Hi! The following testcase FAILs, because gimplify_body adds a GIMPLE_NOP only when there are no statements in the function and with -g there is a DEBUG_BEGIN_STMT, so it doesn't add it and due to -fno-tree-dce that never gets removed afterwards. Similarly, if the body seq after gimplification contains some DEBUG_BEGIN_STMTs plus a single gbind, then we could behave differently between -g0 and -g, by using that gbind as the body in the -g0 case and not in the -g case. This patch fixes that by ignoring DEBUG_BEGIN_STMTs (other debug stmts can't appear at this point yet thankfully) during decisions and if we pick the single gbind and there are DEBUG_BEGIN_STMTs next to it, it moves them into the gbind. While debugging this, I found also a bug in the gimple_seq_last_nondebug_stmt function, for a seq that has a single non-DEBUG_BEGIN_STMT statement followed by one or more DEBUG_BEGIN_STMTs it would return NULL rather than the first statement.
Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk? 2020-03-26 Jakub Jelinek <ja...@redhat.com> PR debug/94281 * gimple.h (gimple_seq_first_nondebug_stmt): New function. (gimple_seq_last_nondebug_stmt): Don't return NULL if seq contains a single non-debug stmt followed by one or more debug stmts. * gimplify.c (gimplify_body): Use gimple_seq_first_nondebug_stmt instead of gimple_seq_first_stmt, use gimple_seq_first_nondebug_stmt and gimple_seq_last_nondebug_stmt instead of gimple_seq_first and gimple_seq_last to check if outer_stmt gbind could be reused and if yes and it is surrounded by any debug stmts, move them into the gbind body. * g++.dg/debug/pr94281.C: New test. --- gcc/gimple.h.jj 2020-03-25 14:34:07.696199561 +0100 +++ gcc/gimple.h 2020-03-25 15:26:38.045052864 +0100 @@ -4728,6 +4728,18 @@ is_gimple_debug (const gimple *gs) } +/* Return the first nondebug statement in GIMPLE sequence S. */ + +static inline gimple * +gimple_seq_first_nondebug_stmt (gimple_seq s) +{ + gimple_seq_node n = gimple_seq_first (s); + while (n && is_gimple_debug (n)) + n = n->next; + return n; +} + + /* Return the last nondebug statement in GIMPLE sequence S. */ static inline gimple * @@ -4737,7 +4749,7 @@ gimple_seq_last_nondebug_stmt (gimple_se for (n = gimple_seq_last (s); n && is_gimple_debug (n); n = n->prev) - if (n->prev == s) + if (n == s) return NULL; return n; } --- gcc/gimplify.c.jj 2020-03-25 14:34:07.722199170 +0100 +++ gcc/gimplify.c 2020-03-25 14:41:46.447348434 +0100 @@ -14849,7 +14849,7 @@ gimplify_body (tree fndecl, bool do_parm /* Gimplify the function's body. */ seq = NULL; gimplify_stmt (&DECL_SAVED_TREE (fndecl), &seq); - outer_stmt = gimple_seq_first_stmt (seq); + outer_stmt = gimple_seq_first_nondebug_stmt (seq); if (!outer_stmt) { outer_stmt = gimple_build_nop (); @@ -14859,8 +14859,37 @@ gimplify_body (tree fndecl, bool do_parm /* The body must contain exactly one statement, a GIMPLE_BIND. If this is not the case, wrap everything in a GIMPLE_BIND to make it so. */ if (gimple_code (outer_stmt) == GIMPLE_BIND - && gimple_seq_first (seq) == gimple_seq_last (seq)) - outer_bind = as_a <gbind *> (outer_stmt); + && (gimple_seq_first_nondebug_stmt (seq) + == gimple_seq_last_nondebug_stmt (seq))) + { + outer_bind = as_a <gbind *> (outer_stmt); + if (gimple_seq_first_stmt (seq) != outer_stmt + || gimple_seq_last_stmt (seq) != outer_stmt) + { + /* If there are debug stmts before or after outer_stmt, move them + inside of outer_bind body. */ + gimple_stmt_iterator gsi = gsi_for_stmt (outer_stmt, &seq); + gimple_seq second_seq = NULL; + if (gimple_seq_first_stmt (seq) != outer_stmt + && gimple_seq_last_stmt (seq) != outer_stmt) + { + second_seq = gsi_split_seq_after (gsi); + gsi_remove (&gsi, false); + } + else if (gimple_seq_first_stmt (seq) != outer_stmt) + gsi_remove (&gsi, false); + else + { + gsi_remove (&gsi, false); + second_seq = seq; + seq = NULL; + } + gimple_seq_add_seq_without_update (&seq, + gimple_bind_body (outer_bind)); + gimple_seq_add_seq_without_update (&seq, second_seq); + gimple_bind_set_body (outer_bind, seq); + } + } else outer_bind = gimple_build_bind (NULL_TREE, seq, NULL); --- gcc/testsuite/g++.dg/debug/pr94281.C.jj 2020-03-25 14:47:11.241498952 +0100 +++ gcc/testsuite/g++.dg/debug/pr94281.C 2020-03-25 14:45:32.637971196 +0100 @@ -0,0 +1,11 @@ +// PR debug/94281 +// { dg-do compile } +// { dg-options "-O1 -fno-tree-dce -fipa-icf -fno-tree-forwprop -fcompare-debug" } + +void fn1() +{ +} +void fn2() +{ + ; +} Jakub