On Monday, 27 January 2025 at 05:53:09 UTC, John C. wrote:
On Sunday, 26 January 2025 at 16:43:19 UTC, Johan wrote:
The `align(32)` applies to the slice `a`, not the contents of
`a` (where `a` points to).
Thank you, seems that it is reason for that errors. I remember
that dynamic array can be represented as structure with size_t
len and pointer to memory location, so do we need to align
memory for this memory location, not dynamic array? Even if we
align dynamic array structure, we get five zeros at the end of
it's address, but memory location pointed to is still
unaligned, so do I have align it manually?
Exactly.
Does it work when you create an array of `float8`? (`float8[]
a = new float8[128/8];`)
No, I have modified original code version and errors are the
same, except for dmd with "-mcpu=avx" flag set (error changed
to "program killed by signal 11" on run.dlang.io).
```d
import std.stdio : writeln, writefln;
import std.random : uniform01;
import core.memory : GC;
import core.simd;
void main() {
float8[] a = new float8[128];
float8[] b = new float8[128];
float8[] c = new float8[128];
writeln(&a, " ", &b, " ", &c);
writeln(a.ptr, " ", b.ptr, " ", c.ptr);
writeln("Filling array...");
for (size_t i = 0; i < c.length; ++i) {
// If I understand correctly, lines below assign 8
equal float values to float8 (does not matter in this test?)
a[i] = uniform01();
b[i] = uniform01();
}
writeln("Performing arithmetics...");
for (size_t i = 0; i < c.length; ++i) {
c[i] = a[i] * b[i];
}
writeln("Checking array...");
for (size_t i = 0; i < c.length; i += 8) {
if (c[i].array != (a[i] * b[i]).array) {
writefln("Value in array c is not product (i = %s):
%s != %s + %s", i, c[i], a[i], b[i]);
break;
}
}
}
```
Output:
```
7FFF602EF5A0 7FFF602EF590 7FFF602EF580
7F15CB784010 7F15CB786010 7F15CB788010
Filling array...
Error: /tmp/onlineapp-835ef2 failed with status: -2
message: Segmentation fault (core dumped)
Error: program received signal 2 (Interrupt)
```
This is a long-standing druntime bug: alignment of the type is
not taken into account for GC allocations... Wow.
https://github.com/dlang/dmd/issues/17259
-Johan
- Johan
