[clang] 534e2dd - [Clang][Interp] Visit `DecompositionDecl` and create a local variable (#100400)

[via cfe-commits]

Author: yronglin
Date: 2024-07-25T19:44:25+08:00
New Revision: 534e2dd29f252cc13b94312895d2f4b39b54b9d4

URL: https://github.com/llvm/llvm-project/commit/534e2dd29f252cc13b94312895d2f4b39b54b9d4
DIFF: https://github.com/llvm/llvm-project/commit/534e2dd29f252cc13b94312895d2f4b39b54b9d4.diff

LOG: [Clang][Interp] Visit `DecompositionDecl` and create a local variable (#100400)

The following code should be well-formed:
```C++
float decompose_complex(_Complex float cf) {
  static _Complex float scf;
  auto &[sre, sim] = scf;
  // ok, this is references initialized by constant expressions all the way down
  static_assert(&sre == &__real scf);
  static_assert(&sim == &__imag scf);

  auto [re, im] = cf;
  return re*re + im*im;
}

```
We should visit `DecompositionDecl` and create a local variable but not
a create a dummy value directly.

---------

Signed-off-by: yronglin <yronglin777 at gmail.com>

Added: 
    

Modified: 
    clang/lib/AST/Interp/Compiler.cpp
    clang/test/SemaCXX/cxx1z-decomposition.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/AST/Interp/Compiler.cpp b/clang/lib/AST/Interp/Compiler.cpp
index df55d01b8b9d6..11ca7f210d2d5 100644
--- a/clang/lib/AST/Interp/Compiler.cpp
+++ b/clang/lib/AST/Interp/Compiler.cpp
@@ -5239,6 +5239,10 @@ bool Compiler<Emitter>::visitDeclRef(const ValueDecl *D, const Expr *E) {
           return false;
         };
 
+        // DecompositionDecls are just proxies for us.
+        if (isa<DecompositionDecl>(VD))
+          return revisit(VD);
+
         // Visit local const variables like normal.
         if ((VD->hasGlobalStorage() || VD->isLocalVarDecl() ||
              VD->isStaticDataMember()) &&

diff  --git a/clang/test/SemaCXX/cxx1z-decomposition.cpp b/clang/test/SemaCXX/cxx1z-decomposition.cpp
index 305a9ac2ebc24..19c730303625e 100644
--- a/clang/test/SemaCXX/cxx1z-decomposition.cpp
+++ b/clang/test/SemaCXX/cxx1z-decomposition.cpp
@@ -1,5 +1,6 @@
 // RUN: %clang_cc1 -std=c++17 -Wc++20-extensions -verify=expected %s
 // RUN: %clang_cc1 -std=c++20 -Wpre-c++20-compat -verify=expected %s
+// RUN: %clang_cc1 -std=c++20 -Wpre-c++20-compat -fexperimental-new-constant-interpreter -verify=expected %s
 
 void use_from_own_init() {
   auto [a] = a; // expected-error {{binding 'a' cannot appear in the initializer of its own decomposition declaration}}