https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109580
--- Comment #3 from David Malcolm <dmalcolm at gcc dot gnu.org> ---
The optimized stmt with UNKNOWN_LOCATION is created from:
(gdb) call inform(stmt->location, "stmt in gimple_simplify")
../../src/pr109580.c:10:9: note: stmt in gimple_simplify
10 | err |= dup2(nfd, 0) < 0;
| ^~
here:
(gdb) bt
#0 gimple_set_code (g=<gimple_assign 0x7fffea81c7e8>, code=GIMPLE_ASSIGN) at
../../src/gcc/gimple.cc:112
#1 0x00000000010b2d0f in gimple_init (g=<gimple_assign 0x7fffea81c7e8>,
code=GIMPLE_ASSIGN, num_ops=3) at ../../src/gcc/gimple.cc:131
#2 0x00000000010b2d82 in gimple_alloc (code=GIMPLE_ASSIGN, num_ops=3) at
../../src/gcc/gimple.cc:158
#3 0x00000000010b2de8 in gimple_build_with_ops_stat (code=GIMPLE_ASSIGN,
subcode=98, num_ops=3) at ../../src/gcc/gimple.cc:186
#4 0x00000000010b3c83 in gimple_build_assign_1 (lhs=<ssa_name 0x7fffea81d9d8
37>, subcode=BIT_IOR_EXPR, op1=<ssa_name 0x7fffea64ff78 3>,
op2=<ssa_name 0x7fffea81d0d8 7>, op3=<tree 0x0>) at
../../src/gcc/gimple.cc:469
#5 0x00000000010b3d64 in gimple_build_assign (lhs=<ssa_name 0x7fffea81d9d8
37>, subcode=BIT_IOR_EXPR, op1=<ssa_name 0x7fffea64ff78 3>,
op2=<ssa_name 0x7fffea81d0d8 7>, op3=<tree 0x0>) at
../../src/gcc/gimple.cc:496
#6 0x0000000001c63850 in maybe_push_res_to_seq (res_op=0x7fffffff5980,
seq=0x7fffffffd3d8, res=<ssa_name 0x7fffea81d9d8 37>)
at ../../src/gcc/gimple-match-head.cc:634
#7 0x0000000001d508c9 in gimple_simplify_189 (res_op=0x7fffffffd200,
seq=0x7fffffffd3d8, valueize=0x175579f <fwprop_ssa_val(tree)>,
type=<integer_type 0x7fffea6635e8 int>, captures=0x7fffffff5b30,
bitop=BIT_IOR_EXPR) at gimple-match.cc:52798
#8 0x0000000001e587f2 in gimple_simplify_BIT_IOR_EXPR (res_op=0x7fffffffd200,
seq=0x7fffffffd3d8, valueize=0x175579f <fwprop_ssa_val(tree)>,
code=..., type=<integer_type 0x7fffea6635e8 int>, _p0=<ssa_name
0x7fffea81d120 8>, _p1=<ssa_name 0x7fffea81db88 43>) at gimple-match.cc:115984
#9 0x0000000001fcfaed in gimple_simplify (res_op=0x7fffffffd200,
seq=0x7fffffffd3d8, valueize=0x175579f <fwprop_ssa_val(tree)>, code=...,
type=<integer_type 0x7fffea6635e8 int>, _p0=<ssa_name 0x7fffea81d120 8>,
_p1=<ssa_name 0x7fffea81db88 43>) at gimple-match.cc:211249
#10 0x0000000001c62774 in gimple_resimplify2 (seq=0x7fffffffd3d8,
res_op=0x7fffffffd380, valueize=0x175579f <fwprop_ssa_val(tree)>)
at ../../src/gcc/gimple-match-head.cc:323
#11 0x0000000001c632a2 in gimple_match_op::resimplify (this=0x7fffffffd380,
seq=0x7fffffffd3d8, valueize=0x175579f <fwprop_ssa_val(tree)>)
at ../../src/gcc/gimple-match-head.cc:516
#12 0x0000000001c648ec in gimple_simplify (stmt=<gimple_assign 0x7fffea81c160>,
res_op=0x7fffffffd380, seq=0x7fffffffd3d8,
valueize=0x175579f <fwprop_ssa_val(tree)>, top_valueize=0x175579f
<fwprop_ssa_val(tree)>) at ../../src/gcc/gimple-match-head.cc:1115
#13 0x00000000010dd6dc in fold_stmt_1 (gsi=0x7fffffffd710, inplace=false,
valueize=0x175579f <fwprop_ssa_val(tree)>)
at ../../src/gcc/gimple-fold.cc:6251
#14 0x00000000010dde07 in fold_stmt (gsi=0x7fffffffd710, valueize=0x175579f
<fwprop_ssa_val(tree)>) at ../../src/gcc/gimple-fold.cc:6417
#15 0x0000000001757984 in (anonymous namespace)::pass_forwprop::execute
(this=0x3f79bb0, fun=0x7fffea816000)
at ../../src/gcc/tree-ssa-forwprop.cc:3851
#16 0x0000000001431388 in execute_one_pass (pass=<opt_pass* 0x3f79bb0
"forwprop"(40)>) at ../../src/gcc/passes.cc:2651
#17 0x00000000014317a9 in execute_pass_list_1 (pass=<opt_pass* 0x3f79bb0
"forwprop"(40)>) at ../../src/gcc/passes.cc:2760
#18 0x00000000014317da in execute_pass_list_1 (pass=<opt_pass* 0x3f79a20
"early_optimizations"(37)>) at ../../src/gcc/passes.cc:2761
#19 0x0000000001431839 in execute_pass_list (fn=0x7fffea816000, pass=<opt_pass*
0x3f79820 "fixup_cfg"(34)>) at ../../src/gcc/passes.cc:2771
#20 0x000000000142ef7f in do_per_function_toporder (callback=0x14317f5
<execute_pass_list(function*, opt_pass*)>, data=0x3f79820)
at ../../src/gcc/passes.cc:1780
#21 0x0000000001432567 in execute_ipa_pass_list (pass=<opt_pass* 0x3f797c0
"opt_local_passes"(33)>) at ../../src/gcc/passes.cc:3105
#22 0x0000000000ea7ede in ipa_passes () at ../../src/gcc/cgraphunit.cc:2202
#23 0x0000000000ea8328 in symbol_table::compile (this=0x7fffea648000) at
../../src/gcc/cgraphunit.cc:2323
#24 0x0000000000ea89bb in symbol_table::finalize_compilation_unit
(this=0x7fffea648000) at ../../src/gcc/cgraphunit.cc:2575
#25 0x000000000159fa0f in compile_file () at ../../src/gcc/toplev.cc:471
#26 0x00000000015a33d1 in do_compile (no_backend=false) at
../../src/gcc/toplev.cc:2125
#27 0x00000000015a389b in toplev::main (this=0x7fffffffdd8a, argc=21,
argv=0x7fffffffde98) at ../../src/gcc/toplev.cc:2283
#28 0x0000000002f77c1a in main (argc=21, argv=0x7fffffffde98) at
../../src/gcc/main.cc:39
