Looks good. Can you add a new test to cover this? Something like:

const myP = @intToPtr(*u16, 0x2300);

test "mutate through ptr initialized with constant intToPtr value" {
  myP.* = myP.* | 10;
}

Probably a good place for it would be test/cases/inttoptr.zig.

Oops, good point. What we can do is put the logic in an if statement that will always be false, but make the compiler unable to determine the value at compile-time, so that it must analyze the branch. One way to do this, for example, is to pass false as a bool parameter, and then do an if on that bool.

This may be another good candidate for LLVM IR tests, when I get around to introducing that kind of test.

Like so?

test "mutate through ptr initialized with constant intToPtr value" {
    forceCompilerAnalyzeBranchHardCodedPtrDereference(false);
}

fn forceCompilerAnalyzeBranchHardCodedPtrDereference(x: bool) void {
    const hardCodedP = @intToPtr(*volatile u8, 0xdeadbeef);
    if (x) {
        hardCodedP.* = hardCodedP.* | 10;
    } else {
        return;
    }
}

It does pass.

Looks good to me.

It used to do that implicitly, but not anymore. There are some problems to solve when trying to reinstate that behavior. The issue to track is #425. If we ever changed this behavior, a lot of tests would have to be modified, which rely on this behavior. So safe to assume that this new test case would be part of that audit.

Do I need to re-trigger the build before acceptance?

It's building. Should be done in about an hour. But enough of the tests pass that I'm confident it will finish successfully, so I'll go ahead and merge. Thanks again for the fix!