TempRValueElimination: allow elimination of dead alloc_stacks in non-OSSA

Author: eeckstein

SwiftCompilerSources/Sources/Optimizer/FunctionPasses/TempRValueElimination.swift

@@ -160,7 +160,11 @@ private func getRemovableAllocStackDestination(
   //   %x = load %allocStack   // looks like a load, but is a `load [take]`
   //   strong_release %x
   // ```
-  guard copy.parentFunction.hasOwnership || allocStack.isDestroyedOnAllPaths(context) else {
+  guard copy.parentFunction.hasOwnership ||
+        allocStack.isDestroyedOnAllPaths(context) ||
+        // We can easily remove a dead alloc_stack
+        allocStack.uses.ignore(user: copy).ignore(usersOfType: DeallocStackInst.self).isEmpty
+  else {
     return nil
   }
 

test/IRGen/existentials_opaque_boxed.sil

@@ -1,4 +1,4 @@
-// RUN: %target-swift-frontend -disable-type-layout %s -emit-ir | %FileCheck %s -check-prefix=CHECK -check-prefix=CHECK-%target-ptrsize -DINT=i%target-ptrsize --check-prefix=CHECK-%target-cpu
+// RUN: %target-swift-frontend -Xllvm -sil-disable-pass=mandatory-temp-rvalue-elimination -disable-type-layout %s -emit-ir | %FileCheck %s -check-prefix=CHECK -check-prefix=CHECK-%target-ptrsize -DINT=i%target-ptrsize --check-prefix=CHECK-%target-cpu
 
 sil_stage canonical
 

test/IRGen/outlined_copy_addr.sil

@@ -1,6 +1,6 @@
 // RUN: %empty-directory(%t)
-// RUN: %target-swift-frontend -emit-module -enable-library-evolution -emit-module-path=%t/resilient_struct.swiftmodule -module-name=resilient_struct %S/../Inputs/resilient_struct.swift
-// RUN: %target-swift-frontend -emit-ir %s -I %t | %FileCheck %s
+// RUN: %target-swift-frontend -emit-module -Xllvm -sil-disable-pass=mandatory-temp-rvalue-elimination -enable-library-evolution -emit-module-path=%t/resilient_struct.swiftmodule -module-name=resilient_struct %S/../Inputs/resilient_struct.swift
+// RUN: %target-swift-frontend -Xllvm -sil-disable-pass=mandatory-temp-rvalue-elimination -emit-ir %s -I %t | %FileCheck %s
 
 import Swift
 import resilient_struct

test/SILOptimizer/temp_rvalue_opt.sil

@@ -29,6 +29,9 @@ class C {
   @_hasStorage let x: String
 }
 
+struct NC: ~Copyable {
+  var i: Int
+}
 
 sil @unknown : $@convention(thin) () -> ()
 sil @load_string : $@convention(thin) (@in_guaranteed String) -> String
@@ -842,3 +845,16 @@ bb0(%0 : $*Klass):
   return %4
 }
 
+// CHECK-LABEL: sil @dead_alloc_stack :
+// CHECK:       bb0(%0 : $*NC):
+// CHECK-NEXT:    tuple
+// CHECK-LABEL: } // end sil function 'dead_alloc_stack'
+sil @dead_alloc_stack : $@convention(thin) (@in NC) -> () {
+bb0(%0 : $*NC):
+  %1 = alloc_stack $NC
+  copy_addr [take] %0 to [init] %1
+  dealloc_stack %1
+  %r = tuple ()
+  return %r
+}
+