[clang] a4f75ec - [C++20] [Modules] Don't record implicitly declarations to BMI by default (#93459)

[via cfe-commits]

Author: Chuanqi Xu
Date: 2024-05-28T09:36:30+08:00
New Revision: a4f75ec730ee573fc35a51264a907b1f05b53e3b

URL: https://github.com/llvm/llvm-project/commit/a4f75ec730ee573fc35a51264a907b1f05b53e3b
DIFF: https://github.com/llvm/llvm-project/commit/a4f75ec730ee573fc35a51264a907b1f05b53e3b.diff

LOG: [C++20] [Modules] Don't record implicitly declarations to BMI by default (#93459)

I found we may insert unused implciit declarations like AArch SVE
declarations by default on AArch64 due to we will insert that by
default. But it should be completely redundant and this patch tries to
remove that.

Added: 
    clang/test/Modules/no-implicit-declarations.cppm

Modified: 
    clang/lib/Serialization/ASTWriter.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index 00b0e48083217..a85cd94fd5b5a 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -5037,6 +5037,14 @@ void ASTWriter::PrepareWritingSpecialDecls(Sema &SemaRef) {
         continue;
     }
 
+    // If we're writing C++ named modules, don't emit declarations which are
+    // not from modules by default. They may be built in declarations (be
+    // handled above) or implcit declarations (see the implementation of
+    // `Sema::Initialize()` for example).
+    if (isWritingStdCXXNamedModules() && !D->getOwningModule() &&
+        D->isImplicit())
+      continue;
+
     GetDeclRef(D);
   }
 
@@ -6197,8 +6205,9 @@ bool ASTWriter::wasDeclEmitted(const Decl *D) const {
     return true;
 
   bool Emitted = DeclIDs.contains(D);
-  assert((Emitted || GeneratingReducedBMI) &&
-         "The declaration can only be omitted in reduced BMI.");
+  assert((Emitted || (!D->getOwningModule() && isWritingStdCXXNamedModules()) ||
+          GeneratingReducedBMI) &&
+         "The declaration within modules can only be omitted in reduced BMI.");
   return Emitted;
 }
 

diff  --git a/clang/test/Modules/no-implicit-declarations.cppm b/clang/test/Modules/no-implicit-declarations.cppm
new file mode 100644
index 0000000000000..319d3a432ea23
--- /dev/null
+++ b/clang/test/Modules/no-implicit-declarations.cppm
@@ -0,0 +1,26 @@
+// RUN: rm -rf %t
+// RUN: mkdir %t
+//
+// RUN: %clang_cc1 -std=c++20 %s -emit-module-interface -o %t/a.pcm
+// RUN: llvm-bcanalyzer --dump --disable-histogram --show-binary-blobs %t/a.pcm > %t/a.dump
+// RUN: cat %t/a.dump | FileCheck %s
+//
+// RUN: %clang_cc1 -std=c++20 %s -emit-reduced-module-interface -o %t/a.pcm
+// RUN: llvm-bcanalyzer --dump --disable-histogram --show-binary-blobs %t/a.pcm > %t/a.dump
+// RUN: cat %t/a.dump | FileCheck %s
+
+export module a;
+// Contain something at least to make sure the compiler won't
+// optimize this out.
+export int a = 43;
+
+// CHECK:  <DECLTYPES_BLOCK
+// CHECK-NOT: <DECL_TYPEDEF
+// CHECK:    <DECL_CONTEXT_LEXICAL
+// CHECK:    <UnknownCode
+// CHECK:    <TYPE_TYPEDEF
+// CHECK:    <DECL_VAR
+// CHECK:    <EXPR_INTEGER_LITERAL
+// CHECK:    <STMT_STOP
+// CHECK:    <TYPE_RECORD
+// CHECK:  </DECLTYPES_BLOCK>