[Bug d/95174] New: [D] Incorrect compiled functions involving const fixed size arrays

[witold.baryluk+gcc at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95174

            Bug ID: 95174
           Summary: [D] Incorrect compiled functions involving const fixed
                    size arrays
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: d
          Assignee: ibuclaw at gdcproject dot org
          Reporter: witold.baryluk+gcc at gmail dot com
  Target Milestone: ---

https://explore.dgnu.org/z/LppySp


```
void f(immutable(float[64]) x, float[64] o) {
   o[] = x[] * 2.0f;
}
```

and

```
void f(immutable(float[64]) x, float[64] o) {
    foreach (i; 0 .. 64) {
        o[i] = x[i] * 2.0f;
    }
}
```

and

```
void f(immutable(float[64]) x, float[64] o) {
    o[1] = x[5] + x[7];
}

```

Is incorrectly compiled to 'nop; ret'


It appears DMD (v2.092) also essentially do the same, and do not perform any
computations in the function.

LDC2 (1.20.1, based on DMD v2.090.1) does generate correct code in some cases
(fully unrolled and fully vectorized in this specific case), but in some other
also do nothing and simply does 'ret' in the function.



As a bonus:

```
void fffff(immutable(float[4]) x, float[4] o) {
   o[2] = x[1] + x[3];
}

import std.stdio : writeln;

void main() {
  immutable(float[4]) k = [7.0f, 5.3f, 1.2f, 3.2f];
  float[4] o;
  fffff(k, o);
  writeln(o);
}

```

prints '[nan, nan, nan, nan]', but it should: '[nan, nan, 8.5, nan]'.


I got the same results using my local gdc version 10.1.0 on amd64.