[Bug tree-optimization/97159] New: segfault in modref_may_conflict

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97159

            Bug ID: 97159
           Summary: segfault in modref_may_conflict
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vries at gcc dot gnu.org
  Target Milestone: ---

With a build of commit 48b0c1250a5c7d72be6b3fbbb1117d1cce43daee (Date: Mon Sep
21 12:46:00 2020 +0200) for x86_64-linux with nvptx accelerator, we run into:
...
FAIL: libgomp.fortran/examples-4/declare_target-1.f90   -O1  (internal compiler
error)
...

In more detail:
...
during GIMPLE pass: dse^M
/home/vries/oacc/trunk/source-gcc/libgomp/testsuite/libgomp.fortran/examples-4/declare_target-1.f90:
In function 'fib':^M
/home/vries/oacc/trunk/source-gcc/libgomp/testsuite/libgomp.fortran/examples-4/declare_target-1.f90:6:
internal compiler error: Segmentation fault^M
0x1133447 crash_signal^M
        /home/vries/oacc/trunk/source-gcc/gcc/toplev.c:327^M
0x12b1a69 modref_may_conflict^M
        /home/vries/oacc/trunk/source-gcc/gcc/tree-ssa-alias.c:2433^M
0x12b1da0 ref_maybe_used_by_call_p_1^M
        /home/vries/oacc/trunk/source-gcc/gcc/tree-ssa-alias.c:2513^M
0x12b2af9 ref_maybe_used_by_call_p^M
        /home/vries/oacc/trunk/source-gcc/gcc/tree-ssa-alias.c:2832^M
0x12b2c2f ref_maybe_used_by_stmt_p(gimple*, ao_ref*, bool)^M
        /home/vries/oacc/trunk/source-gcc/gcc/tree-ssa-alias.c:2864^M
0x12e8b6f dse_classify_store(ao_ref*, gimple*, bool, simple_bitmap_def*, bool*,
tree_node*)^M
        /home/vries/oacc/trunk/source-gcc/gcc/tree-ssa-dse.c:831^M
0x12e9817 dse_dom_walker::dse_optimize_stmt(gimple_stmt_iterator*)^M
        /home/vries/oacc/trunk/source-gcc/gcc/tree-ssa-dse.c:1151^M
0x12e9947 dse_dom_walker::before_dom_children(basic_block_def*)^M
        /home/vries/oacc/trunk/source-gcc/gcc/tree-ssa-dse.c:1183^M
0x1bef976 dom_walker::walk(basic_block_def*)^M
        /home/vries/oacc/trunk/source-gcc/gcc/domwalk.c:309^M
0x12e9ac0 execute^M
        /home/vries/oacc/trunk/source-gcc/gcc/tree-ssa-dse.c:1237^M
...