Sema: Fix comparison with undefined 2

[wrongnull]

Closes #17798
This is my second attempt to close this issue but with behavior test instead of compile-error one. I'm also not quite sure what should I do with this #17900 (comment) so @andrewrk please let me know what was wrong there.

[Vexu]

I don't understand that review comment either.

[andrewrk]

If you look at git blame for this comment, it comes from 6e78c00.

The commit message there says that it was done for a particular desired codegen output. Since you are messing with this code and mentioned not understanding what this comment was talking about, it would be nice if the writeup for this patch demonstrated that this behavior did not regress. In other words, make sure x == true and x == false where x is a boolean are still lowered as a no-op or a not. There is no test coverage for this, so it has to be manually verified.

[wrongnull]

If you look at git blame for this comment, it comes from 6e78c00.

The commit message there says that it was done for a particular desired codegen output. Since you are messing with this code and mentioned not understanding what this comment was talking about, it would be nice if the writeup for this patch demonstrated that this behavior did not regress. In other words, make sure x == true and x == false where x is a boolean are still lowered as a no-op or a not. There is no test coverage for this, so it has to be manually verified.

Just like the following?

wrongnull@DESKTOP-22AKPRT:~/projects/zig/build/stage3/bin$ ./zig version
0.12.0-dev.6066+ead7b6f5f
wrongnull@DESKTOP-22AKPRT:~/projects/zig/build/stage3/bin$ cat test.zig
pub export fn entry() u32 {
    const x = true;
    if (x == true) {return 0;} else {return 1;}
}
wrongnull@DESKTOP-22AKPRT:~/projects/zig/build/stage3/bin$ ./zig build-obj --verbose-air test.zig
# Begin Function AIR: test.entry:
# Total AIR+Liveness bytes: 299B
# AIR Instructions:         15 (135B)
# AIR Extra Data:           15 (60B)
# Liveness tomb_bits:       8B
# Liveness Extra Data:      0 (0B)
# Liveness special table:   0 (0B)
  %0!= save_err_return_trace_index()
  %2!= dbg_block_begin()
  %3!= dbg_stmt(2:5)
  %4!= dbg_var_val(@Air.Inst.Ref.bool_true, "x")
  %5!= dbg_stmt(3:9)
  %7!= dbg_block_begin()
  %9!= dbg_block_begin()
  %10!= dbg_stmt(3:21)
  %12!= dbg_block_end()
  %13!= dbg_block_end()
  %14!= dbg_block_end()
  %11!= ret(<u32, 0>)
# End Function AIR: test.entry```

[Vexu]

x should be runtime known and the Air should not contain a cmp_eq.

[wrongnull]

x should be runtime known and the Air should not contain a cmp_eq.

wrongnull@DESKTOP-22AKPRT:~/projects/zig/build/stage3/bin$ cat test.zig
pub export fn entry() u32 {
    var x = true;
    if (x == true) {return 0;} else {return 1;}
}
wrongnull@DESKTOP-22AKPRT:~/projects/zig/build/stage3/bin$ ./zig build-obj --verbose-air test.zig
# Begin Function AIR: test.entry:
# Total AIR+Liveness bytes: 479B
# AIR Instructions:         27 (243B)
# AIR Extra Data:           27 (108B)
# Liveness tomb_bits:       16B
# Liveness Extra Data:      2 (8B)
# Liveness special table:   1 (8B)
  %0!= save_err_return_trace_index()
  %2!= dbg_block_begin()
  %3!= dbg_stmt(2:5)
  %4 = alloc(*bool)
  %5!= store(%4, @Air.Inst.Ref.bool_true)
  %7!= dbg_var_ptr(%4, "x")
  %8!= dbg_stmt(3:9)
  %10 = load(bool, %4!)
  %26!= dbg_block_end()
  %25!= cond_br(%10!, {
    %11!= dbg_block_begin()
    %13!= dbg_block_begin()
    %14!= dbg_stmt(3:21)
    %16!= dbg_block_end()
    %17!= dbg_block_end()
    %15!= ret(<u32, 0>)
  }, {
    %18!= dbg_block_begin()
    %20!= dbg_block_begin()
    %21!= dbg_stmt(3:38)
    %23!= dbg_block_end()
    %24!= dbg_block_end()
    %22!= ret(<u32, 1>)
  })
# End Function AIR: test.entry

[andrewrk]

I'm sorry, I didn't review this in time, and now it has bitrotted. Furthermore, so many pull requests have stacked up that I can't keep up and I am therefore declaring Pull Request Bankruptcy and closing old PRs that now have conflicts with master branch.

If you want to reroll, you are by all means welcome to revisit this changeset with respect to the current state of master branch, and there's a decent chance your patch will be reviewed the second time around.

Either way, I'm closing this now, otherwise the PR queue will continue to grow indefinitely.

[wrongnull]

I'm sorry, I didn't review this in time, and now it has bitrotted. Furthermore, so many pull requests have stacked up that I can't keep up and I am therefore declaring Pull Request Bankruptcy and closing old PRs that now have conflicts with master branch.

If you want to reroll, you are by all means welcome to revisit this changeset with respect to the current state of master branch, and there's a decent chance your patch will be reviewed the second time around.

Either way, I'm closing this now, otherwise the PR queue will continue to grow indefinitely.

Okay, don't worry. However, I'm very interested in the zig project, so I'll be sure to make changes accordingly to keep it fresh.