[Lldb-commits] [lldb] [lldb] Update the calling convention of BytecodeSyntheticChildren (PR #182155)

[via lldb-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-lldb

Author: Dave Lee (kastiglione)

<details>
<summary>Changes</summary>

This changes how "self" is constructed, where "self" is the data placed on the stack before calls to `num_children`, `get_child_at_index`, etc.

First, the return value of `init` is saved to its own member, `m_init_results`. Likewise, the return value of `update` is saved to a separate member, `m_update_results`.

Calls to both `init` and `update` recieve only the value object on their stack. This is done to simplify implementations of `update`. It makes them more "pure", in that the argument is always a single value (the value object). Previously `update` was called with the value of "self", which was shared between `init` and `update`, and was mutated by `update`.

Lastly, the results of `init` and `update` are concatenated to being the value of "self" when calling other methods.


---
Full diff: https://github.com/llvm/llvm-project/pull/182155.diff


2 Files Affected:

- (modified) lldb/include/lldb/DataFormatters/TypeSynthetic.h (+9-1) 
- (modified) lldb/source/DataFormatters/TypeSynthetic.cpp (+20-10) 


``````````diff
diff --git a/lldb/include/lldb/DataFormatters/TypeSynthetic.h b/lldb/include/lldb/DataFormatters/TypeSynthetic.h
index fbf1d060a92b2..ae51ab400ba3d 100644
--- a/lldb/include/lldb/DataFormatters/TypeSynthetic.h
+++ b/lldb/include/lldb/DataFormatters/TypeSynthetic.h
@@ -502,9 +502,17 @@ class BytecodeSyntheticChildren : public SyntheticChildren {
     lldb::ValueObjectSP GetChildAtIndex(uint32_t idx) override;
     llvm::Expected<size_t> GetIndexOfChildWithName(ConstString name) override;
 
+  private:
+    /// The data stack representing "self". The value of "self" is the results
+    /// of `init` combined with the results of `update`. Together, these values
+    /// are placed on the stack when calling `num_children`,
+    /// `get_child_at_index`, etc.
+    FormatterBytecode::DataStack GetSelf();
+
   private:
     const SyntheticBytecodeImplementation &m_impl;
-    FormatterBytecode::DataStack m_self;
+    FormatterBytecode::DataStack m_init_results;
+    FormatterBytecode::DataStack m_update_results;
   };
 
 public:
diff --git a/lldb/source/DataFormatters/TypeSynthetic.cpp b/lldb/source/DataFormatters/TypeSynthetic.cpp
index 10655cdca6f05..6e5721f357c6a 100644
--- a/lldb/source/DataFormatters/TypeSynthetic.cpp
+++ b/lldb/source/DataFormatters/TypeSynthetic.cpp
@@ -20,8 +20,10 @@
 #include "lldb/Symbol/CompilerType.h"
 #include "lldb/Target/Target.h"
 #include "lldb/Utility/StreamString.h"
+#include "llvm/ADT/STLExtras.h"
 #include "llvm/Support/Error.h"
 #include <cstdint>
+#include <iterator>
 
 using namespace lldb;
 using namespace lldb_private;
@@ -258,13 +260,11 @@ std::string ScriptedSyntheticChildren::GetDescription() {
 BytecodeSyntheticChildren::FrontEnd::FrontEnd(
     ValueObject &backend, SyntheticBytecodeImplementation &impl)
     : SyntheticChildrenFrontEnd(backend), m_impl(impl) {
-  FormatterBytecode::DataStack data(backend.GetSP());
-  if (!m_impl.init) {
-    m_self = std::move(data);
+  if (!m_impl.init)
     return;
-  }
 
   FormatterBytecode::ControlStack control = {m_impl.init->getBuffer()};
+  FormatterBytecode::DataStack data = {backend.GetSP()};
   llvm::Error error =
       FormatterBytecode::Interpret(control, data, FormatterBytecode::sig_init);
   if (error) {
@@ -274,7 +274,7 @@ BytecodeSyntheticChildren::FrontEnd::FrontEnd(
   }
 
   if (data.size() > 0)
-    m_self = std::move(data);
+    m_init_results = std::move(data);
 }
 
 lldb::ChildCacheState BytecodeSyntheticChildren::FrontEnd::Update() {
@@ -282,7 +282,7 @@ lldb::ChildCacheState BytecodeSyntheticChildren::FrontEnd::Update() {
     return ChildCacheState::eRefetch;
 
   FormatterBytecode::ControlStack control = {m_impl.update->getBuffer()};
-  FormatterBytecode::DataStack data = m_self;
+  FormatterBytecode::DataStack data = {m_backend.GetSP()};
   llvm::Error error = FormatterBytecode::Interpret(
       control, data, FormatterBytecode::sig_update);
   if (error) {
@@ -292,7 +292,7 @@ lldb::ChildCacheState BytecodeSyntheticChildren::FrontEnd::Update() {
   }
 
   if (data.size() > 0)
-    m_self = std::move(data);
+    m_update_results = std::move(data);
 
   return ChildCacheState::eRefetch;
 }
@@ -303,7 +303,7 @@ BytecodeSyntheticChildren::FrontEnd::CalculateNumChildren() {
     return 0;
 
   FormatterBytecode::ControlStack control = {m_impl.num_children->getBuffer()};
-  FormatterBytecode::DataStack data = m_self;
+  FormatterBytecode::DataStack data = GetSelf();
   llvm::Error error = FormatterBytecode::Interpret(
       control, data, FormatterBytecode::sig_get_num_children);
   if (error)
@@ -335,7 +335,7 @@ BytecodeSyntheticChildren::FrontEnd::GetChildAtIndex(uint32_t idx) {
 
   FormatterBytecode::ControlStack control = {
       m_impl.get_child_at_index->getBuffer()};
-  FormatterBytecode::DataStack data = m_self;
+  FormatterBytecode::DataStack data = GetSelf();
   data.emplace_back((uint64_t)idx);
   llvm::Error error = FormatterBytecode::Interpret(
       control, data, FormatterBytecode::sig_get_child_at_index);
@@ -365,7 +365,7 @@ BytecodeSyntheticChildren::FrontEnd::GetIndexOfChildWithName(ConstString name) {
 
   FormatterBytecode::ControlStack control = {
       m_impl.get_child_index->getBuffer()};
-  FormatterBytecode::DataStack data = m_self;
+  FormatterBytecode::DataStack data = GetSelf();
   data.emplace_back(name.GetString());
   llvm::Error error = FormatterBytecode::Interpret(
       control, data, FormatterBytecode::sig_get_child_index);
@@ -391,6 +391,16 @@ BytecodeSyntheticChildren::FrontEnd::GetIndexOfChildWithName(ConstString name) {
   return llvm::createStringError("@get_child_index returned invalid value");
 }
 
+FormatterBytecode::DataStack BytecodeSyntheticChildren::FrontEnd::GetSelf() {
+  FormatterBytecode::DataStack self;
+  llvm::copy(m_init_results, std::back_inserter(self));
+  llvm::copy(m_update_results, std::back_inserter(self));
+  if (self.empty())
+    // As a fallback, "self" is just the valobj.
+    self.emplace_back(m_backend.GetSP());
+  return self;
+}
+
 std::string BytecodeSyntheticChildren::GetDescription() {
   StreamString sstr;
   sstr.Printf("%s%s%s Bytecode synthetic", Cascades() ? "" : " (not cascading)",

``````````

</details>


https://github.com/llvm/llvm-project/pull/182155