[OwnedLifetimeCan] Fix clearing.

Just clear all structures in a single method which is called wherever
clearing is done.  Fixes a failure to clear discoveredBlocks under
certain circumstances.

Author: nate-chandler

include/swift/SILOptimizer/Utils/CanonicalizeOSSALifetime.h

@@ -342,11 +342,7 @@ class CanonicalizeOSSALifetime final {
   void initializeLiveness(SILValue def,
                           ArrayRef<SILInstruction *> lexicalLifetimeEnds) {
     assert(consumingBlocks.empty() && debugValues.empty());
-    // Clear the cached analysis pointer just in case the client invalidates the
-    // analysis, freeing its memory.
-    accessBlocks = nullptr;
-    consumes.clear();
-    destroys.clear();
+    clear();
 
     currentDef = def;
     currentLexicalLifetimeEnds = lexicalLifetimeEnds;
@@ -358,9 +354,18 @@ class CanonicalizeOSSALifetime final {
   }
 
   void clear() {
+    // Clear the access blocks analysis pointer in case the client invalidates
+    // the analysis.  If the client did, the analysis will be recomputed in
+    // extendLivenessThroughOverlappingAccess; if it didn't, the analysis
+    // pointer will just be set back to its old value when the analysis' cache
+    // is consulted in extendLivenessThroughOverlappingAccess.
+    accessBlocks = nullptr;
+
     consumingBlocks.clear();
     debugValues.clear();
     discoveredBlocks.clear();
+    consumes.clear();
+    destroys.clear();
   }
 
   /// Top-Level API: rewrites copies and destroys within \p def's extended

lib/SILOptimizer/Utils/CanonicalizeOSSALifetime.cpp

@@ -1241,7 +1241,6 @@ void CanonicalizeOSSALifetime::rewriteLifetimes() {
   rewriteCopies();
 
   clear();
-  consumes.clear();
 }
 
 /// Canonicalize a single extended owned lifetime.