[SSADestroyHoisting] Expand store [assign]s first.

To create more opportunities for hoisting.

Author: nate-chandler

lib/SILOptimizer/Transforms/SSADestroyHoisting.cpp

@@ -565,6 +565,7 @@ void SSADestroyHoisting::run() {
 
   llvm::SmallVector<AllocStackInst *, 4> asis;
   llvm::SmallVector<BeginAccessInst *, 4> bais;
+  llvm::SmallVector<StoreInst *, 4> sis;
 
   // Collect the instructions that we'll be transforming.
   for (auto &block : *getFunction()) {
@@ -575,10 +576,32 @@ void SSADestroyHoisting::run() {
         if (bai->getAccessKind() == SILAccessKind::Modify) {
           bais.push_back(bai);
         }
+      } else if (auto *si = dyn_cast<StoreInst>(&inst)) {
+        if (si->getOwnershipQualifier() == StoreOwnershipQualifier::Assign) {
+          sis.push_back(si);
+        }
       }
     }
   }
 
+  // Before hoisting, expand all
+  //
+  //     store [assign]
+  //
+  // instructions into
+  //
+  //     destroy_addr
+  //     store [init]
+  //
+  // sequences to create more destroy_addrs to hoist.
+  for (auto *si : sis) {
+    auto builder = SILBuilderWithScope(si);
+    builder.createDestroyAddr(
+        RegularLocation::getAutoGeneratedLocation(si->getLoc()),
+        si->getOperand(1));
+    si->setOwnershipQualifier(StoreOwnershipQualifier::Init);
+  }
+
   // We assume that the function is in reverse post order so visiting the
   // blocks and pushing begin_access as we see them and then popping them off
   // the end will result in hoisting inner begin_access' destroy_addrs first.