| Issue |
76684
|
| Summary |
Clang considers the non-default variant of a multiversioned function unused
|
| Labels |
clang
|
| Assignees |
|
| Reporter |
nabijaczleweli
|
repro.cpp:
```cpp
#include <cstdint>
#include <cstdio>
#include <cstring>
#include <sys/mman.h>
#include <unistd.h>
#if __i386__ || __x86_64__
#include <nmmintrin.h>
#else
#error
#endif
namespace {
__attribute__((target("default"))) std::uint32_t crc32c(std::uint32_t cur, const void * data, std::size_t data_len) {
static const constexpr std::uint32_t crc_lut[] = {
0x00000000, 0xF26B8303, 0xE13B70F7, 0x1350F3F4, 0xC79A971F, 0x35F1141C, 0x26A1E7E8, 0xD4CA64EB, 0x8AD958CF, 0x78B2DBCC, 0x6BE22838, 0x9989AB3B,
0x4D43CFD0, 0xBF284CD3, 0xAC78BF27, 0x5E133C24, 0x105EC76F, 0xE235446C, 0xF165B798, 0x030E349B, 0xD7C45070, 0x25AFD373, 0x36FF2087, 0xC494A384,
0x9A879FA0, 0x68EC1CA3, 0x7BBCEF57, 0x89D76C54, 0x5D1D08BF, 0xAF768BBC, 0xBC267848, 0x4E4DFB4B, 0x20BD8EDE, 0xD2D60DDD, 0xC186FE29, 0x33ED7D2A,
0xE72719C1, 0x154C9AC2, 0x061C6936, 0xF477EA35, 0xAA64D611, 0x580F5512, 0x4B5FA6E6, 0xB93425E5, 0x6DFE410E, 0x9F95C20D, 0x8CC531F9, 0x7EAEB2FA,
0x30E349B1, 0xC288CAB2, 0xD1D83946, 0x23B3BA45, 0xF779DEAE, 0x05125DAD, 0x1642AE59, 0xE4292D5A, 0xBA3A117E, 0x4851927D, 0x5B016189, 0xA96AE28A,
0x7DA08661, 0x8FCB0562, 0x9C9BF696, 0x6EF07595, 0x417B1DBC, 0xB3109EBF, 0xA0406D4B, 0x522BEE48, 0x86E18AA3, 0x748A09A0, 0x67DAFA54, 0x95B17957,
0xCBA24573, 0x39C9C670, 0x2A993584, 0xD8F2B687, 0x0C38D26C, 0xFE53516F, 0xED03A29B, 0x1F682198, 0x5125DAD3, 0xA34E59D0, 0xB01EAA24, 0x42752927,
0x96BF4DCC, 0x64D4CECF, 0x77843D3B, 0x85EFBE38, 0xDBFC821C, 0x2997011F, 0x3AC7F2EB, 0xC8AC71E8, 0x1C661503, 0xEE0D9600, 0xFD5D65F4, 0x0F36E6F7,
0x61C69362, 0x93AD1061, 0x80FDE395, 0x72966096, 0xA65C047D, 0x5437877E, 0x4767748A, 0xB50CF789, 0xEB1FCBAD, 0x197448AE, 0x0A24BB5A, 0xF84F3859,
0x2C855CB2, 0xDEEEDFB1, 0xCDBE2C45, 0x3FD5AF46, 0x7198540D, 0x83F3D70E, 0x90A324FA, 0x62C8A7F9, 0xB602C312, 0x44694011, 0x5739B3E5, 0xA55230E6,
0xFB410CC2, 0x092A8FC1, 0x1A7A7C35, 0xE811FF36, 0x3CDB9BDD, 0xCEB018DE, 0xDDE0EB2A, 0x2F8B6829, 0x82F63B78, 0x709DB87B, 0x63CD4B8F, 0x91A6C88C,
0x456CAC67, 0xB7072F64, 0xA457DC90, 0x563C5F93, 0x082F63B7, 0xFA44E0B4, 0xE9141340, 0x1B7F9043, 0xCFB5F4A8, 0x3DDE77AB, 0x2E8E845F, 0xDCE5075C,
0x92A8FC17, 0x60C37F14, 0x73938CE0, 0x81F80FE3, 0x55326B08, 0xA759E80B, 0xB4091BFF, 0x466298FC, 0x1871A4D8, 0xEA1A27DB, 0xF94AD42F, 0x0B21572C,
0xDFEB33C7, 0x2D80B0C4, 0x3ED04330, 0xCCBBC033, 0xA24BB5A6, 0x502036A5, 0x4370C551, 0xB11B4652, 0x65D122B9, 0x97BAA1BA, 0x84EA524E, 0x7681D14D,
0x2892ED69, 0xDAF96E6A, 0xC9A99D9E, 0x3BC21E9D, 0xEF087A76, 0x1D63F975, 0x0E330A81, 0xFC588982, 0xB21572C9, 0x407EF1CA, 0x532E023E, 0xA145813D,
