[llvm-dev] New Pass Manager '<' '>' syntax

[Cameron McInally via llvm-dev]

> When printing a command that a user can use, each argument is typically quoted/escaped.

That's fair enough for options that contain !(alphanumeric / select
other) characters. But, the quoted/escaped '<' and '>' choice is still
unusual. Case in point, if someone proposed a "-fno unroll loops"
option, that needs to be quoted/escaped, I would expect pushback there
too.

On Thu, Nov 11, 2021 at 4:08 PM Arthur Eubanks <aeubanks at google.com> wrote:
>
> 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