[CanonicalizeOSSALifetime] Renamed member.

The member just clears the values.  After it adopted BitfieldRef, the
call to invalidate on the liveness instance was already superfluous.

(cherry picked from commit 3c4275a)

Author: nate-chandler

include/swift/SILOptimizer/Utils/CanonicalizeOSSALifetime.h

@@ -319,10 +319,9 @@ class CanonicalizeOSSALifetime final {
     liveness->initializeDef(getCurrentDef());
   }
 
-  void invalidateLiveness() {
+  void clear() {
     consumingBlocks.clear();
     debugValues.clear();
-    liveness->invalidate();
     discoveredBlocks.clear();
   }
 

lib/SILOptimizer/Utils/CanonicalizeOSSALifetime.cpp

@@ -1042,7 +1042,7 @@ bool CanonicalizeOSSALifetime::computeLiveness() {
   // Step 1: compute liveness
   if (!computeCanonicalLiveness()) {
     LLVM_DEBUG(llvm::errs() << "Failed to compute canonical liveness?!\n");
-    invalidateLiveness();
+    clear();
     return false;
   }
   if (accessBlockAnalysis) {
@@ -1076,7 +1076,7 @@ void CanonicalizeOSSALifetime::rewriteLifetimes() {
   // Step 6: rewrite copies and delete extra destroys
   rewriteCopies();
 
-  invalidateLiveness();
+  clear();
   consumes.clear();
 }