diff options
Diffstat (limited to 'gcc/tree-ssa-dse.c')
| -rw-r--r-- | gcc/tree-ssa-dse.c | 27 |
1 files changed, 16 insertions, 11 deletions
diff --git a/gcc/tree-ssa-dse.c b/gcc/tree-ssa-dse.c index 37a5481..b678a8f 100644 --- a/gcc/tree-ssa-dse.c +++ b/gcc/tree-ssa-dse.c @@ -161,7 +161,7 @@ dse_possible_dead_store_p (gimple stmt, gimple *use_stmt) temp = stmt; do { - gimple prev, use_stmt; + gimple use_stmt; imm_use_iterator ui; bool fail = false; tree defvar; @@ -175,28 +175,33 @@ dse_possible_dead_store_p (gimple stmt, gimple *use_stmt) defvar = PHI_RESULT (temp); else defvar = gimple_vdef (temp); - prev = temp; temp = NULL; FOR_EACH_IMM_USE_STMT (use_stmt, ui, defvar) { cnt++; + /* If we ever reach our DSE candidate stmt again fail. We + cannot handle dead stores in loops. */ + if (use_stmt == stmt) + { + fail = true; + BREAK_FROM_IMM_USE_STMT (ui); + } /* In simple cases we can look through PHI nodes, but we have to be careful with loops and with memory references containing operands that are also operands of PHI nodes. See gcc.c-torture/execute/20051110-*.c. */ - if (gimple_code (use_stmt) == GIMPLE_PHI) + else if (gimple_code (use_stmt) == GIMPLE_PHI) { if (temp - /* We can look through PHIs to post-dominated regions - without worrying if the use not also dominates prev - (in which case it would be a loop PHI with the use - in a latch block). */ - || gimple_bb (prev) == gimple_bb (use_stmt) - || !dominated_by_p (CDI_POST_DOMINATORS, - gimple_bb (prev), gimple_bb (use_stmt)) + /* Make sure we are not in a loop latch block. */ + || gimple_bb (stmt) == gimple_bb (use_stmt) || dominated_by_p (CDI_DOMINATORS, - gimple_bb (prev), gimple_bb (use_stmt))) + gimple_bb (stmt), gimple_bb (use_stmt)) + /* We can look through PHIs to regions post-dominating + the DSE candidate stmt. */ + || !dominated_by_p (CDI_POST_DOMINATORS, + gimple_bb (stmt), gimple_bb (use_stmt))) { fail = true; BREAK_FROM_IMM_USE_STMT (ui); |