[vm] Guard against double finalization from annotations on fields.

Bug: #37544
Change-Id: Ie3620dd9adf8382afc018cf764965b4ff74d2b75
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/109440
Reviewed-by: Alexander Markov <alexmarkov@google.com>
Commit-Queue: Ryan Macnak <rmacnak@google.com>

runtime/vm/compiler/backend/il_arm.cc

@@ -2486,6 +2486,7 @@ void StoreInstanceFieldInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
 
   const Register instance_reg = locs()->in(0).reg();
   const intptr_t offset_in_bytes = OffsetInBytes();
+  ASSERT(offset_in_bytes > 0);  // Field is finalized and points after header.
 
   if (IsUnboxedStore() && compiler->is_optimizing()) {
     const DRegister value = EvenDRegisterOf(locs()->in(1).fpu_reg());

runtime/vm/compiler/backend/il_arm64.cc

@@ -2156,6 +2156,7 @@ void StoreInstanceFieldInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
 
   const Register instance_reg = locs()->in(0).reg();
   const intptr_t offset_in_bytes = OffsetInBytes();
+  ASSERT(offset_in_bytes > 0);  // Field is finalized and points after header.
 
   if (IsUnboxedStore() && compiler->is_optimizing()) {
     const VRegister value = locs()->in(1).fpu_reg();

runtime/vm/compiler/backend/il_dbc.cc

@@ -1139,6 +1139,7 @@ EMIT_NATIVE_CODE(AllocateObject,
 }
 
 EMIT_NATIVE_CODE(StoreInstanceField, 2) {
+  ASSERT(OffsetInBytes() > 0);  // Field is finalized and points after header.
   ASSERT(OffsetInBytes() % kWordSize == 0);
   if (compiler->is_optimizing()) {
     const Register value = locs()->in(1).reg();

runtime/vm/compiler/backend/il_ia32.cc

@@ -2055,6 +2055,7 @@ void StoreInstanceFieldInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
 
   const Register instance_reg = locs()->in(0).reg();
   const intptr_t offset_in_bytes = OffsetInBytes();
+  ASSERT(offset_in_bytes > 0);  // Field is finalized and points after header.
 
   if (IsUnboxedStore() && compiler->is_optimizing()) {
     XmmRegister value = locs()->in(1).fpu_reg();

runtime/vm/compiler/backend/il_x64.cc

@@ -2171,6 +2171,7 @@ void StoreInstanceFieldInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
 
   const Register instance_reg = locs()->in(0).reg();
   const intptr_t offset_in_bytes = OffsetInBytes();
+  ASSERT(offset_in_bytes > 0);  // Field is finalized and points after header.
 
   if (IsUnboxedStore() && compiler->is_optimizing()) {
     XmmRegister value = locs()->in(1).fpu_reg();

runtime/vm/kernel_loader.cc

@@ -1575,6 +1575,13 @@ void KernelLoader::FinishClassLoading(const Class& klass,
           TokenPosition::kNoSource, TokenPosition::kNoSource);
       fields_.Add(&deleted_enum_sentinel);
     }
+
+    // Due to ReadVMAnnotations(), the klass may have been loaded at this point
+    // (loading the class while evaluating annotations).
+    if (klass.is_loaded()) {
+      return;
+    }
+
     klass.SetFields(Array::Handle(Z, MakeFieldsArray()));
   }