- Canonicalize array bounds checks to avoid deopting when comparing

runtime/vm/intermediate_language_arm.cc

Index: runtime/vm/intermediate_language_arm.cc
===================================================================
--- runtime/vm/intermediate_language_arm.cc	(revision 22689)
+++ runtime/vm/intermediate_language_arm.cc	(working copy)
@@ -2503,8 +2503,8 @@
   const intptr_t kNumTemps = 0;
   LocationSummary* locs =
       new LocationSummary(kNumInputs, kNumTemps, LocationSummary::kNoCall);
-  locs->set_in(0, Location::RegisterOrSmiConstant(length()));
-  locs->set_in(1, Location::RegisterOrSmiConstant(index()));
+  locs->set_in(locLength, Location::RegisterOrSmiConstant(length()));
+  locs->set_in(locIndex, Location::RegisterOrSmiConstant(index()));
   return locs;
 }
 
@@ -2512,28 +2512,31 @@
 void CheckArrayBoundInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
   Label* deopt = compiler->AddDeoptStub(deopt_id(),
                                         kDeoptCheckArrayBound);
-  if (locs()->in(0).IsConstant() && locs()->in(1).IsConstant()) {
+  if (locs()->in(locLength).IsConstant() && locs()->in(locIndex).IsConstant()) {
+    ASSERT((Smi::Cast(locs()->in(locLength).constant()).Value() <=
+            Smi::Cast(locs()->in(locIndex).constant()).Value()) ||
+           (Smi::Cast(locs()->in(locIndex).constant()).Value() < 0));
     // Unconditionally deoptimize for constant bounds checks because they
     // only occur only when index is out-of-bounds.
     __ b(deopt);
     return;
   }
 
-  if (locs()->in(1).IsConstant()) {
-    Register length = locs()->in(0).reg();
-    const Object& constant = locs()->in(1).constant();
+  if (locs()->in(locIndex).IsConstant()) {
+    Register length = locs()->in(locLength).reg();
+    const Object& constant = locs()->in(locIndex).constant();
     ASSERT(constant.IsSmi());
     __ CompareImmediate(length, reinterpret_cast<int32_t>(constant.raw()));
     __ b(deopt, LS);
-  } else if (locs()->in(0).IsConstant()) {
-    ASSERT(locs()->in(0).constant().IsSmi());
-    const Smi& smi_const = Smi::Cast(locs()->in(0).constant());
-    Register index = locs()->in(1).reg();
+  } else if (locs()->in(locLength).IsConstant()) {
+    ASSERT(locs()->in(locLength).constant().IsSmi());
+    const Smi& smi_const = Smi::Cast(locs()->in(locLength).constant());
+    Register index = locs()->in(locIndex).reg();
     __ CompareImmediate(index, reinterpret_cast<int32_t>(smi_const.raw()));
     __ b(deopt, CS);
   } else {
-    Register length = locs()->in(0).reg();
-    Register index = locs()->in(1).reg();
+    Register length = locs()->in(locLength).reg();
+    Register index = locs()->in(locIndex).reg();
     __ cmp(index, ShifterOperand(length));
     __ b(deopt, CS);
   }