Relax the only one back-edge restriction.
The rule is in the way for better register allocation, as
it creates an artificial join point between multiple paths.
Change-Id: Ia4392890f95bcea56d143138f28ddce6c572ad58
diff --git a/compiler/optimizing/graph_checker.cc b/compiler/optimizing/graph_checker.cc
index 8ea8f3c..bb27a94 100644
--- a/compiler/optimizing/graph_checker.cc
+++ b/compiler/optimizing/graph_checker.cc
@@ -288,6 +288,7 @@
void SSAChecker::CheckLoop(HBasicBlock* loop_header) {
int id = loop_header->GetBlockId();
+ HLoopInformation* loop_information = loop_header->GetLoopInformation();
// Ensure the pre-header block is first in the list of
// predecessors of a loop header.
@@ -297,57 +298,48 @@
id));
}
- // Ensure the loop header has only two predecessors and that only the
- // second one is a back edge.
+ // Ensure the loop header has only one incoming branch and the remaining
+ // predecessors are back edges.
size_t num_preds = loop_header->GetPredecessors().Size();
if (num_preds < 2) {
AddError(StringPrintf(
"Loop header %d has less than two predecessors: %zu.",
id,
num_preds));
- } else if (num_preds > 2) {
- AddError(StringPrintf(
- "Loop header %d has more than two predecessors: %zu.",
- id,
- num_preds));
} else {
- HLoopInformation* loop_information = loop_header->GetLoopInformation();
HBasicBlock* first_predecessor = loop_header->GetPredecessors().Get(0);
if (loop_information->IsBackEdge(*first_predecessor)) {
AddError(StringPrintf(
"First predecessor of loop header %d is a back edge.",
id));
}
- HBasicBlock* second_predecessor = loop_header->GetPredecessors().Get(1);
- if (!loop_information->IsBackEdge(*second_predecessor)) {
- AddError(StringPrintf(
- "Second predecessor of loop header %d is not a back edge.",
- id));
+ for (size_t i = 1, e = loop_header->GetPredecessors().Size(); i < e; ++i) {
+ HBasicBlock* predecessor = loop_header->GetPredecessors().Get(i);
+ if (!loop_information->IsBackEdge(*predecessor)) {
+ AddError(StringPrintf(
+ "Loop header %d has multiple incoming (non back edge) blocks.",
+ id));
+ }
}
}
- const ArenaBitVector& loop_blocks = loop_header->GetLoopInformation()->GetBlocks();
+ const ArenaBitVector& loop_blocks = loop_information->GetBlocks();
- // Ensure there is only one back edge per loop.
- size_t num_back_edges =
- loop_header->GetLoopInformation()->GetBackEdges().Size();
+ // Ensure back edges belong to the loop.
+ size_t num_back_edges = loop_information->GetBackEdges().Size();
if (num_back_edges == 0) {
AddError(StringPrintf(
"Loop defined by header %d has no back edge.",
id));
- } else if (num_back_edges > 1) {
- AddError(StringPrintf(
- "Loop defined by header %d has several back edges: %zu.",
- id,
- num_back_edges));
} else {
- DCHECK_EQ(num_back_edges, 1u);
- int back_edge_id = loop_header->GetLoopInformation()->GetBackEdges().Get(0)->GetBlockId();
- if (!loop_blocks.IsBitSet(back_edge_id)) {
- AddError(StringPrintf(
- "Loop defined by header %d has an invalid back edge %d.",
- id,
- back_edge_id));
+ for (size_t i = 0; i < num_back_edges; ++i) {
+ int back_edge_id = loop_information->GetBackEdges().Get(i)->GetBlockId();
+ if (!loop_blocks.IsBitSet(back_edge_id)) {
+ AddError(StringPrintf(
+ "Loop defined by header %d has an invalid back edge %d.",
+ id,
+ back_edge_id));
+ }
}
}