I recently noticed that we were failing to propagate edge equivalences
into PHI arguments in non-dominated successors.
The case loos like this:
;; basic block 11, loop depth 0, count 0, freq 160, maybe hot
;; prev block 10, next block 12, flags: (NEW, REACHABLE)
;; pred: 10 [50.0%] (FALSE_VALUE,EXECUTABLE)
_257 = di_13(D)->comps;
_258 = (long unsigned int) _255;
_259 = _258 * 24;
p_260 = _257 + _259;
_261 = _255 + 1;
di_13(D)->next_comp = _261;
if (p_260 != 0B)
goto <bb 12>;
else
goto <bb 13>;
;; succ: 12 [100.0%] (TRUE_VALUE,EXECUTABLE)
;; 13 (FALSE_VALUE,EXECUTABLE)
;; basic block 12, loop depth 0, count 0, freq 272, maybe hot
;; Invalid sum of incoming frequencies 160, should be 272
;; prev block 11, next block 13, flags: (NEW, REACHABLE)
;; pred: 11 [100.0%] (TRUE_VALUE,EXECUTABLE)
p_260->type = 37;
p_260->u.s_builtin.type = _139;
;; succ: 13 [100.0%] (FALLTHRU,EXECUTABLE)
;; basic block 13, loop depth 0, count 0, freq 319, maybe hot
;; Invalid sum of incoming frequencies 432, should be 319
;; prev block 12, next block 14, flags: (NEW, REACHABLE)
;; pred: 110 [100.0%] (FALLTHRU)
;; 12 [100.0%] (FALLTHRU,EXECUTABLE)
;; 11 (FALSE_VALUE,EXECUTABLE)
# _478 = PHI <0B(110), p_260(12), p_260(11)>
ret = _478;
_142 = di_13(D)->expansion;
_143 = _478->u.s_builtin.type;
In particular note block 11 does *not* dominate block 13. However, we
know that when we traverse the edge 11->13 that p_260 will have the
value zero, which should be propagated into the PHI node.
After fixing the propagation with the attached patch we have
_478 = PHI <0B(110), p_260(12), 0B(11)>
I have other code which then discovers the unconditional NULL pointer
dereferences when we traverse 110->13 or 11->13 and isolates those paths.
That in turn allows blocks 12 and 13 to be combined, which in turn
allows discovery of additional CSE opportunities.
Bootstrapped and regression tested on x86_64-unknown-linux-gnu. Applied
to the trunk.
diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 8493ee1..1f1f939 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2013-09-06 Jeff Law <l...@redhat.com>
+
+ * tree-ssa-dom.c (cprop_into_successor_phis): Also propagate
+ edge implied equivalences into successor phis.
+
2013-09-06 Claudiu Zissulescu <claz...@synopsys.com>
* resource.c (mark_target_live_regs): Compute resources taking
diff --git a/gcc/tree-ssa-dom.c b/gcc/tree-ssa-dom.c
index 691e6f9..f999a64 100644
--- a/gcc/tree-ssa-dom.c
+++ b/gcc/tree-ssa-dom.c
@@ -1642,6 +1642,28 @@ cprop_into_successor_phis (basic_block bb)
if (gsi_end_p (gsi))
continue;
+ /* We may have an equivalence associated with this edge. While
+ we can not propagate it into non-dominated blocks, we can
+ propagate them into PHIs in non-dominated blocks. */
+
+ /* Push the unwind marker so we can reset the const and copies
+ table back to its original state after processing this edge. */
+ const_and_copies_stack.safe_push (NULL_TREE);
+
+ /* Extract and record any simple NAME = VALUE equivalences.
+
+ Don't bother with [01] = COND equivalences, they're not useful
+ here. */
+ struct edge_info *edge_info = (struct edge_info *) e->aux;
+ if (edge_info)
+ {
+ tree lhs = edge_info->lhs;
+ tree rhs = edge_info->rhs;
+
+ if (lhs && TREE_CODE (lhs) == SSA_NAME)
+ record_const_or_copy (lhs, rhs);
+ }
+
indx = e->dest_idx;
for ( ; !gsi_end_p (gsi); gsi_next (&gsi))
{
@@ -1667,6 +1689,8 @@ cprop_into_successor_phis (basic_block bb)
&& may_propagate_copy (orig_val, new_val))
propagate_value (orig_p, new_val);
}
+
+ restore_vars_to_original_value ();
}
}
