[Coroutines] [Frontend] Lookup in std namespace first

Now in libcxx and clang, all the coroutine components are defined in
std::experimental namespace.
And now the coroutine TS is merged into C++20.

[Coroutines] [Frontend] Lookup in std namespace first

Now in libcxx and clang, all the coroutine components are defined in
std::experimental namespace.
And now the coroutine TS is merged into C++20. So in the working draft
like N4892, we could find the coroutine components is defined in std
namespace instead of std::experimental namespace.
And the coroutine support in clang seems to be relatively stable. So I
think it may be suitable to move the coroutine component into the
experiment namespace now.

This patch would make clang lookup coroutine_traits in std namespace
first. For the compatibility consideration, clang would lookup in
std::experimental namespace if it can't find definitions in std
namespace. So the existing codes wouldn't be break after update
compiler.

And in case the compiler found std::coroutine_traits and
std::experimental::coroutine_traits at the same time, it would emit an
error for it.

The support for looking up std::experimental::coroutine_traits would be
removed in Clang16.

Reviewed By: lxfind, Quuxplusone

Differential Revision: https://reviews.llvm.org/D108696

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Revert "[Coroutines] [Clang] Look up coroutine component in std namespace first"

This reverts commit 2fbd254aa46b, which broke the libc++ CI. I'm reverting
to get things stable again until we've fig

Revert "[Coroutines] [Clang] Look up coroutine component in std namespace first"

This reverts commit 2fbd254aa46b, which broke the libc++ CI. I'm reverting
to get things stable again until we've figured out a way forward.

Differential Revision: https://reviews.llvm.org/D108696

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[Coroutines] [Clang] Look up coroutine component in std namespace first

Summary: Now in libcxx and clang, all the coroutine components are
defined in std::experimental namespace.
And now the corouti

[Coroutines] [Clang] Look up coroutine component in std namespace first

Summary: Now in libcxx and clang, all the coroutine components are
defined in std::experimental namespace.
And now the coroutine TS is merged into C++20. So in the working draft
like N4892, we could find the coroutine components is defined in std
namespace instead of std::experimental namespace.
And the coroutine support in clang seems to be relatively stable. So I
think it may be suitable to move the coroutine component into the
experiment namespace now.

But move the coroutine component into the std namespace may be an break
change. So I planned to split this change into two patch. One in clang
and other in libcxx.

This patch would make clang lookup coroutine_traits in std namespace
first. For the compatibility consideration, clang would lookup in
std::experimental namespace if it can't find definitions in std
namespace and emit a warning in this case. So the existing codes
wouldn't be break after update compiler.

Test Plan: check-clang, check-libcxx

Reviewed By: lxfind

Differential Revision: https://reviews.llvm.org/D108696

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[DIBuilder] Do not replace empty enum types

It looks like this array was missed in 4276d4a8d08b7640eb57cabf6988a5cf65b228b6

Fixed tests that expected `elements` to be empty or depeneded on the orde

[DIBuilder] Do not replace empty enum types

It looks like this array was missed in 4276d4a8d08b7640eb57cabf6988a5cf65b228b6

Fixed tests that expected `elements` to be empty or depeneded on the order of the empty DINode.

Reviewed By: aprantl

Differential Revision: https://reviews.llvm.org/D107024

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[Clang][Coroutine][DebugInfo] Relax test ordering requirement

The test added in D97533 (and modified by this patch) has some overly
strict printed metadata ordering requirements, specifically the
in

[Clang][Coroutine][DebugInfo] Relax test ordering requirement

The test added in D97533 (and modified by this patch) has some overly
strict printed metadata ordering requirements, specifically the
interleaving of DILocalVariable nodes and DILocation nodes. Slight changes
in metadata emission can easily break this unfortunately.

This patch stops after clang codegen rather than allowing the coro splitter
to run, and reduces the need for ordering: it picks out the
DILocalVariable nodes being sought, in any order (CHECK-DAG), and doesn't
examine any DILocations. The implicit CHECK-NOT is what's important: the
test seeks to ensure a duplicate set of DILocalVariables aren't emitted in
the same scope.

Differential Revision: https://reviews.llvm.org/D100298

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[Clang][Coroutine][DebugInfo] In c++ coroutine, clang will emit different debug info variables for parameters and move-parameters.

The first one is the real parameters of the coroutine function, the

[Clang][Coroutine][DebugInfo] In c++ coroutine, clang will emit different debug info variables for parameters and move-parameters.

The first one is the real parameters of the coroutine function, the
other one just for copying parameters to the coroutine frame.

Considering the following c++ code:
```
struct coro {
...
};

coro foo(struct test & t) {
...
co_await suspend_always();
...
co_await suspend_always();
...
co_await suspend_always();
}

int main(int argc, char *argv[]) {
auto c = foo(...);
c.handle.resume();
...
}
```

Function foo is the standard coroutine function, and it has only
one parameter named t (ignoring this at first),
when we use the llvm code to compile this function, we can get the
following ir:

```
!2921 = distinct !DISubprogram(name: "foo", linkageName:
"_ZN6Object3fooE4test", scope: !2211, file: !45, li\
ne: 48, type: !2329, scopeLine: 48, flags: DIFlagPrototyped |
DIFlagAllCallsDescribed, spFlags: DISPFlagDefi\
nition | DISPFlagOptimized, unit: !44, declaration: !2328,
retainedNodes: !2922)
!2924 = !DILocalVariable(name: "t", arg: 2, scope: !2921, file: !45,
line: 48, type: !838)
...
!2926 = !DILocalVariable(name: "t", scope: !2921, type: !838, flags:
DIFlagArtificial)
```
We can find there are two `the same` DIVariable named t in the same
dwarf scope for foo.resume.
And when we try to use llvm-dwarfdump to dump the dwarf info of this
elf, we get the following output:

```
0x00006684: DW_TAG_subprogram
DW_AT_low_pc (0x00000000004013a0)
DW_AT_high_pc (0x00000000004013a8)
DW_AT_frame_base (DW_OP_reg7 RSP)
DW_AT_object_pointer (0x0000669c)
DW_AT_GNU_all_call_sites (true)
DW_AT_specification (0x00005b5c "_ZN6Object3fooE4test")

0x000066a5: DW_TAG_formal_parameter
DW_AT_name ("t")
DW_AT_decl_file ("/disk1/yifeng.dongyifeng/my_code/llvm/build/bin/coro-debug-1.cpp")
DW_AT_decl_line (48)
DW_AT_type (0x00004146 "test")

0x000066ba: DW_TAG_variable
DW_AT_name ("t")
DW_AT_type (0x00004146 "test")
DW_AT_artificial (true)
```
The elf also has two 't' in the same scope.
But unluckily, it might let the debugger
confused. And failed to print parameters for O0 or above.
This patch will make coroutine parameters and move
parameters use the same DIVar and try to fix the problems
that I mentioned before.

Test Plan: check-clang

Reviewed By: aprantl, jmorse

Differential Revision: https://reviews.llvm.org/D97533

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