Bug 36635 - [4.4 Regression] cc1 segfault from svn 137122
Summary: [4.4 Regression] cc1 segfault from svn 137122
Alias: None
Product: gcc
Classification: Unclassified
Component: target (show other bugs)
Version: 4.4.0
: P1 normal
Target Milestone: 4.4.0
Assignee: Jakub Jelinek
Keywords: ice-on-valid-code
Depends on:
Blocks: 33424 37290
  Show dependency treegraph
Reported: 2008-06-25 22:01 UTC by John Regehr
Modified: 2008-10-08 08:16 UTC (History)
3 users (show)

See Also:
Host: i686-pc-linux-gnu
Target: i686-pc-linux-gnu
Build: i686-pc-linux-gnu
Known to work:
Known to fail:
Last reconfirmed: 2008-10-07 16:16:48

Patch for cse.c (584 bytes, patch)
2008-07-05 07:57 UTC, Chung-Lin Tang
Details | Diff

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Description John Regehr 2008-06-25 22:01:37 UTC
[regehr@babel tmp31]$ current-gcc -O3 small.c
current-gcc: Internal error: Segmentation fault (program cc1)
Please submit a full bug report.
See <http://gcc.gnu.org/bugs.html> for instructions.

[regehr@babel tmp31]$ current-gcc -v
Using built-in specs.
Target: i686-pc-linux-gnu
Configured with: ../configure --program-prefix=current- --enable-languages=c,c++ --prefix=/home/regehr
Thread model: posix
gcc version 4.4.0 20080625 (experimental) (GCC) 

[regehr@babel tmp31]$ cat small.c

typedef int int32_t;
typedef unsigned char uint8_t;
typedef unsigned int uint32_t;
static inline unsigned int
lshift_u_u (unsigned int left, unsigned int right)
  if ((right >= sizeof (unsigned int))
      || (left > ((2147483647 * 2U + 1U) >> right)))
    return left;
static inline unsigned long int
mod_rhs (const long int rhs)
  return rhs;
static inline unsigned long int
div_rhs (const long int rhs)
  return rhs;

uint32_t g_22;
func_53 (uint32_t p_54, uint32_t p_55, uint32_t p_56, uint8_t p_57)
  int32_t l_58 = 0xB8BF5144L;
  for (0; 1; p_56 -= 0)
      uint32_t l_59 = -1L;
      if (((lshift_u_u ((g_22 / div_rhs (l_58)), (1 % mod_rhs (l_59))))))
        return 1;
      for (l_59 = 0; (l_59 <= -20); l_59 += 1)
Comment 1 Richard Biener 2008-06-26 10:25:28 UTC
Confirmed.  We endlessly recurse in cse_cc_succs.
Comment 2 Chung-Lin Tang 2008-07-05 07:57:38 UTC
Created attachment 15859 [details]
Patch for cse.c

I have looked at the debug dumps for the testcase.
This seems like a very rare case:

1. -O3 turns on the loop unswitching pass (-funswitch-loops),
   which transforms the function into two loops guarded by a
   conditional branch from a header block.

2. During cse2 (the immediately next pass),
   cse.c:cse_main() transforms that conditional branch into a jump,
   cutting off the connection to one of the loops.

3. The cut off loop becomes segregated from the other basic blocks,
   and becomes a circular loop, with a single edge acting as both the
   entry and latch edge.

4. This cut off loop still contains control flow, and sets CC within.
   cse.c:cse_condition_reg() calls the recursive cse_cc_succs() to delete
   redundant CC setters on this circular loop.

5. cse.c:cse_cc_succs() uses the "single predecessor edge" condition as the
   stopping control flow test, which in this case of a single edge circular
   loop (a "ring" like control flow structure), fails to properly stop the
   recursion. cse_cc_succs() then blows up the stack and segfaults.

The proposed fix is to record visited basic blocks during the
recursive traversal, see the enclosed patch.
Comment 3 Jakub Jelinek 2008-10-07 14:57:59 UTC
This one isn't reproducible for me on the trunk.
Comment 4 Jakub Jelinek 2008-10-07 16:16:48 UTC
I've reproduced PR37341 though.  And I believe your patch is an overkill, as
cse_cc_succs only recurses if edge destination has a single predecessor.
So IMHO you don't need to keep a bitmap of visited blocks, as the only way
to reach endless recursion is if you eventually reach the original bb cse_condition_code_reg called cse_cc_succs with, as if there is a smaller loop there would be some bb with more than one predecessor.

To fix this, we can either add an extra argument to cse_cc_succs (the original bb) and bail if e->dest is equal to orig_bb; IMHO this is the cheapest variant),
or we could call find_unreachable_blocks () if tem > 0 before cse_condition_code_reg and disregard (bb->flags & BB_REACHABLE) == 0 bb's (or delete_unreachable_blocks ()).
Comment 5 Jakub Jelinek 2008-10-08 08:13:54 UTC
Subject: Bug 36635

Author: jakub
Date: Wed Oct  8 08:12:25 2008
New Revision: 140966

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=140966
	PR target/36635
	PR target/37290
	PR rtl-optimization/37341
	* cse.c (cse_cc_succs): Add ORIG_BB argument, don't follow edges
	to ORIG_BB, pass through ORIG_BB recursively.
	(cse_condition_code_reg): Adjust caller.

	* gcc.c-torture/compile/pr37341.c: New test.


Comment 6 Jakub Jelinek 2008-10-08 08:16:40 UTC