AliasAnalysis: compute more precise memory behavior for debug_value undef and the prepareInitialization and zeroInitializer builtins

Author: eeckstein

SwiftCompilerSources/Sources/Optimizer/Analysis/AliasAnalysis.swift

@@ -327,7 +327,8 @@ struct AliasAnalysis {
       return defaultEffects(of: endBorrow, on: memLoc)
 
     case let debugValue as DebugValueInst:
-      if debugValue.operand.value.type.isAddress && memLoc.mayAlias(with: debugValue.operand.value, self) {
+      let v = debugValue.operand.value
+      if v.type.isAddress, !(v is Undef), memLoc.mayAlias(with: v, self) {
         return .init(read: true)
       } else {
         return .noEffects
@@ -434,6 +435,11 @@ struct AliasAnalysis {
       }
       let callee = builtin.operands[1].value
       return context.calleeAnalysis.getSideEffects(ofCallee: callee).memory
+    case .PrepareInitialization, .ZeroInitializer:
+      if builtin.arguments.count == 1, memLoc.mayAlias(with: builtin.arguments[0], self) {
+        return .init(write: true)
+      }
+      return .noEffects
     default:
       return defaultEffects(of: builtin, on: memLoc)
     }

test/SILOptimizer/mem-behavior.sil

@@ -1250,11 +1250,16 @@ bb0(%0 : $Builtin.RawPointer):
 // CHECK-NEXT:      debug_value %0 : $*Int, let, name "x"
 // CHECK-NEXT:      %1 = alloc_stack $Int
 // CHECK-NEXT:    r=0,w=0
+// CHECK:       PAIR #2.
+// CHECK-NEXT:      debug_value undef : $*Int, let, name "y"
+// CHECK-NEXT:      %0 = alloc_stack $Int
+// CHECK-NEXT:    r=0,w=0
 sil @test_debug_value : $@convention(thin) () -> () {
 bb0:
   %0 = alloc_stack $Int
   %1 = alloc_stack $Int
   debug_value %0 : $*Int, let, name "x"
+  debug_value undef : $*Int, let, name "y"
   dealloc_stack %1 : $*Int
   dealloc_stack %0 : $*Int
   %r = tuple ()
@@ -1435,6 +1440,34 @@ bb0:
   return %5 : $()
 }
 
+// CHECK-LABEL: @builtin_initializer_and_class
+// CHECK:       PAIR #0.
+// CHECK-NEXT:      %3 = builtin "zeroInitializer"(%2 : $*Int32) : $()
+// CHECK-NEXT:      %1 = ref_element_addr %0 : $C, #C.prop
+// CHECK-NEXT:    r=0,w=0
+// CHECK:       PAIR #1.
+// CHECK-NEXT:      %3 = builtin "zeroInitializer"(%2 : $*Int32) : $()
+// CHECK-NEXT:      %2 = alloc_stack $Int32
+// CHECK-NEXT:    r=0,w=1
+// CHECK:       PAIR #2.
+// CHECK-NEXT:      %4 = builtin "prepareInitialization"(%2 : $*Int32) : $()
+// CHECK-NEXT:      %1 = ref_element_addr %0 : $C, #C.prop
+// CHECK-NEXT:    r=0,w=0
+// CHECK:       PAIR #3.
+// CHECK-NEXT:      %4 = builtin "prepareInitialization"(%2 : $*Int32) : $()
+// CHECK-NEXT:      %2 = alloc_stack $Int32
+// CHECK-NEXT:    r=0,w=1
+sil @builtin_initializer_and_class : $@convention(thin) (@guaranteed C) -> () {
+bb0(%0 : $C):
+  %1 = ref_element_addr %0, #C.prop
+  %2 = alloc_stack $Int32
+  %3 = builtin "zeroInitializer"(%2 : $*Int32) : $()
+  %4 = builtin "prepareInitialization"(%2 : $*Int32) : $()
+  dealloc_stack %2
+  %6 = tuple ()
+  return %6
+}
+
 // CHECK-LABEL: @test_stored_pointer
 // CHECK:       PAIR #2.
 // CHECK-NEXT:      %5 = apply %4(%2) : $@convention(thin) (@in Builtin.RawPointer) -> ()