[clang] static operators should evaluate object argument (#68485)

### Description

clang don't evaluate the object argument of `static operator()` and
`static operator[]` currently, for example:

```cpp
#include <iostream>

struct Foo {
    static int operator()(int x, int y) {
        std::cout << "Foo::operator()" << std::endl;
        return x + y;
    }
    static int operator[](int x, int y) {
        std::cout << "Foo::operator[]" << std::endl;
        return x + y;
    }
};
Foo getFoo() {
    std::cout << "getFoo()" << std::endl;
    return {};
}
int main() {
    std::cout << getFoo()(1, 2) << std::endl;
    std::cout << getFoo()[1, 2] << std::endl;
}
```

`getFoo()` is expected to be called, but clang don't call it currently
(17.0.2). This PR fixes this issue.

Fixes #67976.

### Walkthrough

- **clang/lib/Sema/SemaOverload.cpp**
- **`Sema::CreateOverloadedArraySubscriptExpr` &
`Sema::BuildCallToObjectOfClassType`**
Previously clang generate `CallExpr` for static operators, ignoring the
object argument. In this PR `CXXOperatorCallExpr` is generated for
static operators instead, with the object argument as the first
argument.
  - **`TryObjectArgumentInitialization`**
`const` / `volatile` objects are allowed for static methods, so that we
can call static operators on them.
- **clang/lib/CodeGen/CGExpr.cpp**
  - **`CodeGenFunction::EmitCall`**
CodeGen changes for `CXXOperatorCallExpr` with static operators: emit
and ignore the object argument first, then emit the operator call.
- **clang/lib/AST/ExprConstant.cpp**
  - **`‎ExprEvaluatorBase::handleCallExpr‎`**
Evaluation of static operators in constexpr also need some small changes
to work, so that the arguments won't be out of position.
- **clang/lib/Sema/SemaChecking.cpp**
  - **`Sema::CheckFunctionCall`**
Code for argument checking also need to be modify, or it will fail the
test `clang/test/SemaCXX/overloaded-operator-decl.cpp`.

### Tests

- **Added:**
    - **clang/test/AST/ast-dump-static-operators.cpp**
      Verify the AST generated for static operators.
    - **clang/test/SemaCXX/cxx2b-static-operator.cpp**
Static operators should be able to be called on const / volatile
objects.
- **Modified:**
    - **clang/test/CodeGenCXX/cxx2b-static-call-operator.cpp**
    - **clang/test/CodeGenCXX/cxx2b-static-subscript-operator.cpp**
      Matching the new CodeGen.

### Documentation

- **clang/docs/ReleaseNotes.rst**
  Update release notes.

---------

Co-authored-by: Shafik Yaghmour <shafik@users.noreply.github.com>
Co-authored-by: cor3ntin <corentinjabot@gmail.com>
Co-authored-by: Aaron Ballman <aaron@aaronballman.com>

1 files changed, 15 insertions, 2 deletions

diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index 8c8c937b512a..4a2f3caad658 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -5848,6 +5848,7 @@ RValue CodeGenFunction::EmitCall(QualType CalleeType, const CGCallee &OrigCallee
   // destruction order is not necessarily reverse construction order.
   // FIXME: Revisit this based on C++ committee response to unimplementability.
   EvaluationOrder Order = EvaluationOrder::Default;
+  bool StaticOperator = false;
   if (auto *OCE = dyn_cast<CXXOperatorCallExpr>(E)) {
     if (OCE->isAssignmentOp())
       Order = EvaluationOrder::ForceRightToLeft;
@@ -5865,10 +5866,22 @@ RValue CodeGenFunction::EmitCall(QualType CalleeType, const CGCallee &OrigCallee
         break;
       }
     }
+
+    if (const auto *MD =
+            dyn_cast_if_present<CXXMethodDecl>(OCE->getCalleeDecl());
+        MD && MD->isStatic())
+      StaticOperator = true;
   }
 
-  EmitCallArgs(Args, dyn_cast<FunctionProtoType>(FnType), E->arguments(),
-               E->getDirectCallee(), /*ParamsToSkip*/ 0, Order);
+  auto Arguments = E->arguments();
+  if (StaticOperator) {
+    // If we're calling a static operator, we need to emit the object argument
+    // and ignore it.
+    EmitIgnoredExpr(E->getArg(0));
+    Arguments = drop_begin(Arguments, 1);
+  }
+  EmitCallArgs(Args, dyn_cast<FunctionProtoType>(FnType), Arguments,
+               E->getDirectCallee(), /*ParamsToSkip=*/0, Order);
 
   const CGFunctionInfo &FnInfo = CGM.getTypes().arrangeFreeFunctionCall(
       Args, FnType, /*ChainCall=*/Chain);