function signature constraints are not a part of mangled name #49884

llvmbot · 2021-05-31T11:02:59Z


Bugzilla Link	50540
Version	11.0
OS	All
Reporter	LLVM Bugzilla Contributor
CC	@Dushistov,@zygoloid,@saarraz

Extended Description

$ cat b.cpp && echo EOFFFFFFFFFF

template <class> void foo() {} //1
void useFirst()
{
    foo<void>();// call 1 - instantiate "void foo<int>()"
}

template <class> void foo() requires true {} //2
void useSecond()
{
    foo<void>();// call 2 - instantiate "void foo<int>() requires true"
}

EOFFFFFFFFFF

$ clang++ -v -std=c++20 -c b.cpp
clang version 11.1.0
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/lib/llvm/11/bin
Selected GCC installation: /usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Selected multilib: .;@m64
 (in-process)
 "/usr/lib/llvm/11/bin/clang-11" -cc1 -triple x86_64-pc-linux-gnu -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -discard-value-names -main-file-name b.cpp -mrelocation-model static -mframe-pointer=all -fmath-errno -fno-rounding-math -mconstructor-aliases -munwind-tables -target-cpu x86-64 -fno-split-dwarf-inlining -debugger-tuning=gdb -v -resource-dir /usr/lib/llvm/11/bin/../../../../lib/clang/11.1.0 -internal-isystem /usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10 -internal-isystem /usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/x86_64-pc-linux-gnu -internal-isystem /usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/backward -internal-isystem /usr/local/include -internal-isystem /usr/lib/llvm/11/bin/../../../../lib/clang/11.1.0/include -internal-externc-isystem /include -internal-externc-isystem /usr/include -std=c++20 -fdeprecated-macro -fdebug-compilation-dir /home/vopl/tmp/15 -ferror-limit 19 -fgnuc-version=4.2.1 -fcxx-exceptions -fexceptions -fcolor-diagnostics -o b.o -x c++ b.cpp
clang -cc1 version 11.1.0 based upon LLVM 11.1.0 default target x86_64-pc-linux-gnu
ignoring nonexistent directory "/usr/local/include"
ignoring nonexistent directory "/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10
 /usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/x86_64-pc-linux-gnu
 /usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/backward
 /usr/lib/llvm/11/bin/../../../../lib/clang/11.1.0/include
 /usr/include
End of search list.
b.cpp:7:23: error: definition with same mangled name '_Z3fooIvEvv' as another definition
template <class> void foo() requires true {} //2
                      ^
b.cpp:1:23: note: previous definition is here
template <class> void foo() {} //1
                      ^
1 error generated.

My expectations: mangled names must be different, because mangled name is based on the signature and a signature includes the requires-clause as a part

llvmbot · 2021-05-31T11:07:51Z

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100825

llvmbot · 2021-06-04T08:55:19Z

itanium-cxx-abi/cxx-abi#24

shafik · 2023-09-20T17:02:26Z

@zygoloid it looks like the discussion on the ABI issue died out but on the gcc bug: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100825

you mentioned that you had an implementation ready, is that still the case?

llvmbot · 2023-09-20T17:11:05Z

@llvm/issue-subscribers-clang-codegen

| | | | --- | --- | | Bugzilla Link | [50540](https://llvm.org/bz50540) | | Version | 11.0 | | OS | All | | Reporter | LLVM Bugzilla Contributor | | CC | @dushistov,@zygoloid,@saarraz |

Extended Description

$ cat b.cpp && echo EOFFFFFFFFFF

template &lt;class&gt; void foo() {} //1
void useFirst()
{
    foo&lt;void&gt;();// call 1 - instantiate "void foo&lt;int&gt;()"
}

template &lt;class&gt; void foo() requires true {} //2
void useSecond()
{
    foo&lt;void&gt;();// call 2 - instantiate "void foo&lt;int&gt;() requires true"
}

EOFFFFFFFFFF

$ clang++ -v -std=c++20 -c b.cpp
clang version 11.1.0
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/lib/llvm/11/bin
Selected GCC installation: /usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0
Candidate multilib: .;@<!-- -->m64
Candidate multilib: 32;@<!-- -->m32
Selected multilib: .;@<!-- -->m64
 (in-process)
 "/usr/lib/llvm/11/bin/clang-11" -cc1 -triple x86_64-pc-linux-gnu -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -discard-value-names -main-file-name b.cpp -mrelocation-model static -mframe-pointer=all -fmath-errno -fno-rounding-math -mconstructor-aliases -munwind-tables -target-cpu x86-64 -fno-split-dwarf-inlining -debugger-tuning=gdb -v -resource-dir /usr/lib/llvm/11/bin/../../../../lib/clang/11.1.0 -internal-isystem /usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10 -internal-isystem /usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/x86_64-pc-linux-gnu -internal-isystem /usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/backward -internal-isystem /usr/local/include -internal-isystem /usr/lib/llvm/11/bin/../../../../lib/clang/11.1.0/include -internal-externc-isystem /include -internal-externc-isystem /usr/include -std=c++20 -fdeprecated-macro -fdebug-compilation-dir /home/vopl/tmp/15 -ferror-limit 19 -fgnuc-version=4.2.1 -fcxx-exceptions -fexceptions -fcolor-diagnostics -o b.o -x c++ b.cpp
clang -cc1 version 11.1.0 based upon LLVM 11.1.0 default target x86_64-pc-linux-gnu
ignoring nonexistent directory "/usr/local/include"
ignoring nonexistent directory "/include"
#include "..." search starts here:
#include &lt;...&gt; search starts here:
 /usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10
 /usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/x86_64-pc-linux-gnu
 /usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include/g++-v10/backward
 /usr/lib/llvm/11/bin/../../../../lib/clang/11.1.0/include
 /usr/include
End of search list.
b.cpp:7:23: error: definition with same mangled name '_Z3fooIvEvv' as another definition
template &lt;class&gt; void foo() requires true {} //2
                      ^
b.cpp:1:23: note: previous definition is here
template &lt;class&gt; void foo() {} //1
                      ^
1 error generated.

