Bug in optimization of zero right shift

[dlangBugzillaToGithub]

Yui Hosaka reported this on 2019-08-13T18:44:58Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=20128

Description

The following code produces weird results:

----
import std.stdio;

void main() {
  auto a = new long[4];
  foreach (i; 0 .. 4) {
    a[i] = 1 << i;
  }
  writeln(a);

  auto b = new long[4];
  foreach (i; 0 .. 4) {
    b[i] = (((1 >> i) & 1) ? -1 : +1) * a[i];
  }
  writeln(b);
}
----

(https://ideone.com/2NzVaA)

Its outputs are:
[1, 2, 4, 8]
[4294967295, 2, 4, 8]

while b[0] is supposed to be -1.

This happens only with -m64 and -O options.