diff options
Diffstat (limited to 'compiler/optimizing/scheduler.h')
| -rw-r--r-- | compiler/optimizing/scheduler.h | 23 |
1 files changed, 22 insertions, 1 deletions
diff --git a/compiler/optimizing/scheduler.h b/compiler/optimizing/scheduler.h index a97eda7e85..f7180a02d7 100644 --- a/compiler/optimizing/scheduler.h +++ b/compiler/optimizing/scheduler.h @@ -183,7 +183,9 @@ class SchedulingNode : public DeletableArenaObject<kArenaAllocScheduler> { void AddOtherPredecessor(SchedulingNode* predecessor) { // Check whether the predecessor has been added earlier. - if (HasOtherDependency(predecessor)) { + // As an optimization of the scheduling graph, we don't need to create another dependency if + // there is a data dependency between scheduling nodes. + if (HasOtherDependency(predecessor) || HasDataDependency(predecessor)) { return; } other_predecessors_.push_back(predecessor); @@ -362,6 +364,25 @@ class SchedulingGraph : public ValueObject { AddDependency(node, dependency, /*is_data_dependency*/false); } + // Analyze whether the scheduling node has cross-iteration dependencies which mean it uses + // values defined on the previous iteration. + // + // Supported cases: + // + // L: + // v2 = loop_head_phi(v1) + // instr1(v2) + // v1 = instr2 + // goto L + // + // In such cases moving instr2 before instr1 creates intersecting live ranges + // of v1 and v2. As a result a separate register is needed to keep the value + // defined by instr2 which is only used on the next iteration. + // If instr2 is not moved, no additional register is needed. The register + // used by instr1 is reused. + // To prevent such a situation a "other" dependency between instr1 and instr2 must be set. + void AddCrossIterationDependencies(SchedulingNode* node); + // Add dependencies nodes for the given `SchedulingNode`: inputs, environments, and side-effects. void AddDependencies(SchedulingNode* node, bool is_scheduling_barrier = false); |