From 11ea496dd81cad9f55c1b5b6def5833e4ed6f0b1 Mon Sep 17 00:00:00 2001
From: Alexander Markov <alexmarkov@google.com>
Date: Thu, 23 Jan 2025 11:41:00 -0800
Subject: [PATCH] [vm,dart2wasm,tfa] Handle 'Never' static type as unreachable
 in TFA

When building a data flow summary, break control and data flow after
invocations with static result type 'Never', expressing that code after
such invocation is unreachable.

TEST=pkg/vm/testcases/transformations/type_flow/summary_collector/control_flow.dart

Issue: https://github.com/dart-lang/sdk/issues/59941
Change-Id: I2e5acd861e4192bae231d356aeacf921a14766f5
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/405443
Reviewed-by: Slava Egorov <vegorov@google.com>
Commit-Queue: Alexander Markov <alexmarkov@google.com>
---
 .../type_flow/summary_collector.dart          | 28 +++++++++++++------
 .../summary_collector/control_flow.dart       | 11 ++++++++
 .../control_flow.dart.expect                  |  9 ++++++
 3 files changed, 39 insertions(+), 9 deletions(-)

diff --git a/pkg/vm/lib/transformations/type_flow/summary_collector.dart b/pkg/vm/lib/transformations/type_flow/summary_collector.dart
index 0411c7fb023c..e9bccf158591 100644
--- a/pkg/vm/lib/transformations/type_flow/summary_collector.dart
+++ b/pkg/vm/lib/transformations/type_flow/summary_collector.dart
@@ -1275,29 +1275,39 @@ class SummaryCollector extends RecursiveResultVisitor<TypeExpr?> {
     _declareVariable(decl, _typesBuilder.fromStaticType(decl.type, true));
   }
 
-  Call _makeCall(TreeNode node, Selector selector, Args<TypeExpr> args,
+  TypeExpr _makeCall(TreeNode node, Selector selector, Args<TypeExpr> args,
       {bool isInstanceCreation = false}) {
-    Type? staticResultType = null;
     Member? target;
     if (selector is DirectSelector) {
       target = selector.member;
     } else if (selector is InterfaceSelector) {
       target = selector.member;
     }
-    if (target is Procedure && node is Expression) {
-      final returnType = target.function.returnType;
+    Type? staticResultType = null;
+    if (node is Expression) {
       final staticDartType = _staticDartType(node);
-      // TODO(dartbug.com/54200): static type cannot be trusted when
-      // function type is returned.
-      if (returnType is TypeParameterType ||
-          (returnType != staticDartType && returnType is! FunctionType)) {
-        staticResultType = _typesBuilder.fromStaticType(staticDartType, true);
+      if (staticDartType is NeverType &&
+          staticDartType.declaredNullability == Nullability.nonNullable) {
+        staticResultType = emptyType;
+      } else if (target is Procedure) {
+        final returnType = target.function.returnType;
+        // TODO(dartbug.com/54200): static type cannot be trusted when
+        // function type is returned.
+        if (returnType is TypeParameterType ||
+            (returnType != staticDartType && returnType is! FunctionType)) {
+          staticResultType = _typesBuilder.fromStaticType(staticDartType, true);
+        }
       }
     }
     Call call = new Call(selector, args, staticResultType, isInstanceCreation);
     call.condition = _currentCondition;
     _summary.add(call);
     callSites[node] = call;
+    if (staticResultType is EmptyType) {
+      _currentCondition = emptyType;
+      _variableValues = _makeEmptyVariableValues();
+      return emptyType;
+    }
     return call;
   }
 
diff --git a/pkg/vm/testcases/transformations/type_flow/summary_collector/control_flow.dart b/pkg/vm/testcases/transformations/type_flow/summary_collector/control_flow.dart
index 89ffa3cc298e..d3886817f536 100644
--- a/pkg/vm/testcases/transformations/type_flow/summary_collector/control_flow.dart
+++ b/pkg/vm/testcases/transformations/type_flow/summary_collector/control_flow.dart
@@ -324,4 +324,15 @@ void cast1(x) {
   bar(x);
 }
 
+void never1(bool cond) {
+  int i = 1;
+  if (cond) {
+    i = 2;
+    returnNever();
+  }
+  foo(i);
+}
+
+Never returnNever() => throw 'bye';
+
 main() {}
diff --git a/pkg/vm/testcases/transformations/type_flow/summary_collector/control_flow.dart.expect b/pkg/vm/testcases/transformations/type_flow/summary_collector/control_flow.dart.expect
index 4a8ae46f6c8a..2f2da641d1b6 100644
--- a/pkg/vm/testcases/transformations/type_flow/summary_collector/control_flow.dart.expect
+++ b/pkg/vm/testcases/transformations/type_flow/summary_collector/control_flow.dart.expect
@@ -337,6 +337,15 @@ t1 = _TypeCheck (%x against #lib::C1) (for x as #lib::C1)
 t2 = _Call direct [#lib::foo] (t1)
 t3 = _Call direct [#lib::bar] (t1)
 RESULT: _T {}?
+------------ never1 ------------
+%cond = _Parameter #0 [_T (dart.core::bool)+]
+t1 = _Call direct [#lib::returnNever] () {%cond}
+t2 = Not (%cond)
+t3 = _Call direct [#lib::foo] (_T (dart.core::_Smi, 1)) {t2}
+RESULT: _T {}?
+------------ returnNever ------------
+
+RESULT: _T {}
 ------------ main ------------
 
 RESULT: _T {}?