https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118790
--- Comment #26 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
So, seems id_string is mentioned in BLOCK_VARS of the ec_meminfo BLOCK:
BLOCK #0 [written]
SUPERCONTEXT: ec_meminfo
SUBBLOCKS: BLOCK #109 [written] BLOCK #166 [written] BLOCK #167 [written]
BLOCK #168 [written] BLOCK #169 [written]
VARS: rnsort check_error prt_data slash_proc i nproc error clpfx .id_string
id_string line node k n18 smallpage nnuma j bucket hugepage memfree cached
clstr coreids icoreid iorank ubound.30 irecv_status itag lastnode llfirst_time
llnocomm maxth mpi_byte mpi_comm_world mpi_integer4 myproc myth rn i
even before any unused var removals.
While id_string.55 is created in the gimplifier, gimplify_vla_decl on
id_string:
1981 addr = create_tmp_var (ptr_type, get_name (decl));
1982 DECL_IGNORED_P (addr) = 0;
1983 t = build_fold_indirect_ref (addr);
1984 TREE_THIS_NOTRAP (t) = 1;
1985 SET_DECL_VALUE_EXPR (decl, t);
and so it is added to cfun->local_decls.
Now, during remove_unused_locals, neither id_string nor id_string.55 are
actually marked as used, they are not used in the IL anymore.
But id_string is preserved in BLOCK_VARS due to remove_unused_scope_block_p:
/* If a decl has a value expr, we need to instantiate it
regardless of debug info generation, to avoid codegen
differences in memory overlap tests. update_equiv_regs() may
indirectly call validate_equiv_mem() to test whether a
SET_DEST overlaps with others, and if the value expr changes
by virtual register instantiation, we may get end up with
different results. */
else if (VAR_P (*t) && DECL_HAS_VALUE_EXPR_P (*t))
unused = false;
(added in r0-93860).
But nothing does that something similar for VAR_DECLs with
DECL_HAS_VALUE_EXPR_P in local_decls.
So, shall we always preserve all the DECL_HAS_VALUE_EXPR_P local_decls?
Or shall we mark the DECL_HAS_VALUE_EXPR_P VAR_DECLs and their DECL_VALUE_EXPRs
as used?
Something else?
