[llvm-dev] what is official way to determine if we are running lto 2nd stage?

[Konstantin Vladimirov via llvm-dev]

Hi,

Imagine that your backend has valid asm instruction written like this:

"%x mnem %y, %z"

And user puts it as inline assembler:

__asm__ ("%x mnem %y, %z");

It can not be parsed with current llvm asm parser, because it starts
with % (moreover it has mnemonic in second place)

Say you written pass, that makes it "mnem %x, %y, %z".

Now this guy can be parsed, but can not be encoded by gas. You simply
havent that instruction in you assembler. For LTO it isn't a problem:
you can make arbitrary MCInst from everything that comes into
ParseInstruction. But it is problem for regular scenario where wrong
asm will be printed and then passed to gas.

So I want to apply this on 2nd lto stage where AsmParser is inevitable
and to not apply in non-LTO cases.

---
With best regards, Konstantin

On Mon, Sep 12, 2016 at 10:19 PM, Mehdi Amini <mehdi.amini at apple.com> wrote:
>
>> On Sep 12, 2016, at 11:07 AM, Konstantin Vladimirov <konstantin.vladimirov at gmail.com> wrote:
>>
>> Hi,
>>
>> This is really basic block level pass. It is no difference what is
>> level, problem is the same.
>
> Can you clarify what you mean? If you have a MachineFunction pass, it’ll run in the backend only.
> I don’t understand why you would need to distinguish between LTO or no-LTO here.
>
>>
>> After fixing for asm parser, assembler syntax is no more valid for
>> backend, without processing with asm parser.
>
> My understanding of Inline ASM is that it is supposed to be opaque to the backend till you reach MC.
> So I don’t understand this sentence "no more valid for backend, without processing with asm parser”.
>
> Sorry if my answers don’t make sense to you, I may still be missing a key part of your problem.
>
> —
> Mehdi
>
>
>> May be it will be solution to process inline asm on insn printer level
>> to remove syntax fixes. But just switch it off without lto will make
>> compiler do less job
>>
>> P.S. sorry for dup, maillist CC lost on first sent.
>>
>> ---
>> WIth best regards, Konstantin
>>
>>
>> On Mon, Sep 12, 2016 at 8:52 PM, Mehdi Amini <mehdi.amini at apple.com> wrote:
>>>
>>>> On Sep 12, 2016, at 9:26 AM, Konstantin Vladimirov <konstantin.vladimirov at gmail.com> wrote:
>>>>
>>>> Hi,
>>>>
>>>> In LTO we have AsmParser that process inline assembler instructions to
>>>> MCInst and I want to fix some inline assembler in order to conform its
>>>> rules (do not start with non-identifier and so on) because asm syntax
>>>> of our backend allows some incompatible patterns. In order to do this
>>>> I am adding IR-level target-specific pass. But those fixes shall not
>>>> be applied when there is no AsmParser later to process them. So I want
>>>> to switch this pass off if we are not in 2nd lto stage.
>>>
>>> This is not clear to me: how should this be different for LTO than for a non-LTO compile?
>>>
>>> Also, if you’re only fixing the inline ASM, why doing it as an IR-level pass instead of MachineFunctionPass?
>>>
>>> —
>>> Mehdi
>>>
>>>
>>>>
>>>> I think, I can make target-specific option and make user to supply it
>>>> whenever he wants to run 2nd lto stage, but this is ugly.
>>>>
>>>> Can I somehow ask, say, about whole string of options and then parse
>>>> it to match "lto" from here?
>>>>
>>>> ---
>>>> With best regards, Konstantin
>>>>
>>>> On Mon, Sep 12, 2016 at 6:17 PM, Mehdi Amini <mehdi.amini at apple.com> wrote:
>>>>> Hi,
>>>>>
>>>>>
>>>>>> On Sep 12, 2016, at 1:26 AM, Konstantin Vladimirov via llvm-dev <llvm-dev at lists.llvm.org> wrote:
>>>>>>
>>>>>> Hi,
>>>>>>
>>>>>> I want to enable some target-specific functionality only if current
>>>>>> build is 2nd LTO stage (i.e. optimizer called from plugin). What is
>>>>>> best and recommended way to do it?
>>>>>
>>>>> There is none. We can setup a different optimizer pass pipeline for LTO, but the target specific part (i.e. the backend) isn’t supposed to behave differently.
>>>>>
>>>>> This is an issue in general with LTO where options from the command line (like -fno-builtins, or -fveclib=xxxx) are not correctly propagated to LTO.
>>>>>
>>>>> What kind of behavior do you want to enable exactly?
>>>>>
>>>>> —
>>>>> Mehdi
>>>>>
>>>
>