llvm dev - Mar 2019 - Add Bitwidth Attribute in Clang without Modification in Source Code of Clang

Dear all,

    I write a new LoopPass which wants to use passes including
LoopInfoWrapperPass, ScalarEvolutionWrapperPass and LoopAccessLegacyAnalysis.
    Therefore, I implement the following code based on LLVM 9.0.0:

====================================================================bool
LoopInformationCollect::runOnLoop(Loop *L, LPPassManager &)
{

    auto &SE = getAnalysis<ScalarEvolutionWrapperPass>().getSE();
    auto &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
    // auto *LAA = &getAnalysis<LoopAccessLegacyAnalysis>();
    if (Loop_id.find(L)==Loop_id.end()) // traverse instructions in the block
assign instruction ID
    {
        Loop_id[L] = ++Loop_Counter;
    }
    // *Loop_out << "---------------Loop
report----------------\n";
    // *Loop_out << LAA->getInfo(L).getReport();
    return false;
}

char LoopInformationCollect::ID = 0;

void LoopInformationCollect::getAnalysisUsage(AnalysisUsage &AU) const {
    AU.addRequired<LoopInfoWrapperPass>();
    AU.addRequired<ScalarEvolutionWrapperPass>();
    AU.addRequired<LoopAccessLegacyAnalysis>();
    AU.setPreservesAll();
}
====================================================================
   I can make the project with GNU make successfully but get the error
"Pass 'Unnamed pass: implement Pass::getPassName()' is not
initialized." during runtime. When I remove the line
"AU.addRequired<LoopAccessLegacyAnalysis>();" and make the
project again, I run the program successfully.

   Detailed error report is shown below:

---------------------------------------------------------------------------------------------------------
Pass 'Unnamed pass: implement Pass::getPassName()' is not initialized.
Verify if there is a pass dependency cycle.
Required Passes:
        Natural Loop Information
        Scalar Evolution Analysis
---------------------------------------------------------------------------------------------------------

   Please note that I am not using "opt" in the terminal to run the
passes but utilize PassManager in a main() function. It seems that the problem
is caused by "LoopAccessLegacyAnalysis", since I have not faced this
problem with other passes. I am wondering how I can fix this situation.
   Thanks a lot for your time and suggestions!

Best regards,
------------------------------------------
Tingyuan LIANG
MPhil Student
Department of Electronic and Computer Engineering
The Hong Kong University of Science and Technology
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Hi,

you will have to call
initializeLoopAccessLegacyAnalysisPass(*PassRegistry::getPassRegistry())
before you can use it as a pass dependency. This is usually done by a
sequence of

INITIALIZE_PASS_BEGIN(YourPass, "your_pass", "Your Pass
Name", false, false)
INITIALIZE_PASS_DEPENDENCY(LoopAccessLegacyAnalysis)
INITIALIZE_PASS_END(YourPass, "your_pass", "Your Pass Name",
false, false)

which also creates an initializer for your pass:
initializeYourPassPass which you should call in some way in your
application.

