While I was looking at differences before and after
r14-569-g21e2ef2dc25de3, I noticed that one phi node was
not being removed.
For an example, while compiling combine.cc, in expand_field_assignment,
we would remove `# pos_51 = PHI <pos_221(31), pos_51(30)>`
but we don't any more since pos_51 has more than zero users
but in this case it is only itself.
This patch improves simple_dce_from_worklist to detect that
case and now we able to remove this phi statement again.
OK? Bootstrapped and tested on x86_64-linux-gnu.
gcc/ChangeLog:
* tree-ssa-dce.cc (simple_dce_from_worklist): For ssa names
defined by a phi node with more than one uses, allow for the
only uses are in that same defining statement.
---
gcc/tree-ssa-dce.cc | 31 +++++++++++++++++++++++++++++--
1 file changed, 29 insertions(+), 2 deletions(-)
diff --git a/gcc/tree-ssa-dce.cc b/gcc/tree-ssa-dce.cc
index 6554b5db03e..045c64a9c02 100644
--- a/gcc/tree-ssa-dce.cc
+++ b/gcc/tree-ssa-dce.cc
@@ -2107,9 +2107,36 @@ simple_dce_from_worklist (bitmap worklist, bitmap
need_eh_cleanup)
unsigned i = bitmap_clear_first_set_bit (worklist);
tree def = ssa_name (i);
- /* Removed by somebody else or still in use. */
+ /* Removed by somebody else or still in use.
+ Note use in itself for a phi node is not counted as still in use. */
if (! def || ! has_zero_uses (def))
- continue;
+ {
+
+ if (!def)
+ continue;
+
+ gimple *def_stmt = SSA_NAME_DEF_STMT (def);
+ if (gimple_code (def_stmt) != GIMPLE_PHI)
+ continue;
+
+ gimple *use_stmt;
+ imm_use_iterator use_iter;
+ bool canremove = true;
+
+ FOR_EACH_IMM_USE_STMT (use_stmt, use_iter, def)
+ {
+ /* Ignore debug statements. */
+ if (is_gimple_debug (use_stmt))
+ continue;
+ if (use_stmt != def_stmt)
+ {
+ canremove = false;
+ break;
+ }
+ }
+ if (!canremove)
+ continue;
+ }
gimple *t = SSA_NAME_DEF_STMT (def);
if (gimple_has_side_effects (t))
--
2.31.1
