Fix a bug in SSA construction.
If a join block does not have an incoming value for a local
from a predecessor block, we should not create a phi. The
verifier has made sure the local is updated before any
following reads after this block.
Change-Id: Id2785efc73c9fb3224826fff2f4b4ad215905ff4
diff --git a/compiler/optimizing/ssa_builder.cc b/compiler/optimizing/ssa_builder.cc
index 33084df..1284a97 100644
--- a/compiler/optimizing/ssa_builder.cc
+++ b/compiler/optimizing/ssa_builder.cc
@@ -95,14 +95,26 @@
// All predecessors have already been visited because we are visiting in reverse post order.
// We merge the values of all locals, creating phis if those values differ.
for (size_t local = 0; local < current_locals_->Size(); local++) {
+ bool one_predecessor_has_no_value = false;
bool is_different = false;
HInstruction* value = ValueOfLocal(block->GetPredecessors().Get(0), local);
- for (size_t i = 1; i < block->GetPredecessors().Size(); i++) {
- if (ValueOfLocal(block->GetPredecessors().Get(i), local) != value) {
+
+ for (size_t i = 0, e = block->GetPredecessors().Size(); i < e; ++i) {
+ HInstruction* current = ValueOfLocal(block->GetPredecessors().Get(i), local);
+ if (current == nullptr) {
+// one_predecessor_has_no_value = true;
+// break;
+ } else if (current != value) {
is_different = true;
- break;
}
}
+
+ if (one_predecessor_has_no_value) {
+ // If one predecessor has no value for this local, we trust the verifier has
+ // successfully checked that there is a store dominating any read after this block.
+ continue;
+ }
+
if (is_different) {
HPhi* phi = new (GetGraph()->GetArena()) HPhi(
GetGraph()->GetArena(), local, block->GetPredecessors().Size(), Primitive::kPrimVoid);