Don't emit upcast to the same type in SimplifyAllocRefDynamic, add test, add comment

Author: kubamracek

SwiftCompilerSources/Sources/Optimizer/InstructionSimplification/SimplifyAllocRefDynamic.swift

@@ -26,20 +26,29 @@ extension AllocRefDynamicInst : OnoneSimplifyable {
     ///   %8 = (... some use of ...) %7 : $BaseClass
 
     let type: Type
+    let emitUpcast: Bool
     if let metatypeInst = metatypeOperand.value as? MetatypeInst {
       type = metatypeInst.type.loweredInstanceTypeOfMetatype(in: parentFunction)
+      emitUpcast = false
     } else if let upcastInst = metatypeOperand.value as? UpcastInst,
         let metatypeInst = upcastInst.operands[0].value as? MetatypeInst {
       type = metatypeInst.type.loweredInstanceTypeOfMetatype(in: parentFunction)
+      emitUpcast = true
     } else {
       return
     }
 
     let builder = Builder(before: self, context)
     let newAlloc = builder.createAllocRef(type, isObjC: self.isObjC, canAllocOnStack: self.canAllocOnStack, isBare: false,
       tailAllocatedTypes: self.tailAllocatedTypes, tailAllocatedCounts: Array(self.tailAllocatedCounts.values))
-    let newCast = builder.createUpcast(from: newAlloc, to: self.type)
-    uses.replaceAll(with: newCast, context)
+    
+    let result: Value
+    if emitUpcast {
+      result = builder.createUpcast(from: newAlloc, to: self.type)
+    } else {
+      result = newAlloc
+    }
+    uses.replaceAll(with: result, context)
     context.erase(instruction: self)
   }
 }

stdlib/public/core/ManagedBuffer.swift

@@ -78,6 +78,8 @@ extension ManagedBuffer where Element: ~Copyable {
   @_preInverseGenerics
   @inlinable
   #if $Embedded
+  // Transparent in Embedded Swift to avoid needing "self" as a metatype. By
+  // inlining into the caller, we'll know the concrete type instead.
   @_transparent
   #endif
   public final class func create(

test/SILOptimizer/simplify_alloc_ref_dynamic.sil

@@ -13,17 +13,16 @@ class SubClass: BaseClass {
   override init()
 }
 
-// CHECK-LABEL: sil [ossa] @test
+// CHECK-LABEL: sil [ossa] @test_alloc_ref_dynamic_with_upcast
 // CHECK:       bb0(%0 : $Int):
 // CHECK:         struct_extract %0 : $Int, #Int._value
 // CHECK:         builtin "truncOrBitCast_Int64_Word"({{.*}} : $Builtin.Int64) : $Builtin.Word
 // CHECK:         [[AL:%.*]] = alloc_ref [tail_elems $Int * {{.*}} : $Builtin.Word] $SubClass
 // CHECK:         [[UP:%.*]] = upcast [[AL]] : $SubClass to $BaseClass
 // CHECK:         [[MO:%.*]] = move_value [lexical] [var_decl] [[UP]] : $BaseClass
 // CHECK:         return [[MO]] : $BaseClass
-// CHECK:       } // end sil function 'test'
-sil [ossa] @test : $@convention(thin) (Int) -> @owned BaseClass {
-// %0 "minimumCapacity"
+// CHECK:       } // end sil function 'test_alloc_ref_dynamic_with_upcast'
+sil [ossa] @test_alloc_ref_dynamic_with_upcast : $@convention(thin) (Int) -> @owned BaseClass {
 bb0(%0 : $Int):
   %4 = metatype $@thick SubClass.Type
   %5 = upcast %4 : $@thick SubClass.Type to $@thick BaseClass.Type
@@ -33,3 +32,21 @@ bb0(%0 : $Int):
   %13 = move_value [lexical] [var_decl] %12 : $BaseClass
   return %13 : $BaseClass
 }
+
+// CHECK-LABEL: sil [ossa] @test_alloc_ref_dynamic_without_upcast
+// CHECK:       bb0(%0 : $Int):
+// CHECK:         struct_extract %0 : $Int, #Int._value
+// CHECK:         builtin "truncOrBitCast_Int64_Word"({{.*}} : $Builtin.Int64) : $Builtin.Word
+// CHECK:         [[AL:%.*]] = alloc_ref [tail_elems $Int * {{.*}} : $Builtin.Word] $BaseClass
+// CHECK:         [[MO:%.*]] = move_value [lexical] [var_decl] [[AL]] : $BaseClass
+// CHECK:         return [[MO]] : $BaseClass
+// CHECK:       } // end sil function 'test_alloc_ref_dynamic_without_upcast'
+sil [ossa] @test_alloc_ref_dynamic_without_upcast : $@convention(thin) (Int) -> @owned BaseClass {
+bb0(%0 : $Int):
+  %4 = metatype $@thick BaseClass.Type
+  %10 = struct_extract %0 : $Int, #Int._value
+  %11 = builtin "truncOrBitCast_Int64_Word"(%10 : $Builtin.Int64) : $Builtin.Word
+  %12 = alloc_ref_dynamic [tail_elems $Int * %11 : $Builtin.Word] %4 : $@thick BaseClass.Type, $BaseClass
+  %13 = move_value [lexical] [var_decl] %12 : $BaseClass
+  return %13 : $BaseClass
+}