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Subject: [Bug bootstrap/55792] [4.8 Regression] Bad memory access with profiledbootstrap and LTO
Date: Wed, 09 Jan 2013 16:11:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55792

--- Comment #19 from H.J. Lu <hjl.tools at gmail dot com> 2013-01-09 16:11:06 UTC ---
The BLOCK tree node is cleared by

(gdb) bt
#0  0x000000336b4882ee in __memset_sse2 () from /lib64/libc.so.6
#1  0x0000000000545fdf in clear_marks ()
    at /export/gnu/import/git/gcc/gcc/ggc-page.c:1815
#2  0x0000000000546621 in ggc_collect ()
    at /export/gnu/import/git/gcc/gcc/ggc-page.c:2086
#3  0x00000000008ad816 in execute_todo (flags=2102)
    at /export/gnu/import/git/gcc/gcc/passes.c:2023
#4  0x00000000008ae175 in execute_one_pass (pass=0x17b9c70)
    at /export/gnu/import/git/gcc/gcc/passes.c:2349
#5  0x00000000008ae2da in execute_pass_list (pass=0x17b9c70)
    at /export/gnu/import/git/gcc/gcc/passes.c:2383
#6  0x00000000008ae30b in execute_pass_list (
    pass=0x16d07e0 <pass_all_optimizations>)
    at /export/gnu/import/git/gcc/gcc/passes.c:2384
#7  0x00000000005da366 in expand_function (node=0x7ffff16f5378)
    at /export/gnu/import/git/gcc/gcc/cgraphunit.c:1641
#8  0x00000000005da821 in expand_all_functions ()
    at /export/gnu/import/git/gcc/gcc/cgraphunit.c:1745
#9  0x00000000005db2ab in compile ()
    at /export/gnu/import/git/gcc/gcc/cgraphunit.c:2043
#10 0x000000000053c60a in lto_main ()
    at /export/gnu/import/git/gcc/gcc/lto/lto.c:3390
#11 0x0000000000999401 in compile_file ()
---Type <return> to continue, or q <return> to quit---
    at /export/gnu/import/git/gcc/gcc/toplev.c:545
#12 0x000000000099b3e4 in do_compile ()
    at /export/gnu/import/git/gcc/gcc/toplev.c:1878
#13 0x000000000099b54f in toplev_main (argc=28, argv=0x7fffffffdc78)
    at /export/gnu/import/git/gcc/gcc/toplev.c:1954
#14 0x0000000000fff958 in main (argc=28, argv=0x7fffffffdc78)
    at /export/gnu/import/git/gcc/gcc/main.c:36
(gdb)

When we remap a block:
static void
remap_block (tree *block, copy_body_data *id)
{
  tree old_block;
  tree new_block;

  /* Make the new block.  */
  old_block = *block;
  new_block = make_node (BLOCK);
  TREE_USED (new_block) = TREE_USED (old_block);
  BLOCK_ABSTRACT_ORIGIN (new_block) = old_block;
  BLOCK_SOURCE_LOCATION (new_block) = BLOCK_SOURCE_LOCATION (old_block);
  BLOCK_NONLOCALIZED_VARS (new_block)
    = vec_safe_copy (BLOCK_NONLOCALIZED_VARS (old_block));
  *block = new_block;

  /* Remap its variables.  */
  BLOCK_VARS (new_block) = remap_decls (BLOCK_VARS (old_block),
                                        &BLOCK_NONLOCALIZED_VARS (new_block),
                                        id);

we didn't register it with GC root.