https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111851
Bug ID: 111851
Summary: f951: Segmentation fault at gfc_delete_symtree
Product: gcc
Version: 13.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: fortran
Assignee: unassigned at gcc dot gnu.org
Reporter: canu7 at yahoo dot es
Target Milestone: ---
I'm using the following gfortran version on Arch Linux:
```
Using built-in specs.
COLLECT_GCC=gfortran
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-pc-linux-gnu/13.2.1/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /build/gcc/src/gcc/configure
--enable-languages=ada,c,c++,d,fortran,go,lto,objc,obj-c++ --enable-bootstrap
--prefix=/usr --libdir=/usr/lib --libexecdir=/usr/lib --mandir=/usr/share/man
--infodir=/usr/share/info --with-bugurl=https://bugs.archlinux.org/
--with-build-config=bootstrap-lto --with-linker-hash-style=gnu
--with-system-zlib --enable-__cxa_atexit --enable-cet=auto
--enable-checking=release --enable-clocale=gnu --enable-default-pie
--enable-default-ssp --enable-gnu-indirect-function --enable-gnu-unique-object
--enable-libstdcxx-backtrace --enable-link-serialization=1
--enable-linker-build-id --enable-lto --enable-multilib --enable-plugin
--enable-shared --enable-threads=posix --disable-libssp --disable-libstdcxx-pch
--disable-werror
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 13.2.1 20230801 (GCC)
```
Here is the reduced code that causes the segmentation fault:
```Fortran
SELECT TYPE (rvec2ASSOCIATE(
```
This is the result of executing it directly with `f951`:
```
/usr/lib/gcc/x86_64-pc-linux-gnu/13.2.1/f951 test.f90
f951: internal compiler error: Segmentation fault
0x1a0e9c4 internal_error(char const*, ...)
???:0
0x7be65c gfc_delete_symtree(gfc_symtree**, char const*)
???:0
0x7c3f84 gfc_restore_last_undo_checkpoint()
???:0
0x793804 gfc_parse_file()
???:0
Please submit a full bug report, with preprocessed source (by using
-freport-bug).
Please include the complete backtrace with any bug report.
See <https://bugs.archlinux.org/> for instructions.
```
This is the gdb backtrace on the segmentation fault:
```
#0 0x00000000006b193f in delete_root (t=0x2b60890) at
/usr/src/debug/gcc/gcc/gcc/fortran/bbt.cc:150
#1 0x00000000007be65d in delete_treap (compare=0x79c650
<compare_symtree(void*, void*)>, t=0x2b60890, old=0x7fffffffdd90)
at /usr/src/debug/gcc/gcc/gcc/fortran/bbt.cc:185
#2 gfc_delete_bbt (compare=0x79c650 <compare_symtree(void*, void*)>,
old=0x7fffffffdd90, root=0x2bbfce0) at
/usr/src/debug/gcc/gcc/gcc/fortran/bbt.cc:197
#3 gfc_delete_symtree (root=0x2bbfce0, name=<optimized out>) at
/usr/src/debug/gcc/gcc/gcc/fortran/symbol.cc:2969
#4 0x00000000007c3f85 in gfc_restore_last_undo_checkpoint () at
/usr/src/debug/gcc/gcc/gcc/fortran/symbol.cc:3714
#5 0x000000000076b342 in gfc_undo_symbols () at
/usr/src/debug/gcc/gcc/gcc/fortran/symbol.cc:3747
#6 reject_statement () at /usr/src/debug/gcc/gcc/gcc/fortran/parse.cc:2905
#7 0x00000000007638ae in match_word (old_locus=0x7fffffffdf00, subr=0x73eb20
<gfc_match_select_type()>, str=0x0) at
/usr/src/debug/gcc/gcc/gcc/fortran/parse.cc:72
#8 decode_statement () at /usr/src/debug/gcc/gcc/gcc/fortran/parse.cc:430
#9 0x000000000076f8c2 in next_free () at
/usr/src/debug/gcc/gcc/gcc/fortran/parse.cc:1406
#10 next_statement () at /usr/src/debug/gcc/gcc/gcc/fortran/parse.cc:1638
#11 0x0000000000793805 in gfc_parse_file () at
/usr/src/debug/gcc/gcc/gcc/fortran/parse.cc:6789
#12 0x00000000007ced05 in gfc_be_parse_file () at
/usr/src/debug/gcc/gcc/gcc/fortran/f95-lang.cc:229
#13 0x0000000000d630c1 in compile_file () at
/usr/src/debug/gcc/gcc/gcc/toplev.cc:444
#14 0x00000000006ad7fb in do_compile (no_backend=false) at
/usr/src/debug/gcc/gcc/gcc/toplev.cc:2125
#15 toplev::main (this=<optimized out>, argc=<optimized out>, argv=<optimized
out>) at /usr/src/debug/gcc/gcc/gcc/toplev.cc:2277
#16 0x00000000006ae0e2 in main (argc=<optimized out>, argv=<optimized out>) at
/usr/src/debug/gcc/gcc/gcc/main.cc:39
```
And this is the line and the values that I think causes the problem:
```
0x00000000006b193f in delete_root (t=0x2b60890) at
/usr/src/debug/gcc/gcc/gcc/fortran/bbt.cc:150
Downloading source file /usr/src/debug/gcc/gcc/gcc/fortran/bbt.cc
150 if (t->left->priority > t->right->priority)
(gdb) p t
$1 = (gfc_bbt *) 0x2b60890
(gdb) p t->left
$2 = (gfc_treap *) 0xf1
(gdb) p t->right
$3 = (gfc_treap *) 0x2bba400
```
And finally, here is a Compiler Explorer link reproducing the bug:
https://godbolt.org/z/z7W35ra4s
Hope is enough information to pin-point the problem.
