Clarrification for bad codegen on postfix operators

[dlangBugzillaToGithub]

Richard (Rikki) Andrew Cattermole reported this on 2024-05-17T14:59:01Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=24554

Description

Johan Engelen asked me on the ldc bug ticket to create a ticket to find out what the specification means.

All three compilers have differing behavior.

DMD: https://github.com/ldc-developers/ldc/issues/4651

GDC: https://forum.dlang.org/post/[email protected]

ldc fe 2.107 as per run.dlang.org

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

```
define i32 @_Dmain({ i64, ptr } %unnamed) #0 {
  %d = alloca i32, align 4                        ; [#uses = 4, size/byte = 4]
  %o = alloca i8, align 1                         ; [#uses = 1, size/byte = 1]
  store i32 42, ptr %d, align 4
  %1 = load i32, ptr %d, align 4                  ; [#uses = 2]
  %2 = add i32 %1, 1                              ; [#uses = 1]
  store i32 %2, ptr %d, align 4
  %3 = load i32, ptr %d, align 4                  ; [#uses = 1]
  %4 = icmp sgt i32 %3, %1                        ; [#uses = 1]
  %5 = zext i1 %4 to i8                           ; [#uses = 1]
  store i8 %5, ptr %o, align 1
  ret i32 0
}
```

Note; the icmp is after the add, which it shouldn't be.

Source: https://twitter.com/marcos_don/status/1787629240550150361