diff options
Diffstat (limited to 'gcc/shrink-wrap.c')
| -rw-r--r-- | gcc/shrink-wrap.c | 23 |
1 files changed, 16 insertions, 7 deletions
diff --git a/gcc/shrink-wrap.c b/gcc/shrink-wrap.c index e51bd36..84abd6b 100644 --- a/gcc/shrink-wrap.c +++ b/gcc/shrink-wrap.c @@ -750,9 +750,21 @@ try_shrink_wrapping (edge *entry_edge, bitmap_head *bb_with, /* If we can move PRO back without having to duplicate more blocks, do so. We do this because putting the prologue earlier is better for scheduling. + We can move back to a block PRE if every path from PRE will eventually need a prologue, that is, PRO is a post-dominator of PRE. PRE needs - to dominate every block reachable from itself. */ + to dominate every block reachable from itself. We keep in BB_TMP a + bitmap of the blocks reachable from PRE that we already found, and in + VEC a stack of those we still need to consider. + + Any block reachable from PRE is also reachable from all predecessors + of PRE, so if we find we need to move PRE back further we can leave + everything not considered so far on the stack. Any block dominated + by PRE is also dominated by all other dominators of PRE, so anything + found good for some PRE does not need to be reconsidered later. + + We don't need to update BB_WITH because none of the new blocks found + can jump to a block that does not need the prologue. */ if (pro != entry) { @@ -775,18 +787,15 @@ try_shrink_wrapping (edge *entry_edge, bitmap_head *bb_with, bool ok = true; while (!vec.is_empty ()) { - basic_block bb = vec.pop (); - bitmap_set_bit (bb_tmp, pre->index); - - if (!dominated_by_p (CDI_DOMINATORS, bb, pre)) + if (!dominated_by_p (CDI_DOMINATORS, vec.last (), pre)) { ok = false; break; } + basic_block bb = vec.pop (); FOR_EACH_EDGE (e, ei, bb->succs) - if (!bitmap_bit_p (bb_with, e->dest->index) - && bitmap_set_bit (bb_tmp, e->dest->index)) + if (bitmap_set_bit (bb_tmp, e->dest->index)) vec.quick_push (e->dest); } |