From 56048f9718d1104227795a23c02fa144543c07d0 Mon Sep 17 00:00:00 2001 From: Julian Waters Date: Thu, 1 Dec 2022 04:21:52 +0000 Subject: [PATCH] 8297852: Backout 8252584 for the time being Reviewed-by: kbarrett --- doc/hotspot-style.html | 49 +----------------------------------------- doc/hotspot-style.md | 47 +--------------------------------------- 2 files changed, 2 insertions(+), 94 deletions(-) diff --git a/doc/hotspot-style.html b/doc/hotspot-style.html index 939c427b95c..6aa6047ede9 100644 --- a/doc/hotspot-style.html +++ b/doc/hotspot-style.html @@ -72,7 +72,6 @@ Deduction
  • Expression SFINAE
  • enum
    • -
  • alignas
  • thread_local
  • nullptr
  • <atomic>
    • @@ -599,7 +598,7 @@ conventions might appear jarring and reduce readability.

    std::numeric_limits.
  • #include <type_traits>.
  • #include <cstddef> to use -std::nullptr_t and std::max_align_t.
    • +std::nullptr_t.

    TODO: Rather than directly #including (permitted) Standard Library headers, use a convention of #including wrapper headers (in some @@ -671,52 +670,6 @@ of enums and avoidance of in-class initialization of static integral constant members. Compilers having such bugs are no longer supported. Except where an enum is semantically appropriate, new code should use integral constants.

    -

    alignas

    -

    Alignment-specifiers (alignas n2341) -are permitted, with restrictions.

    -

    Alignment-specifiers are permitted when the requested -alignment is a fundamental alignment (not greater than -alignof(std::max_align_t) C++14 -3.11/2).

    -

    Alignment-specifiers with an extended alignment -(greater than alignof(std::max_align_t) C++14 -3.11/3) may only be used to align variables with static or automatic -storage duration (C++14 -3.7.1, 3.7.3). As a consequence, over-aligned types are -forbidden; this may change if HotSpot updates to using C++17 or later p0035r4.

    -

    Large extended alignments should be avoided, particularly -for stack allocated objects. What is a large value may depend on the -platform and configuration. There may also be hard limits for some -platforms.

    -

    An alignment-specifier must always be applied to a -definition (C++14 -10.6.2/6). (C++ allows an alignment-specifier to optionally -also be applied to a declaration, so long as the definition has -equivalent alignment. There isn't any known benefit from duplicating the -alignment in a non-definition declaration, so such duplication should be -avoided in HotSpot code.)

    -

    Enumerations are forbidden from having alignment-specifiers. -Aligned enumerations were originally permitted but insufficiently -specified, and were later (C++20) removed CWG 2354. -Permitting such usage in HotSpot now would just cause problems in the -future.

    -

    Alignment-specifiers are forbidden in typedef -and alias-declarations. This may work or may have worked in -some versions of some compilers, but was later (C++14) explicitly -disallowed CWG -1437.

    -

    The HotSpot macro ATTRIBUTE_ALIGNED provides similar -capabilities for platforms that define it. This macro predates the use -by HotSpot of C++ versions providing alignas. New code -should use alignas.

    thread_local

    Avoid use of thread_local (n2659); diff --git a/doc/hotspot-style.md b/doc/hotspot-style.md index 8d09855c78c..eeb9d21e74c 100644 --- a/doc/hotspot-style.md +++ b/doc/hotspot-style.md @@ -573,7 +573,7 @@ There are a few exceptions to this rule. * `#include ` to use placement `new`, `std::nothrow`, and `std::nothrow_t`. * `#include ` to use `std::numeric_limits`. * `#include `. -* `#include ` to use `std::nullptr_t` and `std::max_align_t`. +* `#include ` to use `std::nullptr_t`. TODO: Rather than directly \#including (permitted) Standard Library headers, use a convention of \#including wrapper headers (in some @@ -651,51 +651,6 @@ constant members. Compilers having such bugs are no longer supported. Except where an enum is semantically appropriate, new code should use integral constants. -### alignas - -_Alignment-specifiers_ (`alignas` -[n2341](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2341.pdf)) -are permitted, with restrictions. - -_Alignment-specifiers_ are permitted when the requested alignment is a -_fundamental alignment_ (not greater than `alignof(std::max_align_t)` -[C++14 3.11/2](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4296.pdf)). - -_Alignment-specifiers_ with an _extended alignment_ (greater than -`alignof(std::max_align_t)` -[C++14 3.11/3](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4296.pdf)) -may only be used to align variables with static or automatic storage duration -([C++14 3.7.1, 3.7.3](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4296.pdf)). -As a consequence, _over-aligned types_ are forbidden; this may change if -HotSpot updates to using C++17 or later -[p0035r4](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0035r4.html). - -Large _extended alignments_ should be avoided, particularly for stack -allocated objects. What is a large value may depend on the platform and -configuration. There may also be hard limits for some platforms. - -An _alignment-specifier_ must always be applied to a definition -([C++14 10.6.2/6](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4296.pdf)). -(C++ allows an _alignment-specifier_ to optionally also be applied to a -declaration, so long as the definition has equivalent alignment. There isn't -any known benefit from duplicating the alignment in a non-definition -declaration, so such duplication should be avoided in HotSpot code.) - -Enumerations are forbidden from having _alignment-specifiers_. Aligned -enumerations were originally permitted but insufficiently specified, and were -later (C++20) removed -[CWG 2354](https://cplusplus.github.io/CWG/issues/2354.html). -Permitting such usage in HotSpot now would just cause problems in the future. - -_Alignment-specifiers_ are forbidden in `typedef` and _alias-declarations_. -This may work or may have worked in some versions of some compilers, but was -later (C++14) explicitly disallowed -[CWG 1437](https://cplusplus.github.io/CWG/issues/1437.html). - -The HotSpot macro `ATTRIBUTE_ALIGNED` provides similar capabilities for -platforms that define it. This macro predates the use by HotSpot of C++ -versions providing `alignas`. New code should use `alignas`. - ### thread_local Avoid use of `thread_local`