[Bug tree-optimization/50385] New: missed-optimization: jump to __builtin_unreachable() not removed

[Bug tree-optimization/50385] New: missed-optimization: jump to __builtin_unreachable() not removed

[wouter.vermaelen at scarlet dot be]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50385

             Bug #: 50385
           Summary: missed-optimization: jump to __builtin_unreachable()
                    not removed
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: wouter.vermaelen@scarlet.be


I'm not sure, but this issue might be the same as bug 49054 (if so, feel free
to delete this one).


#include <vector>

struct S { int a, b; };
std::vector<S> v;

int search_1(int a) {
    for (auto it = v.begin(); /**/; ++it)
        if (it->a == a) return it->b;
}
int search_2(int a) {
    for (auto& e : v)
        if (e.a == a) return e.b;
    __builtin_unreachable();
}


I expected to see the same generated code for both functions. Instead the 2nd
one still contains some useless comparisons and jumps past the end of the
function. Since such a (conditional) jump is anyway undefined behavior it can
as well be removed (including the instructions required to calculate the
condition).

Tested with SVN revision 178775 (20110912) on Linux x86_64.

[Bug middle-end/50385] missed-optimization: jump to __builtin_unreachable() not removed

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50385

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011-11-11
          Component|tree-optimization           |middle-end
     Ever Confirmed|0                           |1

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> 2011-11-11 00:39:55 UTC ---
Confirmed with a much simpler testcase:
int
f (int i)
{
  if (i <= 1)
    return 1;
  __builtin_unreachable();
}
--- CUT ---
I found this while adding a basic block reordering pass to the tree level and I
got a failure with builtin-unreachable-2.c .

[Bug middle-end/50385] missed-optimization: jump to __builtin_unreachable() not removed

[glisse at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50385

--- Comment #2 from Marc Glisse <glisse at gcc dot gnu.org> ---
This seems to work on current trunk. Can you confirm, and if so close the PR?
(well, we may want to add the testcases)

[Bug middle-end/50385] missed-optimization: jump to __builtin_unreachable() not removed

[law at redhat dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=50385

Jeffrey A. Law <law at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |law at redhat dot com
         Resolution|---                         |FIXED

--- Comment #3 from Jeffrey A. Law <law at redhat dot com> ---
Trunk produces the desired code.