2 files changed, 43 insertions, 3 deletions

diff --git a/compiler/optimizing/register_allocator_test.cc b/compiler/optimizing/register_allocator_test.cc
index bfabc5ad27..a7283ab329 100644
--- a/compiler/optimizing/register_allocator_test.cc
+++ b/compiler/optimizing/register_allocator_test.cc
@@ -318,4 +318,42 @@ TEST(RegisterAllocatorTest, Loop3) {
   ASSERT_EQ(phi_interval->GetRegister(), ret->InputAt(0)->GetLiveInterval()->GetRegister());
 }
 
+TEST(RegisterAllocatorTest, FirstRegisterUse) {
+  const uint16_t data[] = THREE_REGISTERS_CODE_ITEM(
+    Instruction::CONST_4 | 0 | 0,
+    Instruction::ADD_INT_LIT8 | 1 << 8, 1 << 8,
+    Instruction::ADD_INT_LIT8 | 0 << 8, 1 << 8,
+    Instruction::ADD_INT_LIT8 | 1 << 8, 1 << 8 | 1,
+    Instruction::RETURN_VOID);
+
+  ArenaPool pool;
+  ArenaAllocator allocator(&pool);
+  HGraph* graph = BuildSSAGraph(data, &allocator);
+  CodeGenerator* codegen = CodeGenerator::Create(&allocator, graph, kArm);
+  SsaLivenessAnalysis liveness(*graph, codegen);
+  liveness.Analyze();
+
+  HAdd* first_add = graph->GetBlocks().Get(1)->GetFirstInstruction()->AsAdd();
+  HAdd* last_add = graph->GetBlocks().Get(1)->GetLastInstruction()->GetPrevious()->AsAdd();
+  ASSERT_EQ(last_add->InputAt(0), first_add);
+  LiveInterval* interval = first_add->GetLiveInterval();
+  ASSERT_EQ(interval->GetEnd(), last_add->GetLifetimePosition() + 1);
+  ASSERT_TRUE(interval->GetNextSibling() == nullptr);
+
+  // We need a register for the output of the instruction.
+  ASSERT_EQ(interval->FirstRegisterUse(), first_add->GetLifetimePosition());
+
+  // Split at the next instruction.
+  interval = interval->SplitAt(first_add->GetLifetimePosition() + 2);
+  // The user of the split is the last add.
+  ASSERT_EQ(interval->FirstRegisterUse(), last_add->GetLifetimePosition() + 1);
+
+  // Split before the last add.
+  LiveInterval* new_interval = interval->SplitAt(last_add->GetLifetimePosition() - 1);
+  // Ensure the current interval has no register use...
+  ASSERT_EQ(interval->FirstRegisterUse(), kNoLifetime);
+  // And the new interval has it for the last add.
+  ASSERT_EQ(new_interval->FirstRegisterUse(), last_add->GetLifetimePosition() + 1);
+}
+
 }  // namespace art
diff --git a/compiler/optimizing/ssa_liveness_analysis.h b/compiler/optimizing/ssa_liveness_analysis.h
index fc3eb660d5..83035b52f6 100644
--- a/compiler/optimizing/ssa_liveness_analysis.h
+++ b/compiler/optimizing/ssa_liveness_analysis.h
@@ -289,21 +289,23 @@ class LiveInterval : public ArenaObject {
 
   size_t FirstRegisterUseAfter(size_t position) const {
     if (position == GetStart() && defined_by_ != nullptr) {
-      Location location = defined_by_->GetLocations()->Out();
+      LocationSummary* locations = defined_by_->GetLocations();
+      Location location = locations->Out();
       // This interval is the first interval of the instruction. If the output
       // of the instruction requires a register, we return the position of that instruction
       // as the first register use.
       if (location.IsUnallocated()) {
         if ((location.GetPolicy() == Location::kRequiresRegister)
              || (location.GetPolicy() == Location::kSameAsFirstInput
-                && defined_by_->GetLocations()->InAt(0).GetPolicy() == Location::kRequiresRegister)) {
+                 && locations->InAt(0).GetPolicy() == Location::kRequiresRegister)) {
           return position;
         }
       }
     }
 
     UsePosition* use = first_use_;
-    while (use != nullptr) {
+    size_t end = GetEnd();
+    while (use != nullptr && use->GetPosition() <= end) {
       size_t use_position = use->GetPosition();
       if (use_position >= position && !use->GetIsEnvironment()) {
         Location location = use->GetUser()->GetLocations()->InAt(use->GetInputIndex());