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cor3ntin opened this issue Jun 6, 2023 · 3 comments · Fixed by #95474
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Implement P2280R4 Using unknown pointers and references in constant expressions #63139

cor3ntin opened this issue Jun 6, 2023 · 3 comments · Fixed by #95474
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c++23 clang:frontend Language frontend issues, e.g. anything involving "Sema"

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@cor3ntin
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cor3ntin commented Jun 6, 2023

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@cor3ntin cor3ntin added clang:frontend Language frontend issues, e.g. anything involving "Sema" c++23 labels Jun 6, 2023
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llvmbot commented Jun 6, 2023

@llvm/issue-subscribers-clang-frontend

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llvmbot commented Jun 6, 2023

@llvm/issue-subscribers-c-2b

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@frederick-vs-ja frederick-vs-ja mentioned this issue Aug 3, 2023
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@cor3ntin cor3ntin mentioned this issue Oct 4, 2023
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@shafik shafik mentioned this issue Feb 26, 2024
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@shafik shafik self-assigned this Mar 4, 2024
@shafik shafik mentioned this issue Mar 4, 2024
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KyunLFA commented Apr 6, 2024

Valve's Gamescope on git HEAD does not build anymore due to this error if my (limited) understanding is correct.

GCC passes, Clang doesn't.

FAILED: src/gamescope.p/wayland_backend.cpp.o 
/usr/bin/clang++ -Isrc/gamescope.p -Isrc -I../gamescope/src -I../gamescope/src/reshade/source -I../gamescope/src/reshade/include -I../gamescope/thirdparty/SPIRV-Headers/include/spirv/unified1 -Isubprojects/glm -I../gamescope/subprojects/glm -Isubprojects/reshade -I../gamescope/subprojects/reshade -Isubprojects/wlroots/include -I../gamescope/subprojects/wlroots/include -I../gamescope/subprojects/libdisplay-info/include -I../gamescope/subprojects/libliftoff/include -Isubprojects/stb -I../gamescope/subprojects/stb -Iprotocol -I/usr/include/libdrm -I/usr/include/SDL2 -I/usr/include/pixman-1 -I/usr/include/uuid -I/usr/include/pipewire-0.3 -I/usr/include/spa-0.2 -I/usr/include/openvr -I/usr/include/libdecor-0 -fdiagnostics-color=always -D_GLIBCXX_ASSERTIONS=1 -D_LIBCPP_HARDENING_MODE=_LIBCPP_HARDENING_MODE_EXTENSIVE -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -Wextra -std=c++20 -DWLR_USE_UNSTABLE -Wno-unused-parameter -Wno-missing-field-initializers -Wno-c99-designator -Wno-invalid-offsetof -Wno-unused-const-variable -Wno-deprecated-volatile -Wno-ignored-qualifiers -Wno-missing-braces -ffast-math -DHAVE_PIPEWIRE=1 -DHAVE_OPENVR=1 '-DHWDATA_PNP_IDS="//usr/share/hwdata/pnp.ids"' -flto=full -march=znver4 -O3 -pipe -fno-plt -fexceptions -Wp,-D_FORTIFY_SOURCE=3 -Wformat -Werror=format-security -fstack-protector-all -fcf-protection -fno-semantic-interposition -Wno-unused-command-line-argument -mllvm -polly -fwhole-program-vtables -Wp,-D_GLIBCXX_ASSERTIONS -fPIE -DAVIF_DLL -isystem/usr/include/libdrm -D_REENTRANT -pthread -DHAVE_DRM=1 -DHAVE_SDL2=1 -DHAVE_AVIF=1 -DHAVE_LIBCAP=1 -MD -MQ src/gamescope.p/wayland_backend.cpp.o -MF src/gamescope.p/wayland_backend.cpp.o.d -o src/gamescope.p/wayland_backend.cpp.o -c ../gamescope/src/wayland_backend.cpp
In file included from ../gamescope/src/wayland_backend.cpp:1:
In file included from ../gamescope/src/backend.h:7:
../gamescope/src/rc.h:171:36: error: constexpr if condition is not a constant expression
  171 |                     if constexpr ( m_pObject->ReferenceOwnsObject() )
      |                                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../gamescope/src/rc.h:140:19: note: in instantiation of member function 'gamescope::Rc<gamescope::CWaylandFb>::DecRef' requested here
  140 |             this->DecRef();
      |                   ^
../gamescope/src/wayland_backend.cpp:1111:22: note: in instantiation of member function 'gamescope::Rc<gamescope::CWaylandFb>::~Rc' requested here
 1111 |     CWaylandBackend::CWaylandBackend()
      |                      ^
../gamescope/src/rc.h:171:36: note: implicit use of 'this' pointer is only allowed within the evaluation of a call to a 'constexpr' member function
  171 |                     if constexpr ( m_pObject->ReferenceOwnsObject() )
      |                                    ^
../gamescope/src/rc.h:171:36: error: constexpr if condition is not a constant expression
  171 |                     if constexpr ( m_pObject->ReferenceOwnsObject() )
      |                                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../gamescope/src/rc.h:140:19: note: in instantiation of member function 'gamescope::Rc<gamescope::IBackendFb>::DecRef' requested here
  140 |             this->DecRef();
      |                   ^
../gamescope/src/wayland_backend.cpp:1231:69: note: in instantiation of member function 'gamescope::Rc<gamescope::IBackendFb>::~Rc' requested here
 1231 |             m_BlackFb = static_cast<CWaylandFb *>( m_pBlackTexture->GetBackendFb().get() );
      |                                                                     ^
../gamescope/src/rc.h:171:36: note: implicit use of 'this' pointer is only allowed within the evaluation of a call to a 'constexpr' member function
  171 |                     if constexpr ( m_pObject->ReferenceOwnsObject() )
      |                                    ^
2 errors generated.