Michael


Am Fr., 1. Feb. 2019 um 12:58 Uhr schrieb Tingyuan LIANG via llvm-dev
<llvm-dev at lists.llvm.org>:
>
> Dear all,
>
>     I write a new LoopPass which wants to use passes including
LoopInfoWrapperPass, ScalarEvolutionWrapperPass and LoopAccessLegacyAnalysis.
>     Therefore, I implement the following code based on LLVM 9.0.0:
>
> ====================================================================>
bool LoopInformationCollect::runOnLoop(Loop *L, LPPassManager &)
> {
>
>     auto &SE = getAnalysis<ScalarEvolutionWrapperPass>().getSE();
>     auto &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
>     // auto *LAA = &getAnalysis<LoopAccessLegacyAnalysis>();
>     if (Loop_id.find(L)==Loop_id.end()) // traverse instructions in the
block assign instruction ID
>     {
>         Loop_id[L] = ++Loop_Counter;
>     }
>     // *Loop_out << "---------------Loop
report----------------\n";
>     // *Loop_out << LAA->getInfo(L).getReport();
>     return false;
> }
>
> char LoopInformationCollect::ID = 0;
>
> void LoopInformationCollect::getAnalysisUsage(AnalysisUsage &AU) const
{
>     AU.addRequired<LoopInfoWrapperPass>();
>     AU.addRequired<ScalarEvolutionWrapperPass>();
>     AU.addRequired<LoopAccessLegacyAnalysis>();
>     AU.setPreservesAll();
> }
> ====================================================================>
>    I can make the project with GNU make successfully but get the error
"Pass 'Unnamed pass: implement Pass::getPassName()' is not
initialized." during runtime. When I remove the line
"AU.addRequired<LoopAccessLegacyAnalysis>();" and make the
project again, I run the program successfully.
>
>    Detailed error report is shown below:
>
>
---------------------------------------------------------------------------------------------------------
> Pass 'Unnamed pass: implement Pass::getPassName()' is not
initialized.
> Verify if there is a pass dependency cycle.
> Required Passes:
>         Natural Loop Information
>         Scalar Evolution Analysis
>
---------------------------------------------------------------------------------------------------------
>
>    Please note that I am not using "opt" in the terminal to run
the passes but utilize PassManager in a main() function. It seems that the
problem is caused by "LoopAccessLegacyAnalysis", since I have not
faced this problem with other passes. I am wondering how I can fix this
situation.
>    Thanks a lot for your time and suggestions!
>
> Best regards,
> ------------------------------------------
> Tingyuan LIANG
> MPhil Student
> Department of Electronic and Computer Engineering
> The Hong Kong University of Science and Technology
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

Dear Michael,

    Thanks a lot for your suggestion but I not sure whether it is caused by this
initialization because for example, I do not do such initialization for
LoopInfoWrapperPass in my code but it works fine.

    I tried your solution for the pass but got the following compilation error
----> namespace "llvm" has no member
"initializeLoopInformationCollectPass".

    Such error is raised from the macro define: INITIALIZE_PASS_END. Does it
mean I need to specially define such function in the LLVM namespace?

    Thanks again for your time and patience!

Best regards,
------------------------------------------
Tingyuan LIANG
MPhil Student
Department of Electronic and Computer Engineering
The Hong Kong University of Science and Technology
________________________________
From: Michael Kruse <llvmdev at meinersbur.de>
Sent: Saturday, February 2, 2019 6:10 AM
To: Tingyuan LIANG
Cc: llvm-dev at lists.llvm.org
Subject: Re: [llvm-dev] Confusing ERROR with LoopAccessLegacyAnalysis: Pass
'Unnamed pass: implement Pass::getPassName()' is not initialized.

Hi,

you will have to call
initializeLoopAccessLegacyAnalysisPass(*PassRegistry::getPassRegistry())
before you can use it as a pass dependency. This is usually done by a
sequence of

INITIALIZE_PASS_BEGIN(YourPass, "your_pass", "Your Pass
Name", false, false)
INITIALIZE_PASS_DEPENDENCY(LoopAccessLegacyAnalysis)
INITIALIZE_PASS_END(YourPass, "your_pass", "Your Pass Name",
false, false)

which also creates an initializer for your pass:
initializeYourPassPass which you should call in some way in your
application.

