diff options
Diffstat (limited to 'gcc/tree-ssa-threadupdate.c')
| -rw-r--r-- | gcc/tree-ssa-threadupdate.c | 49 |
1 files changed, 39 insertions, 10 deletions
diff --git a/gcc/tree-ssa-threadupdate.c b/gcc/tree-ssa-threadupdate.c index c527206..3dd0e4f 100644 --- a/gcc/tree-ssa-threadupdate.c +++ b/gcc/tree-ssa-threadupdate.c @@ -2370,11 +2370,13 @@ static bool valid_jump_thread_path (vec<jump_thread_edge *> *path) { unsigned len = path->length (); - bool multiway_branch = false; + bool threaded_multiway_branch = false; + bool multiway_branch_in_path = false; bool threaded_through_latch = false; /* Check that the path is connected and see if there's a multi-way - branch on the path. */ + branch on the path and whether or not a multi-way branch + is threaded. */ for (unsigned int j = 0; j < len - 1; j++) { edge e = (*path)[j]->e; @@ -2394,7 +2396,12 @@ valid_jump_thread_path (vec<jump_thread_edge *> *path) threaded_through_latch = true; gimple *last = last_stmt (e->dest); - multiway_branch |= (last && gimple_code (last) == GIMPLE_SWITCH); + if (j == len - 2) + threaded_multiway_branch + |= (last && gimple_code (last) == GIMPLE_SWITCH); + else + multiway_branch_in_path + |= (last && gimple_code (last) == GIMPLE_SWITCH); } /* If we are trying to thread through the loop latch to a block in the @@ -2402,8 +2409,33 @@ valid_jump_thread_path (vec<jump_thread_edge *> *path) irreducible loop. We avoid that unless the jump thread has a multi-way branch, in which case we have deemed it worth losing other loop optimizations later if we can eliminate the multi-way branch. */ - if (!multiway_branch && threaded_through_latch) - return false; + if (!threaded_multiway_branch && threaded_through_latch) + { + if (dump_file && (dump_flags & TDF_DETAILS)) + { + fprintf (dump_file, + "Thread through latch without threading a multiway " + "branch.\n"); + dump_jump_thread_path (dump_file, *path, false); + } + return false; + } + + /* When there is a multi-way branch on the path, then threading can + explode the CFG due to duplicating the edges for that multi-way + branch. So like above, only allow a multi-way branch on the path + if we actually thread a multi-way branch. */ + if (!threaded_multiway_branch && multiway_branch_in_path) + { + if (dump_file && (dump_flags & TDF_DETAILS)) + { + fprintf (dump_file, + "Thread through multiway branch without threading " + "a multiway branch.\n"); + dump_jump_thread_path (dump_file, *path, false); + } + return false; + } return true; } @@ -2494,11 +2526,8 @@ thread_through_all_blocks (bool may_peel_loop_headers) /* Do not jump-thread twice from the same block. */ if (bitmap_bit_p (threaded_blocks, entry->src->index) - /* Verify that the jump thread path is still valid: a - previous jump-thread may have changed the CFG, and - invalidated the current path or the requested jump - thread might create irreducible loops which should - generally be avoided. */ + /* We may not want to realize this jump thread path + for various reasons. So check it first. */ || !valid_jump_thread_path (path)) { /* Remove invalid FSM jump-thread paths. */ |