fallthrough should not execute case expression

[alexlamsl]

Also enable switch statement fuzzing.

fixes #1680

[alexlamsl]

//=============================================================
// !!!!!! Failed...
// original code
//
var a = 100, b = 10;
function f21(){var Math79 = (a++), foo80 = ([,0].length === 2);{var brake81 = 5; while (((0 === 1 ? a : b)^new function(){
(b ^= a)
return Math;
}) && --brake81 > 0){{var brake83 = 5; do {;} while (((0 === 1 ? a : b)) && --brake83 > 0);}{!true}{!true}if ((typeof NaN93 != "number"))switch (null) { case (function a95(){switch ((0 === 1 ? a : b)) { case (a--):

 break;
case void function let97(){{;}{;}if (25. ); else ;}:
{var brake103 = 5; while (((22)) && --brake103 > 0)switch (({})) { case [,0][1]:
;
 break;
case undefined:
;
 break;
case [,0][1]:
;
 break;
case undefined:
;
 break;
}}
 break;
case (0 === 1 ? a : b):
;var arguments;
 break;
case (a--):
{}
 break;
}return;})()?((--(b))):((b !== a)):

 break;
case (a++):
;
 break;
case (--b):

 break;
case (typeof undefined110 == "unknown"):
;
 break;
}}}}
f21();

console.log(a, b);


//-------------------------------------------------------------
// original code (beautify'd)
//
var a = 100, b = 10;

function f21() {
    var Math79 = a++, foo80 = [ , 0 ].length === 2;
    {
        var brake81 = 5;
        while ((0 === 1 ? a : b) ^ new function() {
            b ^= a;
            return Math;
        }() && --brake81 > 0) {
            {
                var brake83 = 5;
                do {
                } while ((0 === 1 ? a : b) && --brake83 > 0);
            }
            {
                !true;
            }
            {
                !true;
            }
            if (typeof NaN93 != "number") {
                switch (null) {
                  case function a95() {
                        switch (0 === 1 ? a : b) {
                          case a--:
                            break;

                          case void function let97() {
                                {
                                }
                                {
                                }
                                if (25) {} else {}
                            }:
                            {
                                var brake103 = 5;
                                while (22 && --brake103 > 0) {
                                    switch ({}) {
                                      case [ , 0 ][1]:
                                        ;
                                        break;

                                      case undefined:
                                        ;
                                        break;

                                      case [ , 0 ][1]:
                                        ;
                                        break;

                                      case undefined:
                                        ;
                                        break;
                                    }
                                }
                            }
                            break;

                          case 0 === 1 ? a : b:
                            ;
                            var arguments;
                            break;

                          case a--:
                            {}
                            break;
                        }
                        return;
                    }() ? --b : b !== a:
                    break;

                  case a++:
                    ;
                    break;

                  case --b:
                    break;

                  case typeof undefined110 == "unknown":
                    ;
                    break;
                }
            }
        }
    }
}

f21();

console.log(a, b);


//-------------------------------------------------------------
// uglified code
//
function f21(){for(var e=(a++,[,0].length,5);b^new function(){return b^=a,Math}&&--e>0;){var c=5;do{}while(b&&--c>0);if("number"!=typeof NaN93)switch(null){case function(){switch(b){case a--:case a--:break;case void 0:for(var e=5;--e>0;)switch({}){case[,0][1]:case void 0:case[,0][1]:}}}()?--b:b!==a:case a++:case--b:case"unknown"==typeof undefined110:}}}var a=100,b=10;f21(),console.log(a,b);


original result:
101 111

beautified result:
101 111

uglified result:
97 107

!!!!!! Failed...

[kzc]

Was that a new failure with this PR?

[alexlamsl]

Nope - just a different bug after re-enabling switch in test/ufuzz.js. It's an easy fix, so lump it over here.

I'll continue to catch those low hanging fruits, then commit this PR.

[kzc]

That fuzzer is crazy useful.

[kzc]

When a side effect is found in any case condition at all shouldn't the optimization of the switch be abandoned?

[alexlamsl]

Unlike previously, we are not eliminating the switch block completely or give up.

We drop definitely unreachable cases, de-duplicate others. Only then do we look at the switch block to see if it contains only one case which is definitely reachable.

If that's the case, then we ouput an AST_BlockStatement, otherwise we return the (now optimised) AST_Switch.

[kzc]

Good thing you have a fuzzer. There's a lot things that can potentially go wrong.

[alexlamsl]

Yup - without that I wouldn't have started #1677 at all.