ART: Remove incorrect HFakeString optimization

Simplification of HFakeString assumes that it cannot be used until
String.<init> is called which is not true and causes different
behaviour between the compiler and the interpreter. This patch
removes the optimization together with the HFakeString instruction.

Instead, HNewInstance is generated and an empty String allocated
until it is replaced with the result of the StringFactory call. This
is consistent with the behaviour of the interpreter but is too
conservative. A follow-up CL will attempt to optimize out the initial
allocation when possible.

Bug: 26457745
Bug: 26486014

Change-Id: I7139e37ed00a880715bfc234896a930fde670c44

1 files changed, 28 insertions, 0 deletions

diff --git a/compiler/optimizing/graph_checker.cc b/compiler/optimizing/graph_checker.cc
index 6d0bdbe19b..2fe5b07b19 100644
--- a/compiler/optimizing/graph_checker.cc
+++ b/compiler/optimizing/graph_checker.cc
@@ -606,6 +606,34 @@ void SSAChecker::VisitInstruction(HInstruction* instruction) {
                             instruction->GetId()));
     }
   }
+
+  if (instruction->CanThrowIntoCatchBlock()) {
+    // Find the top-level environment. This corresponds to the environment of
+    // the catch block since we do not inline methods with try/catch.
+    HEnvironment* environment = instruction->GetEnvironment();
+    while (environment->GetParent() != nullptr) {
+      environment = environment->GetParent();
+    }
+
+    // Find all catch blocks and test that `instruction` has an environment
+    // value for each one.
+    const HTryBoundary& entry = instruction->GetBlock()->GetTryCatchInformation()->GetTryEntry();
+    for (HBasicBlock* catch_block : entry.GetExceptionHandlers()) {
+      for (HInstructionIterator phi_it(catch_block->GetPhis()); !phi_it.Done(); phi_it.Advance()) {
+        HPhi* catch_phi = phi_it.Current()->AsPhi();
+        if (environment->GetInstructionAt(catch_phi->GetRegNumber()) == nullptr) {
+          AddError(StringPrintf("Instruction %s:%d throws into catch block %d "
+                                "with catch phi %d for vreg %d but its "
+                                "corresponding environment slot is empty.",
+                                instruction->DebugName(),
+                                instruction->GetId(),
+                                catch_block->GetBlockId(),
+                                catch_phi->GetId(),
+                                catch_phi->GetRegNumber()));
+        }
+      }
+    }
+  }
 }
 
 static Primitive::Type PrimitiveKind(Primitive::Type type) {