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@broadwaylamb
Created April 27, 2020 19:37
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A bug in the LLVM implementation of the divtf3 builtin (aarch64-linux-gnu)
#include <iostream>
#include <ios>
#include <iomanip>
#include <cstdint>
#include <cstring>
#include <cassert>
#include <limits>
// If this file is compiled and linked against libgcc, it runs just fine.
// If it is linked against compiler-rt builtins, the assertion fails.
// target: aarch64-linux-gnu
extern "C" long double __divtf3(long double a, long double b);
int main() {
long double result = __divtf3(std::numeric_limits<long double>::min(), 2.0L);
uint8_t expected[sizeof(long double)] = { 0x00,
0x00,
0x00,
0x00,
0x00,
0x00,
0x00,
0x00,
0x00,
0x00,
0x00,
0x00,
0x00,
0x80,
0x00,
0x00 };
uint8_t actual[sizeof(long double)];
memcpy(actual, &result, sizeof(long double));
std::cout << "__LDBL_MIN__ / 2.0L = " << result
<< ", bit pattern: ";
for (size_t i = 0; i < sizeof(actual); ++i) {
std::cout << std::hex << std::setfill('0') << std::setw(2)
<< (int)actual[i] << ' ';
}
std::cout << std::endl;
assert(memcmp(expected, actual, sizeof(long double)) == 0);
return 0;
}
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