[CanonicalizeOSSALifetime] Swapped ignore meaning.

In various places, CanonicalizeOSSALifetime checks whether instructions
are "interesting enough to be worth hoisting over" for the purpose of
avoiding hoisting over instructions that would result in churning and
failing to find a fixed point when iterating in CopyPropagation.
Elsewhere, ::ignoredByDestroyHoisting is used.  Previously,
findDestroyOnCFGEdge used isIncidentalUse.  Replaced that useage with
::ignoredByDestroyHoisting.

Author: nate-chandler

lib/SILOptimizer/Utils/CanonicalOSSALifetime.cpp

@@ -411,12 +411,12 @@ void CanonicalizeOSSALifetime::extendLivenessThroughOverlappingAccess() {
 // liveness computed in Step 1.
 //===----------------------------------------------------------------------===//
 
-// Look past destroys and incidental uses to find a destroy on \p edgeBB that
+// Look past ignoreable instructions to find a destroy on \p edgeBB that
 // destroys \p def.
 static DestroyValueInst *findDestroyOnCFGEdge(SILBasicBlock *edgeBB,
                                               SILValue def) {
   for (auto &inst : *edgeBB) {
-    if (isIncidentalUse(&inst))
+    if (CanonicalizeOSSALifetime::ignoredByDestroyHoisting(inst.getKind()))
       continue;
     if (auto *destroy = dyn_cast<DestroyValueInst>(&inst)) {
       if (destroy->getOperand() == def)

test/SILOptimizer/lexical_destroy_folding.sil

@@ -574,8 +574,8 @@ exit:
 // CHECK:         [[COPY:%[^,]+]] = copy_value [[LIFETIME]]
 // CHECK:         cond_br undef, [[LEFT:bb[0-9]+]], [[RIGHT:bb[0-9]+]]
 // CHECK:       [[LEFT]]:
-// CHECK:         destroy_value [[COPY]]
 // CHECK:         [[CALLEE_OWNED:%[^,]+]] = function_ref @callee_owned
+// CHECK:         destroy_value [[COPY]]
 // CHECK:         end_borrow [[LIFETIME]]
 // CHECK:         apply [[CALLEE_OWNED]]([[MOVE]])
 // CHECK:         br [[EXIT:bb[0-9]+]]