Re: c/8828: gcc reports some code is unreachable when it is not

["Christian Ehrhardt" <ehrhardt@mathematik.uni-ulm.de>]

The following reply was made to PR c/8828; it has been noted by GNATS.

From: "Christian Ehrhardt" <ehrhardt@mathematik.uni-ulm.de>
To: Rolf Campbell <rcampbell@tropicnetworks.com>
Cc: reichelt@igpm.rwth-aachen.de, gcc-bugs@gcc.gnu.org, gcc-prs@gcc.gnu.org,
  nobody@gcc.gnu.org, gcc-gnats@gcc.gnu.org
Subject: Re: c/8828: gcc reports some code is unreachable when it is not
Date: Sat, 7 Dec 2002 01:58:19 +0100

 On Fri, Dec 06, 2002 at 11:22:32AM -0500, Rolf Campbell wrote:
 > But, this was compiled WITHOUT optimizations (gcc -Wunreachable-code -c
 > a.c), so there should be no removal of superfluous code, or folding of
 > break statements.
 
 Even without optimization it is possible that some code is unused
 and removed. In this particular case the following case statement
 
 switch (i) {
 case 0:
    for (; i<2; i++)
       x++
    break;
 case 1:
    x++;break;
 }
 
 Is rewritten to look like this (even without optimization this is allowed):
 switch (i) {
 case 0:
 startfor:
    if (i>=2)
       goto caseend;
    x++; i++;
    goto startfor;
    break;
 case 1:
    x++;break;
 }
 caseend:
 
 which makes the first break statement unreachable. This is completly
 legal and the compiler is even right in some sense that the break
 statement is unreachable. Others should decide if this is actually a
 bug but the warning is off by default for a reason.
 
     regards   Christian
 
 -- 
 THAT'S ALL FOLKS!