[Coroutines] Remove unused coroutine builtin/intrinsics llvm.coro.param (NFC-ish)

I found that the coroutine intrinsic llvm.coro.param in documentation
(https://llvm.org/docs/Coroutines.html#id101) didn't get used actually
since there isn't lowering codes in LLVM. I also checked the
implementation of libstdc++ and libc++. Both of them didn't use
llvm.coro.param. So I am pretty sure that the llvm.coro.param intrinsic
is unused. I think it would be better t to remove it to avoid possible
misleading understandings.

Note: according to [class.copy.elision]/p1.3, this optimization is
allowed by the C++ language specification. Let's make it someday.

Reviewed By: rjmccall

Differential Revision: https://reviews.llvm.org/D115222

clang/docs/LanguageExtensions.rst

@@ -3007,7 +3007,6 @@ an appropriate value during the emission.
   void  *__builtin_coro_begin(void *memory)
   void   __builtin_coro_end(void *coro_frame, bool unwind)
   char   __builtin_coro_suspend(bool final)
-  bool   __builtin_coro_param(void *original, void *copy)
 
 Note that there is no builtin matching the `llvm.coro.save` intrinsic. LLVM
 automatically will insert one if the first argument to `llvm.coro.suspend` is

clang/include/clang/Basic/Builtins.def

@@ -1612,7 +1612,6 @@ LANGBUILTIN(__builtin_coro_alloc, "b", "n", COR_LANG)
 LANGBUILTIN(__builtin_coro_begin, "v*v*", "n", COR_LANG)
 LANGBUILTIN(__builtin_coro_end, "bv*Ib", "n", COR_LANG)
 LANGBUILTIN(__builtin_coro_suspend, "cIb", "n", COR_LANG)
-LANGBUILTIN(__builtin_coro_param, "bv*v*", "n", COR_LANG)
 
 // OpenCL v2.0 s6.13.16, s9.17.3.5 - Pipe functions.
 // We need the generic prototype, since the packet type could be anything.

clang/lib/CodeGen/CGBuiltin.cpp

@@ -4702,8 +4702,6 @@ RValue CodeGenFunction::EmitBuiltinExpr(const GlobalDecl GD, unsigned BuiltinID,
     return EmitCoroutineIntrinsic(E, Intrinsic::coro_end);
   case Builtin::BI__builtin_coro_suspend:
     return EmitCoroutineIntrinsic(E, Intrinsic::coro_suspend);
-  case Builtin::BI__builtin_coro_param:
-    return EmitCoroutineIntrinsic(E, Intrinsic::coro_param);
 
   // OpenCL v2.0 s6.13.16.2, Built-in pipe read and write functions
   case Builtin::BIread_pipe:

clang/test/CodeGenCoroutines/coro-builtins.c

@@ -5,9 +5,7 @@ void *myAlloc(long long);
 // CHECK-LABEL: f(
 void f(int n) {
   // CHECK: %n.addr = alloca i32
-  // CHECK: %n_copy = alloca i32
   // CHECK: %promise = alloca i32
-  int n_copy;
   int promise;
 
   // CHECK: %[[PROM_ADDR:.+]] = bitcast i32* %promise to i8*
@@ -45,9 +43,4 @@ void f(int n) {
 
   // CHECK-NEXT: call i8 @llvm.coro.suspend(token none, i1 true)
   __builtin_coro_suspend(1);
-
-  // CHECK-NEXT: %[[N_ADDR:.+]] = bitcast i32* %n.addr to i8*
-  // CHECK-NEXT: %[[N_COPY_ADDR:.+]] = bitcast i32* %n_copy to i8*
-  // CHECK-NEXT: call i1 @llvm.coro.param(i8* %[[N_ADDR]], i8* %[[N_COPY_ADDR]])
-  __builtin_coro_param(&n, &n_copy);
 }

llvm/docs/Coroutines.rst

@@ -1644,89 +1644,6 @@ a call to ``llvm.coro.suspend.retcon`` after resuming abnormally.
 In a yield-once coroutine, it is undefined behavior if the coroutine
 executes a call to ``llvm.coro.suspend.retcon`` after resuming in any way.
 
