Describe the bug
Passing volatile pointers to fill with arguments that satisfy _Fill_memset_is_safe will fail to compile, as that branch calls memset which cannot take volatile pointers.
Command-line test case
E:\Temp>type repro.cpp
#include <cstdlib>
#include <iostream>
#include <algorithm>
void memzero(void* a_dst, std::size_t a_size)
{
const auto beg = static_cast<volatile char*>(a_dst);
const auto end = static_cast<volatile char*>(a_dst) + a_size;
constexpr char val = 0;
std::fill(beg, end, val);
}
int main()
{
int num = 42;
std::cout << num << '\n';
memzero(&num, sizeof(num));
std::cout << num << '\n';
}
E:\Temp>cl /EHsc /W4 /WX .\repro.cpp
Microsoft (R) C/C++ Optimizing Compiler Version 19.28.29115 for x64
Copyright (C) Microsoft Corporation. All rights reserved.
repro.cpp
C:\Program Files (x86)\Microsoft Visual Studio\2019\Preview\VC\Tools\MSVC\14.28.29115\include\xutility(4717): error C2664: 'void *memset(void *,int,size_t)': cannot convert argument 1 from '_FwdIt' to 'void *'
with
[
_FwdIt=volatile char *
]
C:\Program Files (x86)\Microsoft Visual Studio\2019\Preview\VC\Tools\MSVC\14.28.29115\include\xutility(4717): note: Conversion loses qualifiers
C:\Program Files (x86)\Microsoft Visual Studio\2019\Preview\VC\Tools\MSVC\14.28.29115\include\vcruntime_string.h(63): note: see declaration of 'memset'
.\repro.cpp(10): note: see reference to function template instantiation 'void std::fill<volatile char*,char>(const _FwdIt,const _FwdIt,const _Ty &)' being compiled
with
[
_FwdIt=volatile char *,
_Ty=char
]
Expected behavior
The program should compile.
STL version
Microsoft Visual Studio Community 2019 Preview
Version 16.8.0 Preview 1.0
Additional context
Both GCC and Clang can compile this example, here's a godbolt link.
It will actually compile if you use std::fill(beg, end, 0); presumably because _Ty is now int and _Fill_memset_is_safe evaluates to false.
Describe the bug
Passing volatile pointers to
fillwith arguments that satisfy_Fill_memset_is_safewill fail to compile, as that branch callsmemsetwhich cannot take volatile pointers.Command-line test case
Expected behavior
The program should compile.
STL version
Additional context
Both GCC and Clang can compile this example, here's a godbolt link.
It will actually compile if you use
std::fill(beg, end, 0);presumably because_Tyis nowintand_Fill_memset_is_safeevaluates to false.