On Monday, 13 March 2023 at 15:23:25 UTC, user1234 wrote:
[snip]
[1]
https://theunixzoo.co.uk/blog/2021-10-14-preventing-optimisations.html
that's illegal code. You mix GCC/LLVM syntax with D asm block
and the front-end wont recognize that.
LDC recognizes a syntax similar to what is described in your
link, see
https://wiki.dlang.org/LDC_inline_assembly_expressions. GDC has
it too (since that the syntax invented by GCC in first place)
but I cant find the documentation ATM.
Thanks, that helps. Below seems to be working...(with LDC and -O)
when I include the DoNotOptimize, it takes around 300-500us, but
when I comment it out, then it takes about 5us. It would still
take some work to figure out how to get it to work with DMD.
```d
void DoNotOptimize(T)(T* ptr)
{
import ldc.llvmasm;
import core.volatile: volatileLoad;
T value = volatileLoad(ptr);
__asm("", "*mr,~{memory}", &value, );
}
void main() {
import std.algorithm.iteration: sum;
import std.array: uninitializedArray;
import std.datetime.stopwatch;
import std.random: uniform;
import std.stdio: writeln;
auto testData = uninitializedArray!(long[])(600_000);
foreach(ref el; testData) el = uniform(0, 10);
ulong seed = 0;
ulong output = 0;
StopWatch sw;
sw.start();
DoNotOptimize(&seed);
output = testData.sum(seed);
DoNotOptimize(&output);
sw.stop();
writeln("time: ", sw.peek);
}
```
