Fixes https://github.com/llvm/llvm-project/issues/140149

Generate nuw GEPs for struct member accesses, as inbounds + non-negative
implies nuw.

Regression tests are updated using update scripts where possible, and by
find + replace where not.

This is a follow-up from the conversation starting at
https://github.com/llvm/llvm-project/pull/93809#issuecomment-2173729801

The root problem that motivated the change are external AST sources that
compute `ASTRecordLayout`s themselves instead of letting Clang compute
them from the AST. One such example is LLDB using DWARF to get the
definitive offsets and sizes of C++ structures. Such layouts should be
considered correct (modulo buggy DWARF), but various assertions and
lowering logic around the `CGRecordLayoutBuilder` relies on the AST
having `[[no_unique_address]]` attached to them. This is a
layout-altering attribute which is not encoded in DWARF. This causes us
LLDB to trip over the various LLVM<->Clang layout consistency checks.
There has been precedent for avoiding such layout-altering attributes
from affecting lowering with externally-provided layouts (e.g., packed
structs).

This patch proposes to replace the `isZeroSize` checks in
`CGRecordLayoutBuilder` (which roughly means "empty field with
[[no_unique_address]]") with checks for
`CodeGen::isEmptyField`/`CodeGen::isEmptyRecord`.

**Details**
The main strategy here was to change the `isZeroSize` check in
`CGRecordLowering::accumulateFields` and
`CGRecordLowering::accumulateBases` to use the `isEmptyXXX` APIs
instead, preventing empty fields from being added to the `Members` and
`Bases` structures. The rest of the changes fall out from here, to
prevent lookups into these structures (for field numbers or base
indices) from failing.

Added `isEmptyRecordForLayout` and `isEmptyFieldForLayout` (open to
better naming suggestions). The main difference to the existing
`isEmptyRecord`/`isEmptyField` APIs, is that the `isEmptyXXXForLayout`
counterparts don't have special treatment for `unnamed bitfields`/arrays
and also treat fields of empty types as if they had
`[[no_unique_address]]` (i.e., just like the `AsIfNoUniqueAddr` in
`isEmptyField` does).

This makes codegen for array initialization simpler in two ways:
1. Drop the zero-index GEP at the start, which is no longer needed with
opaque pointers.
2. Emit GEPs directly to the correct element, instead of having a long
chain of +1 GEPs. This is more canonical, and also avoids regressions in
unoptimized builds from #93823.

This bug is caused by parenthesized list initialization not being
implemented in `CodeGenFunction::EmitNewArrayInitializer(...)`.

Parenthesized list initialization of `struct`s with `operator new`
already works in Clang and is not affected by this bug.

Additionally, fix the test new-delete.cpp as it incorrectly assumes that
using parentheses with operator new to initialize arrays is illegal for
C++ versions >= C++17.

Fixes #68198

Set the writable and dead_on_unwind attributes for sret arguments. These
indicate that the argument points to writable memory (and it's legal to
introduce spurious writes to it on entry to the function) and that the
argument memory will not be used if the call unwinds.

This enables additional MemCpyOpt/DSE/LICM optimizations.

Before this patch, initialized class members would have the LifetimeKind
LK_MemInitializer, which does not allow for binding a temporary to a
reference. Binding to a temporary however is allowed in parenthesized
aggregate initialization, even if it leads to a dangling reference. To
fix this, we create a new EntityKind, EK_ParenAggInitMember, which has
LifetimeKind LK_FullExpression.

This patch does *not* attempt to diagnose dangling references as a
result of using this feature.

This patch also refactors TryOrBuildParenListInitialization(...) to
accomodate creating different InitializedEntity objects.

Fixes #61567

[0]: https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p0960r3.html

Reviewed By: shafik

Differential Revision: https://reviews.llvm.org/D148274

Previously, when checking whether an in-class initializer exists when
performing parenthesized aggregate initialization, Clang checks that the
output of FieldDecl::getInClassInitializer() is non-null. This is
incorrect; if the field is part of a templated type, then
getInClassInitializer() will return nullptr if we haven't called
Sem::BuildCXXDefaultInitExpr(...) before, even if
FieldDecl::hasInClassInitializer() returns true. The end result is that
Clang incorrectly ignores the in class initializer and
value-initializes the field. The fix therefore is to instead call
FieldDecl::hasInClassInitializer(), which is what we do for braced init
lists [0].

Before this patch, Clang does correctly recognize the in-class field
initializer in certain cases. This is Sema::BuildCXXDefaultInitExpr(...)
populates the in class initializer of the corresponding FieldDecl
object. Therefore, if that method was previously called with the same
FieldDecl object, as can happen with a decltype(...) or a braced list
initialization, FieldDecl::getInClassInitializer() will return a
non-null expression, and the field becomes properly initialized.

Fixes 62266

[0]: https://github.com/llvm/llvm-project/blob/be5f35e24f4c15caf3c4aeccddc54c52560c28a0/clang/lib/Sema/SemaInit.cpp#L685

Reviewed By: shafik

Differential Revision: https://reviews.llvm.org/D149389

* Fix an issue where temporaries initialized via parenthesized aggregate
  initialization don't get destroyed.
* Fix an issue where aggregate initialization omits calls to class
  members' move constructors after a TreeTransform. This occurs because
  the CXXConstructExpr wrapping the call to the move constructor gets
  unboxed during a TreeTransform of the wrapping FunctionalCastExpr (as with a
  InitListExpr), but unlike InitListExpr, we dont reperform the
  InitializationSequence for the list's expressions to regenerate the
  CXXConstructExpr. This patch fixes this bug by treating
  CXXParenListInitExpr identically to InitListExpr in this regard.

Fixes #61145

Reviewed By: rsmith

Differential Revision: https://reviews.llvm.org/D146465

This commit relands the patches for implementing P0960R3 and P1975R0,
which describe initializing aggregates via a parenthesized list.

The relanded commits are:

* 40c52159d3ee - P0960R3 and P1975R0: Allow initializing aggregates from
  a parenthesized list of values
* c77a91bb7ba7 - Remove overly restrictive aggregate paren init logic
* 32d7aae04fdb - Fix a clang crash on invalid code in C++20 mode

This patch also fixes a crash in the original implementation.
Previously, if the input tried to call an implicitly deleted copy or
move constructor of a union, we would then try to initialize the union
by initializing it's first element with a reference to a union. This
behavior is incorrect (we should fail to initialize) and if the type of
the first element has a constructor with a single template typename
parameter, then Clang will explode. This patch fixes that issue by
checking that constructor overload resolution did not result in a
deleted function before attempting parenthesized aggregate
initialization.

Additionally, this patch also includes D140159, which contains some
minor fixes made in response to code review comments in the original
implementation that were made after that patch was submitted.

Co-authored-by: Sheng <ox59616e@gmail.com>

Fixes #54040, Fixes #59675

Reviewed By: ilya-biryukov

Differential Revision: https://reviews.llvm.org/D141546