0x758FE5D6, 0x87E466D5, 0x94B49521, 0x66DF1622, 0x38CC2A06, 0xCAA7A905, 0xD9F75AF1, 0x2B9CD9F2, 0xFF56BD19, 0x0D3D3E1A, 0x1E6DCDEE, 0xEC064EED,
0xC38D26C4, 0x31E6A5C7, 0x22B65633, 0xD0DDD530, 0x0417B1DB, 0xF67C32D8, 0xE52CC12C, 0x1747422F, 0x49547E0B, 0xBB3FFD08, 0xA86F0EFC, 0x5A048DFF,
0x8ECEE914, 0x7CA56A17, 0x6FF599E3, 0x9D9E1AE0, 0xD3D3E1AB, 0x21B862A8, 0x32E8915C, 0xC083125F, 0x144976B4, 0xE622F5B7, 0xF5720643, 0x07198540,
0x590AB964, 0xAB613A67, 0xB831C993, 0x4A5A4A90, 0x9E902E7B, 0x6CFBAD78, 0x7FAB5E8C, 0x8DC0DD8F, 0xE330A81A, 0x115B2B19, 0x020BD8ED, 0xF0605BEE,
0x24AA3F05, 0xD6C1BC06, 0xC5914FF2, 0x37FACCF1, 0x69E9F0D5, 0x9B8273D6, 0x88D28022, 0x7AB90321, 0xAE7367CA, 0x5C18E4C9, 0x4F48173D, 0xBD23943E,
0xF36E6F75, 0x0105EC76, 0x12551F82, 0xE03E9C81, 0x34F4F86A, 0xC69F7B69, 0xD5CF889D, 0x27A40B9E, 0x79B737BA, 0x8BDCB4B9, 0x988C474D, 0x6AE7C44E,
0xBE2DA0A5, 0x4C4623A6, 0x5F16D052, 0xAD7D5351};
auto bytes = reinterpret_cast<const std::uint8_t *>(data), end = bytes + data_len;
for(; bytes != end; ++bytes)
cur = (cur >> 8) ^ crc_lut[(cur & 0xFF) ^ *bytes];
return cur;
}
#if __i386__ || __x86_64__
__attribute__((target("sse4.2"))) std::uint32_t crc32c(std::uint32_t cur_r, const void * data, std::size_t data_len) {
#if __x86_64__ // this isn't a simple std::size_t+#if _LP64 because x32 is amd64 ILP32
using sse42_t = std::uint64_t;
#define _mm_crc32_big _mm_crc32_u64
#else
using sse42_t = std::uint32_t;
#define _mm_crc32_big _mm_crc32_u32
#endif
sse42_t cur = cur_r;
auto bulk_iter = reinterpret_cast<const sse42_t *>(data);
for(auto bulk = data_len / sizeof(sse42_t); bulk; --bulk, ++bulk_iter)
cur = _mm_crc32_big(cur, *bulk_iter);
auto single_iter = reinterpret_cast<const std::uint8_t *>(bulk_iter);
for(auto single = data_len % sizeof(sse42_t); single; --single, ++single_iter)
cur = _mm_crc32_u8(cur, *single_iter);
return cur;
}
#endif
}
int main() {
auto m = mmap(nullptr, 1024ull * 1024 * 1024 , PROT_READ, MAP_PRIVATE | MAP_ANONYMOUS | MAP_POPULATE, -1, 0);
int ret{};
for(int i = 0; i < 1000; ++i)
ret ^= crc32c(~0, m, 1024ull * 1024 * 1024 );
std::printf("%08x\n", ret);
}
```
```
$ c++ -O3 -g -Wall -Wextra -fno-exceptions -fno-rtti -std=c++20 -D_FILE_OFFSET_BITS=64 -DTEXTDOMAIN_DIRNAME='"/usr/local/share/locale"' repro.cpp -o repro
repro.cpp:16:50: warning: unused function 'crc32c' [-Wunused-function]
16 | __attribute__((target("sse4.2"))) std::uint32_t crc32c(std::uint32_t cur_r, const void * data, std::size_t data_len) {
| ^~~~~~
1 warning generated.
```
with
```
$ c++ --version
Debian clang version 18.0.0 (++20231231112334+c7c912cff945-1~exp1~20231231112352.433)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /bin
```
GCC 12.2.0-14 correctly doesn't warn about this.
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