[C++20] [Modules] [Reduced BMI] Handling Deduction Guide in reduced BMI

carefully

Close #93859

The direct pattern of the issue is that, in a reduced BMI, we're going
to wrtie a class but we didn't write the deduction guide. Although we
handled deduction guide, but we tried to record the found deduction
guide from `noload_lookup` directly.

It is slightly problematic if the found deduction guide is from AST.
e.g.,

```
module;
export module m;
import xxx; // Also contains the class and the deduction guide
...
```

Then when we writes the class in the current file, we tried to record
the deduction guide, but `noload_lookup` returns the deduction guide
from the AST file then we didn't record the local deduction guide. Then
mismatch happens.

To mitiagte the problem, we tried to record the canonical declaration
for the decution guide.

Author: ChuanqiXu9

clang/lib/Serialization/ASTWriterDecl.cpp

@@ -1733,7 +1733,7 @@ void ASTDeclWriter::VisitClassTemplateDecl(ClassTemplateDecl *D) {
   if (Writer.isGeneratingReducedBMI()) {
     auto Name = Context.DeclarationNames.getCXXDeductionGuideName(D);
     for (auto *DG : D->getDeclContext()->noload_lookup(Name))
-      Writer.GetDeclRef(DG);
+      Writer.GetDeclRef(DG->getCanonicalDecl());
   }
 
   Code = serialization::DECL_CLASS_TEMPLATE;

clang/test/Modules/pr93859.cppm

@@ -0,0 +1,146 @@
+// Reduced from https://github.com/llvm/llvm-project/issues/93859
+//
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: split-file %s %t
+//
+// RUN: %clang_cc1 -std=c++20 %t/reduced_std.cppm -emit-reduced-module-interface -o %t/reduced_std.pcm
+// RUN: %clang_cc1 -std=c++20 %t/Misc.cppm -emit-reduced-module-interface -o %t/Misc.pcm \
+// RUN:     -fprebuilt-module-path=%t
+// RUN: %clang_cc1 -std=c++20 %t/Instance.cppm -emit-reduced-module-interface -o %t/Instance.pcm \
+// RUN:     -fprebuilt-module-path=%t
+// RUN: %clang_cc1 -std=c++20 %t/Device.cppm -emit-reduced-module-interface -o %t/Device.pcm \
+// RUN:     -fprebuilt-module-path=%t
+// RUN: %clang_cc1 -std=c++20 %t/Overlay.cppm -emit-reduced-module-interface -o %t/Overlay.pcm \
+// RUN:     -fprebuilt-module-path=%t
+// RUN: %clang_cc1 -std=c++20 %t/App.cppm -emit-module-interface -o /dev/null \
+// RUN:     -fexperimental-modules-reduced-bmi -fmodule-output=%t/App.pcm \
+// RUN:     -fprebuilt-module-path=%t
+// RUN: %clang_cc1 -std=c++20 %t/test.cc -fsyntax-only -verify \
+// RUN:     -fprebuilt-module-path=%t
+
+//--- header.h
+namespace std {
+
+template <class _T1, class _T2>
+struct pair
+{
+  _T1 first;
+  _T2 second;
+
+  constexpr pair()
+      : first(), second() {}
+
+  constexpr pair(_T1 const& __t1, _T2 const& __t2)
+      : first(__t1), second(__t2) {}
+};
+
+template <class _T1, class _T2>
+pair(_T1, _T2) -> pair<_T1, _T2>;
+
+template <class _Tp>
+class __tree_const_iterator {
+public:
+  template <class>
+  friend class __tree;
+};
+
+template <class _Tp>
+class __tree {
+public:
+  typedef _Tp value_type;
+  typedef __tree_const_iterator<value_type> const_iterator;
+
+  template <class, class, class, class>
+  friend class map;
+};
+
+template <class _Key>
+class set {
+public:
+  typedef __tree<_Key> __base;
+
+  typedef typename __base::const_iterator iterator;
+
+  set() {}
+
+  pair<iterator, bool>
+  insert(const _Key& __v);
+};
+
+template <class _InputIterator, class _OutputIterator>
+inline constexpr _OutputIterator
+copy(_InputIterator __first, _InputIterator __last, _OutputIterator __result) {
+  return pair{__first, __last}.second;
+}
+
+}
+
+//--- reduced_std.cppm
+module;
+#include "header.h"
+export module reduced_std;
+
+export namespace std {
+    using std::set;
+    using std::copy;
+}
+
+//--- Misc.cppm
+export module Misc;
+import reduced_std;
+
+export void check_result(int res) {
+    std::set<char> extensions;
+    extensions.insert('f');
+}
+
+//--- Instance.cppm
+export module Instance;
+import reduced_std;
+
+export class Instance {
+public:
+    Instance() {
+        std::set<const char*> extensions;
+        extensions.insert("foo");
+    }
+};
+
+//--- Device.cppm
+export module Device;
+import reduced_std;
+import Instance;
+import Misc;
+
+std::set<int> wtf_set;
+
+//--- Overlay.cppm
+export module Overlay;
+
+import reduced_std;
+import Device;
+
+void overlay_vector_use() {
+    std::set<int> nums;
+    nums.insert(1);
+}
+
+//--- App.cppm
+module;
+#include "header.h"
+export module App;
+import Overlay;
+
+std::set<float> fs;
+
+//--- test.cc
+// expected-no-diagnostics
+import reduced_std;
+import App;
+
+void render() {
+    unsigned *oidxs = nullptr;
+    unsigned idxs[] = {0, 1, 2, 0, 2, 3};
+    std::copy(idxs, idxs + 6, oidxs);
+}