeof ebuf;
 		bool tempalt = uv ? alt : FALSE; /* Vectors can't change alt */
+                unsigned dig;
 		zeros = 0;
 
 		switch (base) {
-		    unsigned dig;
 		case 16:
 		    p = (char *)((c == 'X') ? PL_hexdigit + 16 : PL_hexdigit);
 		    do {
@@ -14677,7 +14677,7 @@ S_find_uninit_var(pTHX_ const OP *const obase, const SV *const uninit_sv,
 	    return varname(gv, '$', 0,
 		    NULL, (I8)obase->op_private, FUV_SUBSCRIPT_ARRAY);
 	}
-	break;
+	NOT_REACHED; /* NOTREACHED */
 
     case OP_EXISTS:
 	o = cUNOPx(obase)->op_first;
@@ -14779,7 +14779,7 @@ S_find_uninit_var(pTHX_ const OP *const obase, const SV *const uninit_sv,
 		? '@' : '%',
 		o->op_targ, NULL, 0, FUV_SUBSCRIPT_WITHIN);
 	}
-	break;
+	NOT_REACHED; /* NOTREACHED */
     }
 
     case OP_AASSIGN:
diff --git a/toke.c b/toke.c
index 4d2254903e..e1a769441f 100644
--- a/toke.c
+++ b/toke.c
@@ -5233,8 +5233,10 @@ Perl_yylex(pTHX)
 	    goto just_a_word_zero_gv;
 	}
 	s++;
+        {
+        OP *attrs;
+
 	switch (PL_expect) {
-	    OP *attrs;
 	case XOPERATOR:
 	    if (!PL_in_my || PL_lex_state != LEX_NORMAL)
 		break;
@@ -5374,6 +5376,7 @@ Perl_yylex(pTHX)
 	    }
 	    TOKEN(COLONATTR);
 	}
+	}
 	if (!PL_lex_allbrackets && PL_lex_fakeeof >= LEX_FAKEEOF_CLOSING) {
 	    s--;
 	    TOKEN(0);
diff --git a/utf8.c b/utf8.c
index f8021996a5..711822609e 100644
--- a/utf8.c
+++ b/utf8.c
@@ -2453,7 +2453,7 @@ Perl__core_swash_init(pTHX_ const char* pkg, const char* name, SV *listsv, I32 m
 		Perl_croak(aTHX_
 			   "Can't find Unicode property definition \"%"SVf"\"",
 			   SVfARG(retval));
-	    Perl_croak(aTHX_ "SWASHNEW didn't return an HV ref");
+                NOT_REACHED; /* NOTREACHED */
 	}
     } /* End of calling the module to find the swash */