[Clang][NFC] Remove CallExpr::CreateTemporary (#130919)

`CallExpr::CreateTemporary` was only used to deduce a conversion
sequence from a conversion operator.

We only need a type/value category for that,
so we can use a dummy Expression such as a
`OpaqueValueExpr`.

This simplify the code and avoid partially-formed
`CallExpr` with incorrect invariants (see #130725)

Fixes #130824

Author: cor3ntin

clang/include/clang/AST/Expr.h

@@ -3005,18 +3005,6 @@ class CallExpr : public Expr {
                           FPOptionsOverride FPFeatures, unsigned MinNumArgs = 0,
                           ADLCallKind UsesADL = NotADL);
 
-  /// Create a temporary call expression with no arguments in the memory
-  /// pointed to by Mem. Mem must points to at least sizeof(CallExpr)
-  /// + sizeof(Stmt *) bytes of storage, aligned to alignof(CallExpr):
-  ///
-  /// \code{.cpp}
-  ///   alignas(CallExpr) char Buffer[sizeof(CallExpr) + sizeof(Stmt *)];
-  ///   CallExpr *TheCall = CallExpr::CreateTemporary(Buffer, etc);
-  /// \endcode
-  static CallExpr *CreateTemporary(void *Mem, Expr *Fn, QualType Ty,
-                                   ExprValueKind VK, SourceLocation RParenLoc,
-                                   ADLCallKind UsesADL = NotADL);
-
   /// Create an empty call expression, for deserialization.
   static CallExpr *CreateEmpty(const ASTContext &Ctx, unsigned NumArgs,
                                bool HasFPFeatures, EmptyShell Empty);

clang/lib/AST/Expr.cpp

@@ -1509,16 +1509,6 @@ CallExpr *CallExpr::Create(const ASTContext &Ctx, Expr *Fn,
                             RParenLoc, FPFeatures, MinNumArgs, UsesADL);
 }
 
-CallExpr *CallExpr::CreateTemporary(void *Mem, Expr *Fn, QualType Ty,
-                                    ExprValueKind VK, SourceLocation RParenLoc,
-                                    ADLCallKind UsesADL) {
-  assert(!(reinterpret_cast<uintptr_t>(Mem) % alignof(CallExpr)) &&
-         "Misaligned memory in CallExpr::CreateTemporary!");
-  return new (Mem) CallExpr(CallExprClass, Fn, /*PreArgs=*/{}, /*Args=*/{}, Ty,
-                            VK, RParenLoc, FPOptionsOverride(),
-                            /*MinNumArgs=*/0, UsesADL);
-}
-
 CallExpr *CallExpr::CreateEmpty(const ASTContext &Ctx, unsigned NumArgs,
                                 bool HasFPFeatures, EmptyShell Empty) {
   unsigned SizeOfTrailingObjects =
@@ -1655,14 +1645,8 @@ SourceLocation CallExpr::getBeginLoc() const {
   if (!isTypeDependent()) {
     if (const auto *Method =
             dyn_cast_if_present<const CXXMethodDecl>(getCalleeDecl());
-        Method && Method->isExplicitObjectMemberFunction()) {
-      // Note: while we typically expect the call to have a first argument
-      // here, we can't assert it because in some cases it does not, e.g.
-      // calls created with CallExpr::CreateTemporary() during overload
-      // resolution.
-      if (getNumArgs() > 0 && getArg(0))
-        return getArg(0)->getBeginLoc();
-    }
+        Method && Method->isExplicitObjectMemberFunction())
+      return getArg(0)->getBeginLoc();
   }
 
   SourceLocation begin = getCallee()->getBeginLoc();

clang/lib/Sema/SemaOverload.cpp

@@ -8147,17 +8147,14 @@ void Sema::AddConversionCandidate(
 
   ExprValueKind VK = Expr::getValueKindForType(ConversionType);
 
-  // Note that it is safe to allocate CallExpr on the stack here because
-  // there are 0 arguments (i.e., nothing is allocated using ASTContext's
-  // allocator).
   QualType CallResultType = ConversionType.getNonLValueExprType(Context);
 
-  alignas(CallExpr) char Buffer[sizeof(CallExpr) + sizeof(Stmt *)];
-  CallExpr *TheTemporaryCall = CallExpr::CreateTemporary(
-      Buffer, &ConversionFn, CallResultType, VK, From->getBeginLoc());
+  // Introduce a temporary expression with the right type and value category
+  // that we can use for deduction purposes.
+  OpaqueValueExpr FakeCall(From->getBeginLoc(), CallResultType, VK);
 
   ImplicitConversionSequence ICS =
-      TryCopyInitialization(*this, TheTemporaryCall, ToType,
+      TryCopyInitialization(*this, &FakeCall, ToType,
                             /*SuppressUserConversions=*/true,
                             /*InOverloadResolution=*/false,
                             /*AllowObjCWritebackConversion=*/false);