pr42739.C, complicated by some extra wrappers and cleanups from a
feature I'm working on, got me very confused because a user label
ended up in a cleanup introduced by my pass, where it couldn't
possibly have been initially.
The current logic may move such an unreachable user label multiple
times, if it ends up in blocks that get removed one after the other.
Since it doesn't really matter where it lands (save for omp
constraints), I propose we move it once and for all to a stable, final
location, that we currently use only as a last resort: the entry
point.
Regstrapped on x86_64-linux-gnu. Ok to install?
for gcc/ChangeLog
* tree-cfg.c (remove_bb): When preserving an unreachable user
label, use the entry block as the preferred choice for its
surviving location, rather than as a last resort.
---
gcc/tree-cfg.c | 18 +++++-------------
1 file changed, 5 insertions(+), 13 deletions(-)
diff --git a/gcc/tree-cfg.c b/gcc/tree-cfg.c
index 1f0f4a2c6eb2c..f6f005f10a9f5 100644
--- a/gcc/tree-cfg.c
+++ b/gcc/tree-cfg.c
@@ -2300,13 +2300,11 @@ remove_bb (basic_block bb)
FORCED_LABEL (gimple_label_label (label_stmt)) = 1;
}
- new_bb = bb->prev_bb;
- /* Don't move any labels into ENTRY block. */
- if (new_bb == ENTRY_BLOCK_PTR_FOR_FN (cfun))
- {
- new_bb = single_succ (new_bb);
- gcc_assert (new_bb != bb);
- }
+ /* We have to move the unreachable label somewhere.
+ Moving it to the entry block makes sure it's moved at
+ most once, and avoids messing with anonymous landing
+ pad labels. */
+ new_bb = single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun));
if ((unsigned) bb->index < bb_to_omp_idx.length ()
&& ((unsigned) new_bb->index >= bb_to_omp_idx.length ()
|| (bb_to_omp_idx[bb->index]
@@ -2316,7 +2314,6 @@ remove_bb (basic_block bb)
into the right OMP region. */
unsigned int i;
int idx;
- new_bb = NULL;
FOR_EACH_VEC_ELT (bb_to_omp_idx, i, idx)
if (i >= NUM_FIXED_BLOCKS
&& idx == bb_to_omp_idx[bb->index]
@@ -2325,11 +2322,6 @@ remove_bb (basic_block bb)
new_bb = BASIC_BLOCK_FOR_FN (cfun, i);
break;
}
- if (new_bb == NULL)
- {
- new_bb = single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun));
- gcc_assert (new_bb != bb);
- }
}
new_gsi = gsi_after_labels (new_bb);
gsi_remove (&i, false);
--
Alexandre Oliva, happy hacker https://FSFLA.org/blogs/lxo/
Free Software Activist GNU Toolchain Engineer
Disinformation flourishes because many people care deeply about injustice
but very few check the facts. Ask me about <https://stallmansupport.org>
