diff options
| author | Richard Biener <rguenther@suse.de> | 2021-08-27 09:47:49 +0200 |
|---|---|---|
| committer | Richard Biener <rguenther@suse.de> | 2021-08-27 09:51:26 +0200 |
| commit | 41439e1f6d2da1e86538c726f0603cffd5dd098e (patch) | |
| tree | 65fca8bcd2717417c16756e02f9a2270e859da91 /gcc/tree-ssa-dce.c | |
| parent | 44a545a6abdd330083c1d12ad70092defbba702a (diff) | |
| download | gcc-41439e1f6d2da1e86538c726f0603cffd5dd098e.zip gcc-41439e1f6d2da1e86538c726f0603cffd5dd098e.tar.gz gcc-41439e1f6d2da1e86538c726f0603cffd5dd098e.tar.bz2 | |
tree-optimization/45178 - DCE of dead control flow in infinite loop
This fixes DCE to be able to elide dead control flow in an
infinite loop without an exit edge. This special situation is
handled well by the code finding an edge to preserve since there's
no chance it will find the exit edge and make the loop finite.
2021-08-27 Richard Biener <rguenther@suse.de>
PR tree-optimization/45178
* tree-ssa-dce.c (find_obviously_necessary_stmts): For
infinite loops without exit do not mark control dependent
edges of the latch necessary.
* gcc.dg/tree-ssa/ssa-dce-3.c: Adjust testcase.
Diffstat (limited to 'gcc/tree-ssa-dce.c')
| -rw-r--r-- | gcc/tree-ssa-dce.c | 14 |
1 files changed, 9 insertions, 5 deletions
diff --git a/gcc/tree-ssa-dce.c b/gcc/tree-ssa-dce.c index 0778eb9..c4907af 100644 --- a/gcc/tree-ssa-dce.c +++ b/gcc/tree-ssa-dce.c @@ -414,7 +414,9 @@ find_obviously_necessary_stmts (bool aggressive) if ((flags & (ECF_CONST|ECF_PURE)) && !(flags & ECF_LOOPING_CONST_OR_PURE)) return; - /* Prevent the empty possibly infinite loops from being removed. */ + /* Prevent the empty possibly infinite loops from being removed. This is + needed to make the logic in remove_dead_stmt work to identify the + correct edge to keep when removing a controlling condition. */ if (aggressive) { if (mark_irreducible_loops ()) @@ -426,17 +428,19 @@ find_obviously_necessary_stmts (bool aggressive) && (e->flags & EDGE_IRREDUCIBLE_LOOP)) { if (dump_file) - fprintf (dump_file, "Marking back edge of irreducible loop %i->%i\n", - e->src->index, e->dest->index); + fprintf (dump_file, "Marking back edge of irreducible " + "loop %i->%i\n", e->src->index, e->dest->index); mark_control_dependent_edges_necessary (e->dest, false); } } for (auto loop : loops_list (cfun, 0)) - if (!finite_loop_p (loop)) + /* For loops without an exit do not mark any condition. */ + if (loop->exits->next && !finite_loop_p (loop)) { if (dump_file) - fprintf (dump_file, "cannot prove finiteness of loop %i\n", loop->num); + fprintf (dump_file, "cannot prove finiteness of loop %i\n", + loop->num); mark_control_dependent_edges_necessary (loop->latch, false); } } |