diff options
Diffstat (limited to 'gcc/tree-ssa-threadedge.c')
| -rw-r--r-- | gcc/tree-ssa-threadedge.c | 29 |
1 files changed, 21 insertions, 8 deletions
diff --git a/gcc/tree-ssa-threadedge.c b/gcc/tree-ssa-threadedge.c index 14bc4e3..839f185 100644 --- a/gcc/tree-ssa-threadedge.c +++ b/gcc/tree-ssa-threadedge.c @@ -770,7 +770,19 @@ thread_around_empty_blocks (edge taken_edge, gsi = gsi_start_nondebug_bb (bb); /* If the block has no statements, but does have a single successor, then - it's just a forwarding block and we can thread through it trivially. */ + it's just a forwarding block and we can thread through it trivially. + + However, note that just threading through empty blocks with single + successors is not inherently profitable. For the jump thread to + be profitable, we must avoid a runtime conditional. + + By taking the return value from the recursive call, we get the + desired effect of returning TRUE when we found a profitable jump + threading opportunity and FALSE otherwise. + + This is particularly important when this routine is called after + processing a joiner block. Returning TRUE too aggressively in + that case results in pointless duplication of the joiner block. */ if (gsi_end_p (gsi)) { if (single_succ_p (bb)) @@ -781,15 +793,16 @@ thread_around_empty_blocks (edge taken_edge, { bitmap_set_bit (visited, taken_edge->dest->index); path->safe_push (taken_edge); - thread_around_empty_blocks (taken_edge, - dummy_cond, - handle_dominating_asserts, - simplify, - visited, - path); - return true; + return thread_around_empty_blocks (taken_edge, + dummy_cond, + handle_dominating_asserts, + simplify, + visited, + path); } } + + /* We have a block with no statements, but multiple successors? */ return false; } |