Re: optimization/10862: [tree-ssa] Segfault for (essentially) empty function

The following reply was made to PR optimization/10862; it has been noted by GNATS.

From: [email protected]
To: [email protected]
Cc: [email protected], [email protected]
Subject: Re: optimization/10862: [tree-ssa] Segfault for (essentially) empty 
 function
Date: Mon, 19 May 2003 12:12:35 -0600

 In message <[email protected]>, [email protected]
  writes:
  >
  >>Number:         10862
  >>Category:       optimization
  >>Synopsis:       [tree-ssa] Segfault for (essentially) empty function
  >>Confidential:   no
  >>Severity:       serious
  >>Priority:       medium
  >>Responsible:    unassigned
  >>State:          open
  >>Class:          sw-bug
  >>Submitter-Id:   net
  >>Arrival-Date:   Mon May 19 14:46:01 UTC 2003
  >>Closed-Date:
  >>Last-Modified:
  >>Originator:     Wolfgang Bangerth
  >>Release:        unknown-1.0
  >>Organization:
  >>Environment:
  >
  >>Description:
  >This one's rather funny (and was much simpler to reduce).
  >We ICE on a function that's essentially empty:
  >---------------------------------------template <int N> void foo () {
  >  int i;
  >  switch (i) {
  >    case 1:
  >          switch (N) {}
  >    default: ;
  >  }
  >}
  >
  >template void foo<1> ();
  >---------------------------
  >
  >g/x> /home/bangerth/bin/gcc-3.4-tree-ssa/bin/c++ -O2 -c a.cc
  >a.cc: In function `void foo() [with int N = 1]':
  >a.cc:10:   instantiated from here
  >a.cc:6: internal compiler error: Segmentation fault
  >Please submit a full bug report,
  >with preprocessed source if appropriate.
  >See <URL:http://gcc.gnu.org/bugs.html> for instructions.
 This patch ought to fix this problem.
 
 	* tree-ssa-dce.c (remove_conditional): If the conditional's block
 	has no post dominator in the CFG, then wire it to the exit node.
 	Avoid unnecessary check of bb->succ.
 
 Index: tree-ssa-dce.c
 ===================================================================
 RCS file: /cvs/gcc/gcc/gcc/Attic/tree-ssa-dce.c,v
 retrieving revision 1.1.2.37
 diff -c -3 -p -r1.1.2.37 tree-ssa-dce.c
 *** tree-ssa-dce.c	16 May 2003 18:09:19 -0000	1.1.2.37
 --- tree-ssa-dce.c	19 May 2003 16:50:25 -0000
 *************** remove_conditional (basic_block bb)
 *** 627,632 ****
 --- 627,637 ----
     if (bb->succ)
       return;
   
 +   /* If there is no post dominator, then this block is going to the
 +      exit node.  */
 +   if (pdom_bb == NULL)
 +     pdom_bb = EXIT_BLOCK_PTR;
 + 
     /* If the post dominator has any PHI nodes in it at all, the 
        conditional has been marked as necessary. This means no PHI
        node updating is required. If there are any PHI nodes, its a bug
 *************** remove_conditional (basic_block bb)
 *** 642,647 ****
   #endif
   
     /* Add an edge to BB's post dominator.  */
 !   if (bb->succ == NULL)
 !     make_edge (bb, pdom_bb,  EDGE_FALLTHRU);
   }
 --- 647,651 ----
   #endif
   
     /* Add an edge to BB's post dominator.  */
 !   make_edge (bb, pdom_bb,  EDGE_FALLTHRU);
   }