[clang] [lldb] [clang][lldb] Don't assert structure layout correctness for layouts provided by LLDB (PR #93809)
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Thu May 30 04:51:54 PDT 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clang-codegen
Author: Michael Buch (Michael137)
<details>
<summary>Changes</summary>
This is the outcome of the discussions we had in
https://discourse.llvm.org/t/rfc-lldb-handling-no-unique-address-in-lldb/77483
To summarize, LLDB creates AST nodes by parsing debug-info and hands those off to Clang for codegen. There are certain Clang attributes that affect structure layout which are not encoded in DWARF, one of which is `[[no_unique_address]]`. But the affects of such attributes *is* encoded in DWARF in terms of member offsets and sizes. So some of the correctness checks that the `RecordLayoutBuilder` performs aren't really necessary for layouts provided by LLDB since we know that the offsets we get from DWARF are correct (modulo corrupt DWARF). Hence this patch guards those asserts behind the `DebuggerSupport` flag.
This unblocks the libc++ `compressed_pair` refactor in https://github.com/llvm/llvm-project/issues/93069
---
Full diff: https://github.com/llvm/llvm-project/pull/93809.diff
4 Files Affected:
- (modified) clang/lib/CodeGen/CGRecordLayoutBuilder.cpp (+12-6)
- (added) lldb/test/API/lang/cpp/no_unique_address/Makefile (+3)
- (added) lldb/test/API/lang/cpp/no_unique_address/TestNoUniqueAddress.py (+50)
- (added) lldb/test/API/lang/cpp/no_unique_address/main.cpp (+35)
``````````diff
diff --git a/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp b/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp
index 5169be204c14d..32fb032214e28 100644
--- a/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp
+++ b/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp
@@ -950,6 +950,9 @@ void CGRecordLowering::calculateZeroInit() {
// Verify accumulateBitfields computed the correct storage representations.
void CGRecordLowering::checkBitfieldClipping(bool IsNonVirtualBaseType) const {
#ifndef NDEBUG
+ if (Context.getLangOpts().DebuggerSupport)
+ return;
+
auto ScissorOffset = calculateTailClippingOffset(IsNonVirtualBaseType);
auto Tail = CharUnits::Zero();
for (const auto &M : Members) {
@@ -1008,7 +1011,8 @@ void CGRecordLowering::insertPadding() {
if (!Member->Data)
continue;
CharUnits Offset = Member->Offset;
- assert(Offset >= Size);
+ if (!Context.getLangOpts().DebuggerSupport)
+ assert(Offset >= Size);
// Insert padding if we need to.
if (Offset !=
Size.alignTo(Packed ? CharUnits::One() : getAlignment(Member->Data)))
@@ -1138,8 +1142,9 @@ CodeGenTypes::ComputeRecordLayout(const RecordDecl *D, llvm::StructType *Ty) {
const ASTRecordLayout &Layout = getContext().getASTRecordLayout(D);
uint64_t TypeSizeInBits = getContext().toBits(Layout.getSize());
- assert(TypeSizeInBits == getDataLayout().getTypeAllocSizeInBits(Ty) &&
- "Type size mismatch!");
+ if (!Context.getLangOpts().DebuggerSupport)
+ assert(TypeSizeInBits == getDataLayout().getTypeAllocSizeInBits(Ty) &&
+ "Type size mismatch!");
if (BaseTy) {
CharUnits NonVirtualSize = Layout.getNonVirtualSize();
@@ -1147,9 +1152,10 @@ CodeGenTypes::ComputeRecordLayout(const RecordDecl *D, llvm::StructType *Ty) {
uint64_t AlignedNonVirtualTypeSizeInBits =
getContext().toBits(NonVirtualSize);
- assert(AlignedNonVirtualTypeSizeInBits ==
- getDataLayout().getTypeAllocSizeInBits(BaseTy) &&
- "Type size mismatch!");
+ if (!Context.getLangOpts().DebuggerSupport)
+ assert(AlignedNonVirtualTypeSizeInBits ==
+ getDataLayout().getTypeAllocSizeInBits(BaseTy) &&
+ "Type size mismatch!");
}
// Verify that the LLVM and AST field offsets agree.