-.. _coro.param:
-
-'llvm.coro.param' Intrinsic
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-::
-
-  declare i1 @llvm.coro.param(i8* <original>, i8* <copy>)
-
-Overview:
-"""""""""
-
-The '``llvm.coro.param``' is used by a frontend to mark up the code used to
-construct and destruct copies of the parameters. If the optimizer discovers that
-a particular parameter copy is not used after any suspends, it can remove the
-construction and destruction of the copy by replacing corresponding coro.param
-with `i1 false` and replacing any use of the `copy` with the `original`.
-
-Arguments:
-""""""""""
-
-The first argument points to an `alloca` storing the value of a parameter to a
-coroutine.
-
-The second argument points to an `alloca` storing the value of the copy of that
-parameter.
-
-Semantics:
-""""""""""
-
-The optimizer is free to always replace this intrinsic with `i1 true`.
-
-The optimizer is also allowed to replace it with `i1 false` provided that the
-parameter copy is only used prior to control flow reaching any of the suspend
-points. The code that would be DCE'd if the `coro.param` is replaced with
-`i1 false` is not considered to be a use of the parameter copy.
-
-The frontend can emit this intrinsic if its language rules allow for this
-optimization.
-
-Example:
-""""""""
-Consider the following example. A coroutine takes two parameters `a` and `b`
-that has a destructor and a move constructor.
-
-.. code-block:: c++
-
-  struct A { ~A(); A(A&&); bool foo(); void bar(); };
-
-  task<int> f(A a, A b) {
-    if (a.foo())
-      return 42;
-
-    a.bar();
-    co_await read_async(); // introduces suspend point
-    b.bar();
-  }
-
-Note that, uses of `b` is used after a suspend point and thus must be copied
-into a coroutine frame, whereas `a` does not have to, since it never used
-after suspend.
-
-A frontend can create parameter copies for `a` and `b` as follows:
-
-.. code-block:: text
-
-  task<int> f(A a', A b') {
-    a = alloca A;
-    b = alloca A;
-    // move parameters to its copies
-    if (coro.param(a', a)) A::A(a, A&& a');
-    if (coro.param(b', b)) A::A(b, A&& b');
-    ...
-    // destroy parameters copies
-    if (coro.param(a', a)) A::~A(a);
-    if (coro.param(b', b)) A::~A(b);
-  }
-
-The optimizer can replace coro.param(a',a) with `i1 false` and replace all uses
-of `a` with `a'`, since it is not used after suspend.
-
-The optimizer must replace coro.param(b', b) with `i1 true`, since `b` is used
-after suspend and therefore, it has to reside in the coroutine frame.
-
 Coroutine Transformation Passes
 ===============================
 CoroEarly

llvm/include/llvm/Analysis/TargetTransformInfoImpl.h

@@ -625,7 +625,6 @@ public:
     case Intrinsic::coro_frame:
     case Intrinsic::coro_size:
     case Intrinsic::coro_suspend:
-    case Intrinsic::coro_param:
     case Intrinsic::coro_subfn_addr:
       // These intrinsics don't actually represent code after lowering.
       return 0;

llvm/include/llvm/IR/Intrinsics.td

@@ -1282,10 +1282,6 @@ def int_coro_alloca_alloc : Intrinsic<[llvm_token_ty],
 def int_coro_alloca_get : Intrinsic<[llvm_ptr_ty], [llvm_token_ty], []>;
 def int_coro_alloca_free : Intrinsic<[], [llvm_token_ty], []>;
 
-def int_coro_param : Intrinsic<[llvm_i1_ty], [llvm_ptr_ty, llvm_ptr_ty],
-                               [IntrNoMem, ReadNone<ArgIndex<0>>,
-                                ReadNone<ArgIndex<1>>]>;
-
 // Coroutine Manipulation Intrinsics.
 
 def int_coro_resume : Intrinsic<[], [llvm_ptr_ty], [Throws]>;

llvm/lib/Transforms/Coroutines/Coroutines.cpp

@@ -141,7 +141,6 @@ static bool isCoroutineIntrinsicName(StringRef Name) {
       "llvm.coro.id.retcon",
       "llvm.coro.id.retcon.once",
       "llvm.coro.noop",
-      "llvm.coro.param",
       "llvm.coro.prepare.async",
       "llvm.coro.prepare.retcon",
       "llvm.coro.promise",