Make HloDataFlowAnalysis updatable after transforming the HLO graph.

Updating is possible if operands/uses or computation roots change in
the graph. Updating is not possible if instructions are deleted or if
new instructions are added.

Specific changes:
* Add verification methods for asserting invariants and checking the
  analysis after updating.
* Always add phi values at while instructions. Previously these were
  added only if the phi had different inputs. The advantage of using
  phi's unconditionally is that the set of values is fixed for a
  module. Updates due to changing operands/uses in the graph do not
  create new values.
* Store values in a vector rather than a map. With unconditional phi
  values, the number of HloValues is fixed so the values can be held
  in a vector with stable references to elements.

PiperOrigin-RevId: 164778750

1 files changed, 1 insertions, 1 deletions

diff --git a/tensorflow/compiler/xla/service/hlo_computation.h b/tensorflow/compiler/xla/service/hlo_computation.h
index 4827fce08a..5f651060fd 100644
--- a/tensorflow/compiler/xla/service/hlo_computation.h
+++ b/tensorflow/compiler/xla/service/hlo_computation.h
@@ -161,7 +161,7 @@ class HloComputation {
   // reachability. Trivially an instruction is reachable from itself.
   std::unique_ptr<HloReachabilityMap> ComputeReachability() const;
 
-  // Updates the given reachabilty map after the immediate predecessor set
+  // Updates the given reachability map after the immediate predecessor set
   // (operands and control predecessors) of 'instruction' has changed.
   void UpdateReachabilityThroughInstruction(
       const HloInstruction* instruction, HloReachabilityMap* reachability_map);