My expectations: mangled names must be different, because mangled name is based on the signature and a signature includes the requires-clause as a part

This implements proposals from: - itanium-cxx-abi/cxx-abi#24: mangling for constraints, requires-clauses, requires-expressions. - itanium-cxx-abi/cxx-abi#31: requires-clauses and template parameters in a lambda expression are mangled into the <lambda-sig>. - itanium-cxx-abi/cxx-abi#47 (STEP 3): mangling for template argument is prefixed by mangling of template parameter declaration if it's not "obvious", for example because the template parameter is constrained (we already implemented STEP 1 and STEP 2). This changes the manglings for a few cases: - Functions and function templates with constraints. - Function templates with template parameters with deduced types: `typename<auto N> void f();` - Function templates with template template parameters where the argument has a different template-head: `template<template<typename...T>> void f(); f<std::vector>();` In each case where a mangling changed, the change fixes a mangling collision. Note that only function templates are affected, not class templates or variable templates, and only new constructs (template parameters with deduced types, constrained templates) and esoteric constructs (templates with template template parameters with non-matching template template arguments, most of which Clang still does not accept by default due to `-frelaxed-template-template-args` not being enabled by default), so the risk to ABI stability from this change is relatively low. Nonetheless, `-fclang-abi-compat=17` can be used to restore the old manglings for cases which we could successfully but incorrectly mangle before. Fixes #48216, #49884, #61273 Reviewed By: erichkeane, #libc_abi Differential Revision: https://reviews.llvm.org/D147655

zygoloid · 2023-09-20T19:41:33Z

@zygoloid it looks like the discussion on the ABI issue died out but on the gcc bug: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100825

you mentioned that you had an implementation ready, is that still the case?

Yes, I've merged https://reviews.llvm.org/D147655 as 4b163e3, which fixes this issue. We now produce these symbols:

_Z3fooIvEvv for unconstrained foo<void>()
_Z3fooIvEvvQLb1E for foo<void>() requires true

shafik · 2023-09-20T19:49:22Z

Yes, I've merged https://reviews.llvm.org/D147655 as 4b163e3, which fixes this issue. We now produce these symbols:

_Z3fooIvEvv for unconstrained foo<void>()

_Z3fooIvEvvQLb1E for foo<void>() requires true

Excellent, does this also fix: #52951

zygoloid · 2023-09-20T20:07:10Z

Excellent, does this also fix: #52951

It does!

llvmbot transferred this issue from llvm/llvm-bugzilla-archive Dec 11, 2021

usx95 added this to C++ 20 in Clang Aug 21, 2022

shafik mentioned this issue Mar 9, 2023

Merged definitions of member functions distinguished by non-functionally-equivalent constraints and by deduced return type #61273

Closed

zygoloid self-assigned this Apr 7, 2023

shafik mentioned this issue Sep 20, 2023

Static and non-static member function templates with the same parameter types are accepted #52951

Closed

Endilll added the clang:codegen IR generation bugs: mangling, exceptions, etc. label Sep 20, 2023

zygoloid closed this as completed Sep 20, 2023

github-project-automation bot moved this to Done in C++ 20 in Clang Sep 20, 2023

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function signature constraints are not a part of mangled name #49884

function signature constraints are not a part of mangled name #49884

llvmbot commented May 31, 2021 •

edited by shafik

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llvmbot commented May 31, 2021

llvmbot commented Jun 4, 2021

shafik commented Sep 20, 2023

llvmbot commented Sep 20, 2023

Extended Description

zygoloid commented Sep 20, 2023

shafik commented Sep 20, 2023

zygoloid commented Sep 20, 2023

function signature constraints are not a part of mangled name #49884

function signature constraints are not a part of mangled name #49884

Comments

llvmbot commented May 31, 2021 • edited by shafik Loading

Extended Description

llvmbot commented May 31, 2021

llvmbot commented Jun 4, 2021

shafik commented Sep 20, 2023

llvmbot commented Sep 20, 2023

Extended Description

zygoloid commented Sep 20, 2023

shafik commented Sep 20, 2023

zygoloid commented Sep 20, 2023

llvmbot commented May 31, 2021 •

edited by shafik

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