Implement irreducible loop support in optimizing.
So we don't fallback to the interpreter in the presence of
irreducible loops.
Implications:
- A loop pre-header does not necessarily dominate a loop header.
- Non-constant redundant phis will be kept in loop headers, to
satisfy our linear scan register allocation algorithm.
- while-graph optimizations, such as gvn, licm, lse, and dce
need to know when they are dealing with irreducible loops.
Change-Id: I2cea8934ce0b40162d215353497c7f77d6c9137e
diff --git a/compiler/optimizing/load_store_elimination.cc b/compiler/optimizing/load_store_elimination.cc
index 2b313f6..c4492c8 100644
--- a/compiler/optimizing/load_store_elimination.cc
+++ b/compiler/optimizing/load_store_elimination.cc
@@ -582,9 +582,22 @@
DCHECK(block->IsLoopHeader());
int block_id = block->GetBlockId();
ArenaVector<HInstruction*>& heap_values = heap_values_for_[block_id];
+
+ // Don't eliminate loads in irreducible loops. This is safe for singletons, because
+ // they are always used by the non-eliminated loop-phi.
+ if (block->GetLoopInformation()->IsIrreducible()) {
+ if (kIsDebugBuild) {
+ for (size_t i = 0; i < heap_values.size(); i++) {
+ DCHECK_EQ(heap_values[i], kUnknownHeapValue);
+ }
+ }
+ return;
+ }
+
HBasicBlock* pre_header = block->GetLoopInformation()->GetPreHeader();
ArenaVector<HInstruction*>& pre_header_heap_values =
heap_values_for_[pre_header->GetBlockId()];
+
// Inherit the values from pre-header.
for (size_t i = 0; i < heap_values.size(); i++) {
heap_values[i] = pre_header_heap_values[i];