Recognize for (int i = 0; i != x.length; i++) loops

Rationale:
Idiom occurs in real-life and is very straightforwardly
recognized by existing induction/range machinery.

Change-Id: I965a16e9de72f3523ea5023d30ed1c4e47ed5010

1 files changed, 8 insertions, 0 deletions

diff --git a/compiler/optimizing/induction_var_range.cc b/compiler/optimizing/induction_var_range.cc
index b162696a42..f9b6910acd 100644
--- a/compiler/optimizing/induction_var_range.cc
+++ b/compiler/optimizing/induction_var_range.cc
@@ -216,6 +216,14 @@ bool InductionVarRange::IsConstant(HInductionVarAnalysis::InductionInfo* info,
         }
       }
     } while (RefineOuter(&v_min, &v_max));
+    // Exploit array length + c >= c, with c <= 0 to avoid arithmetic wrap-around anomalies
+    // (e.g. array length == maxint and c == 1 would yield minint).
+    if (request == kAtLeast) {
+      if (v_min.a_constant == 1 && v_min.b_constant <= 0 && v_min.instruction->IsArrayLength()) {
+        *value = v_min.b_constant;
+        return true;
+      }
+    }
   }
   return false;
 }