When the following program is compiled with GDC 14.1, the assertion fails:

void main() {
    int d = 42;
    bool o = d > d++;
    assert(o == false);
}

(Godbolt: https://d.godbolt.org/z/e63xbb9Td)

The assertion passes when the program is compiled with DMD 2.108.0.

The same bug was recently reported for LDC: https://github.com/ldc-developers/ldc/issues/4651

On Wednesday, 8 May 2024 at 14:26:25 UTC, Paul Backus wrote:

void main() {
    int d = 42;
    bool o = d > d++;
    assert(o == false);
}

I want to say that rewriting d > d++ to d++ < d is a valid optimization.

See also opCmp rewriting a < b into b.opCmp(a)

https://dlang.org/spec/operatoroverloading.html#compare

On Thursday, 9 May 2024 at 18:24:12 UTC, Iain Buclaw wrote:

void main() {
    int d = 42;
    bool o = d > d++;
    assert(o == false);
}

Even when it doesn't swap order, DMD doesn't store the left hand of the expression to a target/temporary when operator overloading is involved.

https://d.godbolt.org/z/jYYr1WMhn

o = d.opCmp(d.opUnary!"++"())

Effectively

arg = d.opUnary!"++"(); // d mutates
o = d.opCmp(arg) > 0;   // true