Full context: https://github.com/ValveSoftware/gamescope/blob/master/src/rc.h

Tested on CachyOS (Arch) Linux, LLVM 19.0.0 1c683eb. (Workaround suggestions (besides switching compilers) appreciated)

@KyunLFA KyunLFA mentioned this issue Apr 6, 2024
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@shafik shafik mentioned this issue Jun 13, 2024
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@shafik shafik mentioned this issue Jul 3, 2024
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shafik added a commit to shafik/llvm-project that referenced this issue Jul 17, 2024
@shafik
[Clang] Implement P2280R4 Using unknown pointers and references in co…
69b09ea 
…nstant expressions

P2280R4 allows the use of references in pointers of unknown origins in a
constant expression context but only in specific cases that could be constant
expressions.

We track whether a variable is a constexpr unknown in a constant expression by
setting a flag in either APValue or LValue and using this flag to prevent using
unknown values in places where it is not allowed.

In `evaluateVarDeclInit` we may need to create a new `APValue` to track the
unknown referene or pointer and we track that `APValue` in the
`CallStackFrame`.

Fixes: llvm#63139
llvm#63117
@cor3ntin cor3ntin mentioned this issue Aug 20, 2024
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@frederick-vs-ja frederick-vs-ja mentioned this issue Aug 23, 2024
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@naav naav mentioned this issue Aug 29, 2024
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@MitalAshok MitalAshok mentioned this issue Sep 4, 2024
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@efriedma-quic efriedma-quic mentioned this issue Oct 29, 2024
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jktjkt added a commit to CESNET/velia that referenced this issue Nov 19, 2024
@jktjkt
hardware: adjust voltage tolerances
ad7c850 
On one board, the 3V3 channel was constantly measuring 3.406V. This was
below our threshold, so I tried to identify what the actual standard
tolerances are. In the ATX specification version 2.2 [1] (unofficial
link because the official (?) formfactors.org now redirects to an Intel
page which says nope, nothing here), all tolerances for positive
voltages are specified as ±5%.

Let's use that for the warning threshold everywhere (because this is a
standard, anything that's within the allowed range is by definition OK).

We also have to account for the tolerance of the actual measurement. The
PSU's specification says [2, page 27] that (during our typical load,
which fits into the 10%-20% range), the measurements have a ±5%
tolerance. So it's "possible" that we have, say, a perfectly valid
voltage of 5.25V (which is within 5% of the 5V target) measured by an
inaccurate sensor, yielding a 5.5125V. This shall be our "critical"
threshold.

Let's wrap this in a shiny function as Tomas suggested. I also wanted to
add something like:

 static_assert(nominal > hysteresis * 10, "these units look very suspicious");

...but clang rejects this, probably due to [3].

TL;DR: a critical voltage alarm now means that the power is seriously
hosed. A warning might still be a false positive when the tolerances are
not aligned properly.

[1] https://cdn.instructables.com/ORIG/FS8/5ILB/GU59Z1AT/FS85ILBGU59Z1AT.pdf
[2] CzechLight/hw-docs, components/power/YH5151-1EB01R-Spec.pdf
[3] llvm/llvm-project#63139

Change-Id: Iad2e06ede62d82b5b338e8486224d85850d7c018
@frederick-vs-ja frederick-vs-ja mentioned this issue Nov 29, 2024
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@cor3ntin cor3ntin mentioned this issue Jan 15, 2025
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github-actions bot pushed a commit to arm/arm-toolchain that referenced this issue Jan 22, 2025
@shafik @github-actions
Automerge: [Clang] Implement P2280R4 Using unknown pointers and refer…
90795c3 
…ences in constant expressions (#95474)

P2280R4 allows the use of references in pointers of unknown origins in a
constant expression context but only in specific cases that could be
constant expressions.

We track whether a variable is a constexpr unknown in a constant
expression by setting a flag in either APValue or LValue and using this
flag to prevent using unknown values in places where it is not allowed.

Fixes: llvm/llvm-project#63139 llvm/llvm-project#63117
@abellgithub abellgithub mentioned this issue Mar 3, 2025
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@frederick-vs-ja frederick-vs-ja mentioned this issue Mar 21, 2025
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