[cfe-dev] SwitchStmt bug?

[Per Viberg]

thanks guys for the quick reply,

yeah, I suspected something like that. The only thing I was surprised about was that there is a Stmt at all inside a switch "label". I mean, if they are just like goto labels, then no statement at all would seem more intuitive.

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Per Viberg Senior Engineer
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________________________________
Från: Jordan Rose [jordan_rose at apple.com]
Skickat: den 10 mars 2014 17:20
Till: Per Viberg
Cc: cfe-dev Developers; Tom Honermann
Ämne: Re: [cfe-dev] SwitchStmt bug?


On Mar 10, 2014, at 7:49 , Tom Honermann <thonermann at coverity.com<mailto:thonermann at coverity.com>> wrote:

On 03/10/2014 10:23 AM, Per Viberg wrote:

Hi all,

I was inspecting the AST dump of this switch:

void test_switch(int t) {
  switch(t)
  {
  case 1:
    y = 11;
  case 2:
    y = 9;
    x = 12;
    break;
  default:
    break;
  }
}

and I got something I didn't expect. The second CaseStmt does only
contain the first statement that is under it's label. The "x=12;" gets
its own Stmt outside the CaseStmt but inside the CompoundStmt inside the
SwitchStmt. I would anticipate that all statements under a label either
are: inside the CaseStmt or: outside but inside the CompoundStmt. Any
reason for this?.

This is expected.  Case statements have just one sub statement.

More generally, case statements are just labels, and have the same basic rules as regular old goto labels. Having case statements "just" be labels is what allows things like Duff's Device<http://en.wikipedia.org/wiki/Duff's_device> in C:

switch(count % 8) {
case 0: do { *to = *from++;
case 7: *to = *from++;
case 6: *to = *from++;
case 5: *to = *from++;
case 4: *to = *from++;
case 3: *to = *from++;
case 2: *to = *from++;
case 1: *to = *from++;
} while(--n > 0);
}

This is the opposite situation, really, because here we need cases inside the loop that's inside the switch. But once you're supporting this, the representation as a simple label is just easier to work with.

Jordan

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