Michael


Am Fr., 1. Feb. 2019 um 12:58 Uhr schrieb Tingyuan LIANG via llvm-dev
<llvm-dev at lists.llvm.org>:
>
> Dear all,
>
>     I write a new LoopPass which wants to use passes including
LoopInfoWrapperPass, ScalarEvolutionWrapperPass and LoopAccessLegacyAnalysis.
>     Therefore, I implement the following code based on LLVM 9.0.0:
>
> ====================================================================>
bool LoopInformationCollect::runOnLoop(Loop *L, LPPassManager &)
> {
>
>     auto &SE = getAnalysis<ScalarEvolutionWrapperPass>().getSE();
>     auto &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
>     // auto *LAA = &getAnalysis<LoopAccessLegacyAnalysis>();
>     if (Loop_id.find(L)==Loop_id.end()) // traverse instructions in the
block assign instruction ID
>     {
>         Loop_id[L] = ++Loop_Counter;
>     }
>     // *Loop_out << "---------------Loop
report----------------\n";
>     // *Loop_out << LAA->getInfo(L).getReport();
>     return false;
> }
>
> char LoopInformationCollect::ID = 0;
>
> void LoopInformationCollect::getAnalysisUsage(AnalysisUsage &AU) const
{
>     AU.addRequired<LoopInfoWrapperPass>();
>     AU.addRequired<ScalarEvolutionWrapperPass>();
>     AU.addRequired<LoopAccessLegacyAnalysis>();
>     AU.setPreservesAll();
> }
> ====================================================================>
>    I can make the project with GNU make successfully but get the error
"Pass 'Unnamed pass: implement Pass::getPassName()' is not
initialized." during runtime. When I remove the line
"AU.addRequired<LoopAccessLegacyAnalysis>();" and make the
project again, I run the program successfully.
>
>    Detailed error report is shown below:
>
>
---------------------------------------------------------------------------------------------------------
> Pass 'Unnamed pass: implement Pass::getPassName()' is not
initialized.
> Verify if there is a pass dependency cycle.
> Required Passes:
>         Natural Loop Information
>         Scalar Evolution Analysis
>
---------------------------------------------------------------------------------------------------------
>
>    Please note that I am not using "opt" in the terminal to run
the passes but utilize PassManager in a main() function. It seems that the
problem is caused by "LoopAccessLegacyAnalysis", since I have not
faced this problem with other passes. I am wondering how I can fix this
situation.
>    Thanks a lot for your time and suggestions!
>
> Best regards,
> ------------------------------------------
> Tingyuan LIANG
> MPhil Student
> Department of Electronic and Computer Engineering
> The Hong Kong University of Science and Technology
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
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Hi all,

    I am handling some arbitrary precision integers (e.g. 13-bit) in the source
code with Clang. Temporary, I declare them as structs like:

              struct APINT13 VarA;

    and during parsing the AST and generating IR, I transform the type of these
variables into arbitrary precision integers.
    I read some other documentations and find that adding attributes for
variables could be a nicer way to handle arbitrary precision integer.
    However, as default, there is no such attribute as "bitwidth" in
Clang. I found the following link and get some hints but the instructions listed
in the website require me to modify the source code of Clang
("Attr.td", "include/clang/Sema/ParsedAttr.h" and
"utils/TableGen/ClangAttrEmitter.cpp").

    http://clang.llvm.org/docs/InternalsManual.html#how-to-add-an-attribute

    I just wonder whether there is any way to add attributes like plugins
without touching the source code of Clang, because to rebuild Clang could be
time-consuming. As I know, LLVM passes can work as plugins and I guess there
could be the similar way to handle attribute addition with Clang.
    Thanks in advance for your time and suggestion! \^_^/

Best regards,
------------------------------------------
Tingyuan LIANG
MPhil Student
Department of Electronic and Computer Engineering
The Hong Kong University of Science and Technology
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I've actually got an implementation of this as an arbitrary precision
integer extension that I've written up an RFC for (but not submitted). 
Below is my copy/pasted RFC (again, not reviewed, but I DO have an
implementation of it that I need to prepare for review).  I suspect my
implementation will do what you need out of it.  Its actually more significant
than just adding a normal attribute.




Introduction
As we all know, LLVM-IR supports arbitrary precision integers via the iN syntax.
Integers that aren't powers-of-two aren't particularly
interesting/useful on most hardware however, so this functionality isn't
typically used, and in fact, Clang does not have such support.  However, certain
architectures DO exist where the ability to express these values (and do math
without promotion to full integers) is valuable from a performance perspective,
since these values can be expressed more efficiently in hardware.

