f33b9c40b9
DCE tries to delete dead stores to local data and also tries to insert
debug binds for simple cases:
/* If this is a store into a variable that is being optimized away,
add a debug bind stmt if possible. */
if (MAY_HAVE_DEBUG_BIND_STMTS
&& gimple_assign_single_p (stmt)
&& is_gimple_val (gimple_assign_rhs1 (stmt)))
{
tree lhs = gimple_assign_lhs (stmt);
if ((VAR_P (lhs) || TREE_CODE (lhs) == PARM_DECL)
&& !DECL_IGNORED_P (lhs)
&& is_gimple_reg_type (TREE_TYPE (lhs))
&& !is_global_var (lhs)
&& !DECL_HAS_VALUE_EXPR_P (lhs))
{
tree rhs = gimple_assign_rhs1 (stmt);
gdebug *note
= gimple_build_debug_bind (lhs, unshare_expr (rhs), stmt);
gsi_insert_after (i, note, GSI_SAME_STMT);
}
}
But this doesn't help for things like "print *ptr" when ptr points
to the local variable (tests Og-dce-1.c and Og-dce-2.c). It can
also introduce wrong debug info for earlier references (second test
in Og-dce-3.c) or make earlier references unavailable (first test
in Og-dce-3.c).
So for -Og I think it'd be better not to delete any stmts with
vdefs for now. This also means that we can avoid the potentially
expensive vop walks (which already have a cut-off, but still).
The patch also fixes the Og failures in gcc.dg/guality/pr54970.c
(PR 86638).
2019-07-29 Richard Sandiford <richard.sandiford@arm.com>
gcc/
PR debug/86638
* tree-ssa-dce.c (keep_all_vdefs_p): New function.
(mark_stmt_if_obviously_necessary): Mark all stmts with vdefs as
necessary if keep_all_vdefs_p is true.
(mark_aliased_reaching_defs_necessary): Add a gcc_checking_assert
that keep_all_vdefs_p is false.
(mark_all_reaching_defs_necessary): Likewise.
(propagate_necessity): Skip the vuse scan if keep_all_vdefs_p is true.
gcc/testsuite/
* c-c++-common/guality/Og-dce-1.c: New test.
* c-c++-common/guality/Og-dce-2.c: Likewise.
* c-c++-common/guality/Og-dce-3.c: Likewise.
From-SVN: r273872
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