Improve code generation for bounds checks.

src/arm64/lithium-arm64.cc

Index: src/arm64/lithium-arm64.cc
diff --git a/src/arm64/lithium-arm64.cc b/src/arm64/lithium-arm64.cc
index adc2b5c916e47911c06fe4e62bf37e26eae1b15b..8682e2b82fc190cce90c98b6c2a01f7d1635b9fa 100644
--- a/src/arm64/lithium-arm64.cc
+++ b/src/arm64/lithium-arm64.cc
@@ -949,9 +949,16 @@ LInstruction* LChunkBuilder::DoBlockEntry(HBlockEntry* instr) {
 
 
 LInstruction* LChunkBuilder::DoBoundsCheck(HBoundsCheck* instr) {
-  LOperand* value = UseRegisterOrConstantAtStart(instr->index());
-  LOperand* length = UseRegister(instr->length());
-  return AssignEnvironment(new(zone()) LBoundsCheck(value, length));
+  if (!FLAG_debug_code && instr->skip_check()) return NULL;
+  LOperand* index = UseRegisterOrConstantAtStart(instr->index());
+  LOperand* length = !index->IsConstantOperand()
+      ? UseRegisterOrConstantAtStart(instr->length())
+      : UseRegisterAtStart(instr->length());
+  LInstruction* result = new(zone()) LBoundsCheck(index, length);
+  if (!FLAG_debug_code || !instr->skip_check()) {
+    result = AssignEnvironment(result);
+  }
+  return result;
 }