llvm dev - Nov 2021 - New Pass Manager '<' '>' syntax

Hey llvm-dev,

The new Pass Manager's "-passes=default<Ox>" syntax is a
little wonky.
It was unfortunate that "<" and ">" were chosen, since
those are the
Unix I/O redirection operators.

Let's take the case of a simple driver:

#include <stddef.h>
#include <unistd.h>
#include <string.h>
#include <stdio.h>

int main(int argc, char *argv[]) {
  char* cmd = "opt";
  char* arr[] = {"-passes=default<O2>", "-S",
"test.ll", NULL};

  if (argc == 1)
    execv(cmd, arr);
  else {
    if (strcmp(argv[1], "-###") == 0) {
        printf("%s ", cmd);
      for(int i =0 ; arr[i] != NULL; i++)
        printf("%s ", arr[i]);
      printf("\n");
    }
  }
  return 0;
}

So there's two modes there: execute the opt subcommand; or dump the
subcommand in a dryrun. Typically, we'd want to be able to
copy-and-paste the output of the dryrun to the command line.

$ ./driver -###
opt -passes=default<O2> -S test.ll
$ opt -passes=default<O2> -S test.ll
-bash: O2: No such file or directory

But in this case, the new -passes=default<O2> option makes that
awkward since we'd need to escape the '<' and '>'
symbols, so that the
shell doesn't interpret them as I/O redirectors.

Unfortunately, patching this up in our driver is clunky. So I'm
reaching out to the list to see if there's an appetite for a better
way to express this option.

Thanks,
Cameron

When printing a command that a user can use, each argument is typically
quoted/escaped. This is true of almost every tool I've used that prints out
a command to copy paste and seems like the proper solution. I don't think
it's reasonable to assume that without any work, raw arguments are shell
copy pastable.
For example, a file name with a space would already not work with your
proposed driver -###.

On Thu, Nov 11, 2021 at 12:42 PM Cameron McInally via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Hey llvm-dev,
>
> The new Pass Manager's "-passes=default<Ox>" syntax is
a little wonky.
> It was unfortunate that "<" and ">" were chosen,
since those are the
> Unix I/O redirection operators.
>
> Let's take the case of a simple driver:
>
> #include <stddef.h>
> #include <unistd.h>
> #include <string.h>
> #include <stdio.h>
>
> int main(int argc, char *argv[]) {
>   char* cmd = "opt";
>   char* arr[] = {"-passes=default<O2>", "-S",
"test.ll", NULL};
>
>   if (argc == 1)
>     execv(cmd, arr);
>   else {
>     if (strcmp(argv[1], "-###") == 0) {
>         printf("%s ", cmd);
>       for(int i =0 ; arr[i] != NULL; i++)
>         printf("%s ", arr[i]);
>       printf("\n");
>     }
>   }
>   return 0;
> }
>
> So there's two modes there: execute the opt subcommand; or dump the
> subcommand in a dryrun. Typically, we'd want to be able to
> copy-and-paste the output of the dryrun to the command line.
>
> $ ./driver -###
> opt -passes=default<O2> -S test.ll
> $ opt -passes=default<O2> -S test.ll
> -bash: O2: No such file or directory
>
> But in this case, the new -passes=default<O2> option makes that
> awkward since we'd need to escape the '<' and '>'
symbols, so that the
> shell doesn't interpret them as I/O redirectors.
>
> Unfortunately, patching this up in our driver is clunky. So I'm
> reaching out to the list to see if there's an appetite for a better
> way to express this option.
>
> Thanks,
> Cameron
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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