tree-ssa-live: Fix .DEFERRED_INIT handling [PR122184]

remove_unused_locals ignores clobbers in the initial phase (and
some debug stmts) and this has been copied for .DEFERRED_INIT
as well:
          if (gimple_clobber_p (stmt))
            {
              have_local_clobbers = true;
              continue;
            }

          if (gimple_call_internal_p (stmt, IFN_DEFERRED_INIT))
            {
              have_local_clobbers = true;
              continue;
            }
This is so that the second phase can then drop clobbers that
clobber unused local vars and ditto for .DEFERRED_INIT.
Except, for clobbers it does
                /* Remove clobbers referencing unused vars, or clobbers
                   with MEM_REF lhs referencing uninitialized pointers.  */
                if ((VAR_P (base) && !is_used_p (base))
                    || (TREE_CODE (lhs) == MEM_REF
                        && TREE_CODE (TREE_OPERAND (lhs, 0)) == SSA_NAME
                        && SSA_NAME_IS_DEFAULT_DEF (TREE_OPERAND (lhs, 0))
                        && (TREE_CODE (SSA_NAME_VAR (TREE_OPERAND (lhs, 0)))
                            != PARM_DECL)))
so handles both the var = {CLOBBER}; case where var is unused local,
or *SSA_NAME = {CLOBBER} where SSA_NAME is default definition of
non-PARM_DECL, but for .DEFERRED_INIT it doesn't:
                if (DECL_P (base) && !is_used_p (base))
On the following case, we have *SSA_NAME(D) = .DEFERRED_INIT (...);
and because of the former we don't mark the SSA_NAME as used and
because of the latter we keep the .DEFERRED_INIT call, so the SSA_NAME
is freed and later on we ICE because the SSA_NAME in the freelist doesn't
have SSA_NAME_DEF_STMT.

The following patch fixes it by handling .DEFERRED_INIT like clobbers
and dropping them also when it has a MEM_REF with default definition
of SSA_NAME for non-PARM_DECL on the lhs.

2025-11-19  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/122184
	* tree-ssa-live.cc (remove_unused_locals): Drop .DEFERRED_INIT
	calls with MEM_REF lhs based on uninitialized SSA_NAME.

	* g++.dg/opt/pr122184-1.C: New test.
	* g++.dg/opt/pr122184-2.C: New test.

0 files changed, 0 insertions, 0 deletions