diff --git a/lldb/test/API/lang/cpp/no_unique_address/Makefile b/lldb/test/API/lang/cpp/no_unique_address/Makefile
new file mode 100644
index 0000000000000..99998b20bcb05
--- /dev/null
+++ b/lldb/test/API/lang/cpp/no_unique_address/Makefile
@@ -0,0 +1,3 @@
+CXX_SOURCES := main.cpp
+
+include Makefile.rules
diff --git a/lldb/test/API/lang/cpp/no_unique_address/TestNoUniqueAddress.py b/lldb/test/API/lang/cpp/no_unique_address/TestNoUniqueAddress.py
new file mode 100644
index 0000000000000..373bcb9062cde
--- /dev/null
+++ b/lldb/test/API/lang/cpp/no_unique_address/TestNoUniqueAddress.py
@@ -0,0 +1,50 @@
+"""
+Test that LLDB correctly handles fields
+marked with [[no_unique_address]].
+"""
+
+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+class NoUniqueAddressTestCase(TestBase):
+ def test(self):
+ self.build()
+ lldbutil.run_to_source_breakpoint(
+ self, "return 0", lldb.SBFileSpec("main.cpp", False)
+ )
+
+ # Qualified/unqualified lookup to templates in namespace
+ self.expect_expr("b1", result_type="basic::Foo", result_children=[ValueCheck(
+ name="a", type="Empty"
+ )])
+
+ self.expect_expr("b2", result_type="bases::Foo", result_children=[
+ ValueCheck(type="bases::B", children=[
+ ValueCheck(name="x", type="Empty")
+ ]),
+ ValueCheck(type="bases::A", children=[
+ ValueCheck(name="c", type="long", value="1"),
+ ValueCheck(name="d", type="long", value="2")
+ ]),
+ ValueCheck(type="bases::C", children=[
+ ValueCheck(name="x", type="Empty")
+ ]),
+ ])
+ self.expect_expr("b3", result_type="bases::Bar", result_children=[
+ ValueCheck(type="bases::B", children=[
+ ValueCheck(name="x", type="Empty")
+ ]),
+ ValueCheck(type="bases::C", children=[
+ ValueCheck(name="x", type="Empty")
+ ]),
+ ValueCheck(type="bases::A", children=[
+ ValueCheck(name="c", type="long", value="5"),
+ ValueCheck(name="d", type="long", value="6")
+ ]),
+ ])
+
+ self.expect("frame var b1")
+ self.expect("frame var b2")
+ self.expect("frame var b3")
diff --git a/lldb/test/API/lang/cpp/no_unique_address/main.cpp b/lldb/test/API/lang/cpp/no_unique_address/main.cpp
new file mode 100644
index 0000000000000..424fa90859cea
--- /dev/null
+++ b/lldb/test/API/lang/cpp/no_unique_address/main.cpp
@@ -0,0 +1,35 @@
+struct Empty {};
+
+namespace basic {
+struct Foo {
+ [[no_unique_address]] Empty a;
+};
+} // namespace basic
+
+namespace bases {
+struct A {
+ long c, d;
+};
+
+struct B {
+ [[no_unique_address]] Empty x;
+};
+
+struct C {
+ [[no_unique_address]] Empty x;
+};
+
+struct Foo : B, A, C {};
+struct Bar : B, C, A {};
+} // namespace bases
+
+int main() {
+ basic::Foo b1;
+ bases::Foo b2;
+ bases::Bar b3;
+ b2.c = 1;
+ b2.d = 2;
+ b3.c = 5;
+ b3.d = 6;
+ return 0;
+}
``````````
</details>
https://github.com/llvm/llvm-project/pull/93809
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