[all-commits] [llvm/llvm-project] 030047: [Clang] Eagerly instantiate used constexpr functio...

[cor3ntin via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 030047c432cac133738be68fa0974f70e69dd58d
      https://github.com/llvm/llvm-project/commit/030047c432cac133738be68fa0974f70e69dd58d
  Author: cor3ntin <corentinjabot at gmail.com>
  Date:   2023-11-30 (Thu, 30 Nov 2023)

  Changed paths:
    M clang/docs/ReleaseNotes.rst
    M clang/include/clang/Sema/ExternalSemaSource.h
    M clang/include/clang/Sema/MultiplexExternalSemaSource.h
    M clang/include/clang/Sema/Sema.h
    M clang/include/clang/Serialization/ASTBitCodes.h
    M clang/include/clang/Serialization/ASTReader.h
    M clang/lib/Sema/MultiplexExternalSemaSource.cpp
    M clang/lib/Sema/SemaDecl.cpp
    M clang/lib/Sema/SemaExpr.cpp
    M clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
    M clang/lib/Serialization/ASTReader.cpp
    M clang/lib/Serialization/ASTWriter.cpp
    A clang/test/PCH/instantiate-used-constexpr-function.cpp
    A clang/test/SemaTemplate/instantiate-used-constexpr-function.cpp

  Log Message:
  -----------
  [Clang] Eagerly instantiate used constexpr function upon definition. (#73463)

Despite CWG2497 not being resolved, it is reasonable to expect the
following code to compile (and which is supported by other compilers)

```cpp
  template<typename T> constexpr T f();
  constexpr int g() { return f<int>(); } // #1
  template<typename T> constexpr T f() { return 123; }
  int k[g()];
  // #2
```

To that end, we eagerly instantiate all referenced specializations of
constexpr functions when they are defined.

We maintain a map of (pattern, [instantiations]) independent of
`PendingInstantiations` to avoid having to iterate that list after each
function definition.

We should apply the same logic to constexpr variables, but I wanted to
keep the PR small.

Fixes #73232