[lldb][ClangASTImporter] Import record layouts from origin if available (llvm#83295)

Layout information for a record gets stored in the `ClangASTImporter`
associated with the `DWARFASTParserClang` that originally parsed the
record. LLDB sometimes moves clang types from one AST to another (in the
reproducer the origin AST was a precompiled-header and the destination
was the AST backing the executable). When clang then asks LLDB to
`layoutRecordType`, it will do so with the help of the
`ClangASTImporter` the type is associated with. If the type's origin is
actually in a different LLDB module (and thus a different
`DWARFASTParserClang` was used to set its layout info), we won't find
the layout info in our local `ClangASTImporter`.

In the reproducer this meant we would drop the alignment info of the
origin type and misread a variable's contents with `frame var` and
`expr`.

There is logic in `ClangASTSource::layoutRecordType` to import an
origin's layout info. This patch re-uses that infrastructure to import
an origin's layout from one `ClangASTImporter` instance to another.

rdar://123274144
(cherry picked from commit 07ffb7e)

Author: Michael137

lldb/source/Plugins/ExpressionParser/Clang/ClangASTImporter.cpp

@@ -777,7 +777,6 @@ bool ClangASTImporter::LayoutRecordType(
 
   RecordDeclToLayoutMap::iterator pos =
       m_record_decl_to_layout_map.find(record_decl);
-  bool success = false;
   base_offsets.clear();
   vbase_offsets.clear();
   if (pos != m_record_decl_to_layout_map.end()) {
@@ -786,13 +785,22 @@ bool ClangASTImporter::LayoutRecordType(
     field_offsets.swap(pos->second.field_offsets);
     base_offsets.swap(pos->second.base_offsets);
     vbase_offsets.swap(pos->second.vbase_offsets);
-    success = true;
-  } else {
-    bit_size = 0;
-    alignment = 0;
-    field_offsets.clear();
   }
-  return success;
+
+  // It's possible that we calculated the layout in a different
+  // ClangASTImporter instance. Try to import such layout if
+  // our decl has an origin.
+  if (auto origin = GetDeclOrigin(record_decl); origin.Valid())
+    if (importRecordLayoutFromOrigin(record_decl, bit_size, alignment,
+                                     field_offsets, base_offsets,
+                                     vbase_offsets))
+      return true;
+
+  bit_size = 0;
+  alignment = 0;
+  field_offsets.clear();
+
+  return false;
 }
 
 void ClangASTImporter::SetRecordLayout(clang::RecordDecl *decl,

lldb/test/API/lang/cpp/gmodules/alignment/Makefile

@@ -0,0 +1,4 @@
+PCH_CXX_SOURCE = pch.h
+CXX_SOURCES = main.cpp
+
+include Makefile.rules

lldb/test/API/lang/cpp/gmodules/alignment/TestPchAlignment.py

@@ -0,0 +1,60 @@
+"""
+Tests that we correctly track AST layout info
+(specifically alignment) when moving AST nodes
+between ClangASTImporter instances (in this case,
+from pch to executable to expression AST).
+"""
+
+import lldb
+import os
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+
+class TestPchAlignment(TestBase):
+    @add_test_categories(["gmodules"])
+    def test_expr(self):
+        self.build()
+        lldbutil.run_to_source_breakpoint(
+            self, "return data", lldb.SBFileSpec("main.cpp")
+        )
+
+        self.expect(
+            "frame variable data",
+            substrs=["row = 1", "col = 2", "row = 3", "col = 4", "stride = 5"],
+        )
+
+    @add_test_categories(["gmodules"])
+    def test_frame_var(self):
+        self.build()
+        lldbutil.run_to_source_breakpoint(
+            self, "return data", lldb.SBFileSpec("main.cpp")
+        )
+
+        self.expect_expr(
+            "data",
+            result_type="MatrixData",
+            result_children=[
+                ValueCheck(
+                    name="section",
+                    children=[
+                        ValueCheck(
+                            name="origin",
+                            children=[
+                                ValueCheck(name="row", value="1"),
+                                ValueCheck(name="col", value="2"),
+                            ],
+                        ),
+                        ValueCheck(
+                            name="size",
+                            children=[
+                                ValueCheck(name="row", value="3"),
+                                ValueCheck(name="col", value="4"),
+                            ],
+                        ),
+                    ],
+                ),
+                ValueCheck(name="stride", value="5"),
+            ],
+        )

lldb/test/API/lang/cpp/gmodules/alignment/main.cpp

@@ -0,0 +1,10 @@
+int main(int argc, const char *argv[]) {
+  struct MatrixData data = {0};
+  data.section.origin.row = 1;
+  data.section.origin.col = 2;
+  data.section.size.row = 3;
+  data.section.size.col = 4;
+  data.stride = 5;
+
+  return data.section.size.row;
+}

lldb/test/API/lang/cpp/gmodules/alignment/pch.h

@@ -0,0 +1,21 @@
+#ifndef PCH_H_IN
+#define PCH_H_IN
+
+static const int kAlignment = 64;
+
+struct [[gnu::aligned(kAlignment)]] RowCol {
+  unsigned row;
+  unsigned col;
+};
+
+struct [[gnu::aligned(kAlignment)]] Submatrix {
+  struct RowCol origin;
+  struct RowCol size;
+};
+
+struct [[gnu::aligned(kAlignment)]] MatrixData {
+  struct Submatrix section;
+  unsigned stride;
+};
+
+#endif // _H_IN