diff options
Diffstat (limited to 'gcc/tree-ssa-threadupdate.c')
| -rw-r--r-- | gcc/tree-ssa-threadupdate.c | 62 |
1 files changed, 62 insertions, 0 deletions
diff --git a/gcc/tree-ssa-threadupdate.c b/gcc/tree-ssa-threadupdate.c index 2adea1b..3e34567 100644 --- a/gcc/tree-ssa-threadupdate.c +++ b/gcc/tree-ssa-threadupdate.c @@ -1354,6 +1354,68 @@ mark_threaded_blocks (bitmap threaded_blocks) else bitmap_copy (threaded_blocks, tmp); + /* Look for jump threading paths which cross multiple loop headers. + + The code to thread through loop headers will change the CFG in ways + that break assumptions made by the loop optimization code. + + We don't want to blindly cancel the requests. We can instead do better + by trimming off the end of the jump thread path. */ + EXECUTE_IF_SET_IN_BITMAP (tmp, 0, i, bi) + { + basic_block bb = BASIC_BLOCK (i); + FOR_EACH_EDGE (e, ei, bb->preds) + { + if (e->aux) + { + vec<jump_thread_edge *> *path = THREAD_PATH (e); + + /* Basically we're looking for a situation where we can see + 3 or more loop structures on a jump threading path. */ + + struct loop *first_father = (*path)[0]->e->src->loop_father; + struct loop *second_father = NULL; + for (unsigned int i = 0; i < path->length (); i++) + { + /* See if this is a loop father we have not seen before. */ + if ((*path)[i]->e->dest->loop_father != first_father + && (*path)[i]->e->dest->loop_father != second_father) + { + /* We've already seen two loop fathers, so we + need to trim this jump threading path. */ + if (second_father != NULL) + { + /* Trim from entry I onwards. */ + for (unsigned int j = i; j < path->length (); j++) + delete (*path)[j]; + path->truncate (i); + + /* Now that we've truncated the path, make sure + what's left is still valid. We need at least + two edges on the path and the last edge can not + be a joiner. This should never happen, but let's + be safe. */ + if (path->length () < 2 + || (path->last ()->type + == EDGE_COPY_SRC_JOINER_BLOCK)) + { + for (unsigned int i = 0; i < path->length (); i++) + delete (*path)[i]; + path->release (); + e->aux = NULL; + } + break; + } + else + { + second_father = (*path)[i]->e->dest->loop_father; + } + } + } + } + } + } + BITMAP_FREE (tmp); } |