optimizing: Fix undefined behavior in graph checker

Checking a variable being null after dereference is undefed behavior
and the null check is often optimized out.

Change-Id: I4d80510af6d49def1f9f7bd82c25eb366169babb

1 files changed, 10 insertions, 8 deletions

diff --git a/compiler/optimizing/graph_checker.cc b/compiler/optimizing/graph_checker.cc
index 6a140458a6..aea901dec7 100644
--- a/compiler/optimizing/graph_checker.cc
+++ b/compiler/optimizing/graph_checker.cc
@@ -338,19 +338,21 @@ void GraphChecker::VisitInstruction(HInstruction* instruction) {
 
   // Ensure the inputs of `instruction` are defined in a block of the graph.
   for (HInstruction* input : instruction->GetInputs()) {
-    const HInstructionList& list = input->IsPhi()
-        ? input->GetBlock()->GetPhis()
-        : input->GetBlock()->GetInstructions();
     if (input->GetBlock() == nullptr) {
       AddError(StringPrintf("Input %d of instruction %d is not in any "
                             "basic block of the control-flow graph.",
                             input->GetId(),
                             instruction->GetId()));
-    } else if (!list.Contains(input)) {
-      AddError(StringPrintf("Input %d of instruction %d is not defined "
-                            "in a basic block of the control-flow graph.",
-                            input->GetId(),
-                            instruction->GetId()));
+    } else {
+      const HInstructionList& list = input->IsPhi()
+          ? input->GetBlock()->GetPhis()
+          : input->GetBlock()->GetInstructions();
+      if (!list.Contains(input)) {
+        AddError(StringPrintf("Input %d of instruction %d is not defined "
+                              "in a basic block of the control-flow graph.",
+                              input->GetId(),
+                              instruction->GetId()));
+      }
     }
   }