Improve bound analysis on constant range.

Rationale:
A low hanging fruit basedon the first CL
that addressed b/70688025 (when the method
is inlined, BCE did not kick in due to
missing the now constant range).

Bug: b/70688025

Test: test-art-host test-art-target
Change-Id: Ic317d5a0920e654b5158694a1dfa1ea359e0a839

1 files changed, 17 insertions, 3 deletions

diff --git a/compiler/optimizing/bounds_check_elimination.cc b/compiler/optimizing/bounds_check_elimination.cc
index 147df1e3e8..d893cc88c4 100644
--- a/compiler/optimizing/bounds_check_elimination.cc
+++ b/compiler/optimizing/bounds_check_elimination.cc
@@ -836,9 +836,23 @@ class BCEVisitor : public HGraphVisitor {
       ValueRange array_range(&allocator_, lower, upper);
       // Try index range obtained by dominator-based analysis.
       ValueRange* index_range = LookupValueRange(index, block);
-      if (index_range != nullptr && index_range->FitsIn(&array_range)) {
-        ReplaceInstruction(bounds_check, index);
-        return;
+      if (index_range != nullptr) {
+        if (index_range->FitsIn(&array_range)) {
+          ReplaceInstruction(bounds_check, index);
+          return;
+        } else if (index_range->IsConstantValueRange()) {
+          // If the non-constant index turns out to have a constant range,
+          // make one more attempt to get a constant in the array range.
+          ValueRange* existing_range = LookupValueRange(array_length, block);
+          if (existing_range != nullptr &&
+              existing_range->IsConstantValueRange()) {
+            ValueRange constant_array_range(&allocator_, lower, existing_range->GetLower());
+            if (index_range->FitsIn(&constant_array_range)) {
+              ReplaceInstruction(bounds_check, index);
+              return;
+            }
+          }
+        }
       }
       // Try index range obtained by induction variable analysis.
       // Disables dynamic bce if OOB is certain.