I've developed a solution to expose these types in clang, and am proposing
to contribute it back to the Clang community if it is sufficiently acceptable to
the group.  As rebasing/refactoring for the open-source version of clang is a
significant effort, I'd like to get feedback on the concept and approach
before putting in this effort.

Syntax
The syntax I'd chosen for this was as a Typedef Attribute.  This permits the
consumer to define various ways to expose this functionality in their code. 
Additionally, we've limited it to int/unsigned typedefs only for
simplicity's sake. The code looks something like:

// Typical way to expose this in C:
typedef int __attribute__((__ap_int(3))) ap_int3;
typedef unsigned __attribute__((__ap_int(3))) ap_uint3;

// Better way to expose it in modern C++:
template<unsigned bits> using ap_int = int
__attribute__((__ap_int(bits)));
template<unsigned bits> using ap_uint = unsigned
__attribute__((__ap_int(bits)));

For our usages, we just wrapped these in a type that would better express the
further configurable semantics, but I suspect these are useful in their own
right.

Conversions/Promotions
We consider conversions to/from integers integral promotions that follow normal
conversion rules, and bool conversions are also supported (just like integers). 
AP-Int math is done at the size of the largest operand in order to be consistent
with C rules as best as possible.  Conversions to/from integers and literals
happen consistently with the other integer types.

Size/Align
One important consideration that was made is how size/alignment is expressed in
the language.  Sizeof, for example works exclusively on bytes, so an
ap_int<13> couldn't be directly expressed.  Alignments are required to
be a power-of-two, otherwise they are not expressable on some hardware.  In
implementation, we chose to use the next largest alignment (up to 64 bits). 
Additionally, for the sake of the standard library (and common array patterns),
we were required to make sizeof also round up to the next power of two.  This is
most consistent with what a majority of LLVM backends will do (for example, an
ap_int<24> will be expressed as a int-32 on most platforms), and was
required to make common array patterns work.  Unfortuantely, this results in
arrays on these platforms having 'padding' bits, but there isn't
really a way around that.

So, is this something that the clang community is interested in?  I'll of
course expect extensive review through phabricator once it is ready, but I'd
like to gauge interest (as well as determine if there is any "over my dead
body" comments) before putting in the significant additional effort.



From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] On Behalf Of Tingyuan
LIANG via llvm-dev
Sent: Sunday, March 3, 2019 4:48 AM
To: llvm-dev at lists.llvm.org
Subject: [llvm-dev] Add Bitwidth Attribute in Clang without Modification in
Source Code of Clang

Hi all,

    I am handling some arbitrary precision integers (e.g. 13-bit) in the source
code with Clang. Temporary, I declare them as structs like:

              struct APINT13 VarA;

    and during parsing the AST and generating IR, I transform the type of these
variables into arbitrary precision integers.
    I read some other documentations and find that adding attributes for
variables could be a nicer way to handle arbitrary precision integer.
    However, as default, there is no such attribute as "bitwidth" in
Clang. I found the following link and get some hints but the instructions listed
in the website require me to modify the source code of Clang
("Attr.td", "include/clang/Sema/ParsedAttr.h" and
"utils/TableGen/ClangAttrEmitter.cpp").

    http://clang.llvm.org/docs/InternalsManual.html#how-to-add-an-attribute

    I just wonder whether there is any way to add attributes like plugins
without touching the source code of Clang, because to rebuild Clang could be
time-consuming. As I know, LLVM passes can work as plugins and I guess there
could be the similar way to handle attribute addition with Clang.
    Thanks in advance for your time and suggestion! \^_^/

Best regards,
------------------------------------------
Tingyuan LIANG
MPhil Student
Department of Electronic and Computer Engineering
The Hong Kong University of Science and Technology
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