Account for early exit loop.
Rationale:
last value computation is obviously only right if
the loop does not have early exits; only needed
if cycle leaks to outside loop in any way.
Bug:32633772
Test: 623-checker-loop-regressions
Change-Id: Id60beca4704491cff611ad12a24bfc63c09d32c3
diff --git a/compiler/optimizing/loop_optimization.cc b/compiler/optimizing/loop_optimization.cc
index 55e1a2c..f4616e3 100644
--- a/compiler/optimizing/loop_optimization.cc
+++ b/compiler/optimizing/loop_optimization.cc
@@ -28,7 +28,7 @@
instruction->GetBlock()->RemoveInstructionOrPhi(instruction, /*ensure_safety=*/ false);
}
-// Detects a goto block and sets succ to the single successor.
+// Detect a goto block and sets succ to the single successor.
static bool IsGotoBlock(HBasicBlock* block, /*out*/ HBasicBlock** succ) {
if (block->GetPredecessors().size() == 1 &&
block->GetSuccessors().size() == 1 &&
@@ -39,6 +39,19 @@
return false;
}
+// Detect an early exit loop.
+static bool IsEarlyExit(HLoopInformation* loop_info) {
+ HBlocksInLoopReversePostOrderIterator it_loop(*loop_info);
+ for (it_loop.Advance(); !it_loop.Done(); it_loop.Advance()) {
+ for (HBasicBlock* successor : it_loop.Current()->GetSuccessors()) {
+ if (!loop_info->Contains(*successor)) {
+ return true;
+ }
+ }
+ }
+ return false;
+}
+
//
// Class methods.
//
@@ -179,7 +192,9 @@
int32_t use_count = 0;
if (IsPhiInduction(phi) &&
IsOnlyUsedAfterLoop(node->loop_info, phi, &use_count) &&
- TryReplaceWithLastValue(phi, use_count, preheader)) {
+ // No uses, or no early-exit with proper replacement.
+ (use_count == 0 ||
+ (!IsEarlyExit(node->loop_info) && TryReplaceWithLastValue(phi, preheader)))) {
for (HInstruction* i : *iset_) {
RemoveFromCycle(i);
}
@@ -277,7 +292,8 @@
if (IsEmptyHeader(header) &&
IsEmptyBody(body) &&
IsOnlyUsedAfterLoop(node->loop_info, header->GetFirstPhi(), &use_count) &&
- TryReplaceWithLastValue(header->GetFirstPhi(), use_count, preheader)) {
+ // No uses, or proper replacement.
+ (use_count == 0 || TryReplaceWithLastValue(header->GetFirstPhi(), preheader))) {
body->DisconnectAndDelete();
exit->RemovePredecessor(header);
header->RemoveSuccessor(exit);
@@ -395,20 +411,16 @@
}
}
-bool HLoopOptimization::TryReplaceWithLastValue(HInstruction* instruction,
- int32_t use_count,
- HBasicBlock* block) {
- // If true uses appear after the loop, replace these uses with the last value. Environment
- // uses can consume this value too, since any first true use is outside the loop (although
- // this may imply that de-opting may look "ahead" a bit on the phi value). If there are only
- // environment uses, the value is dropped altogether, since the computations have no effect.
- if (use_count > 0) {
- if (!induction_range_.CanGenerateLastValue(instruction)) {
- return false;
- }
+bool HLoopOptimization::TryReplaceWithLastValue(HInstruction* instruction, HBasicBlock* block) {
+ // Try to replace outside uses with the last value. Environment uses can consume this
+ // value too, since any first true use is outside the loop (although this may imply
+ // that de-opting may look "ahead" a bit on the phi value). If there are only environment
+ // uses, the value is dropped altogether, since the computations have no effect.
+ if (induction_range_.CanGenerateLastValue(instruction)) {
ReplaceAllUses(instruction, induction_range_.GenerateLastValue(instruction, graph_, block));
+ return true;
}
- return true;
+ return false;
}
} // namespace art