similar to: [LLVMdev] [RFC] Attributes on Values

LLVM's Attribute APIs need an overhaul. Current problems ================ First, testing for an attribute on an Argument is slow. llvm::AttributeSet::getAttributes(int) consumed 2% of cycles while optimizing llc during LTO. Our mid-level optimizations are constantly asking if a given argument has some attribute (nonnull, dereferencable, etc), and this is currently linear in the size of the

Using the New Attributes Classes Attributes in LLVM have changed in some fundamental ways. It was necessary to do this to support expanding the attributes to encompass more than a handful of attributes --- e.g. command line options. The old way of handling attributes consisted of representing them as a bit mask of values. This bit mask was stored in a "list" structure that was reference

On 02/19, Juneyoung Lee via llvm-dev wrote: > Hello, > > > Would it be correct to resolve this by saying that dereferenceable(N) > > *implies* not_poison? This would be helpful as a clarification of how > > it all fits together. > > Yes, I think it makes sense. I don't we should do that. Take the `gep inbounds` example: char* foo(char *arg) { return `gep

----- Original Message ----- > From: "Philip Reames" <listmail at philipreames.com> > To: "LLVM Developers Mailing List" <llvmdev at cs.uiuc.edu> > Sent: Friday, February 27, 2015 5:34:36 PM > Subject: Re: [LLVMdev] RFC: PerfGuide for frontend authors > > The first version of this document is now live: >

On Wed, Feb 19, 2020 at 3:51 AM Juneyoung Lee via llvm-dev <llvm-dev at lists.llvm.org> wrote: > I think not_poison (Johannes's used keyword) makes sense. We can simulate the original UB semantics by simply attaching it, as explained. > For the attributes other than nonnull, we may need more discussion; align attribute seems to be okay with defining it as poison, dereferenceable

Two thoughts: 1. I think that we should aim for regularity, to the extent possible, and so we should treat nonnull, align, etc. similarly w.r.t. to whether they produce poison or UB. 2. I was thinking about the following last night, and it clarified for me why having an not_poison attribute makes sense and seems useful, and how poison/UB might affect things on a function-call boundary itself.

I'd like to propose that we add an attribute which expresses the notion that the specified value is /either/ null or dereferenceable up to a fixed size. (Note the xor.) Our current dereferenceable(n) attribute doesn't quite fit the bill, it implies that the pointer is non-null. Similarly, our nonnull attribute says nothing about dereferenceability. There are two syntax proposals

Hey list, I've recently done the first test run of bumping our Burst compiler from LLVM 10 -> 11 now that the branch has been cut, and have noticed an apparent loop vectorization codegen regression for X86 with AVX or AVX2 enabled. The following IR example is vectorized to 4 wide with LLVM 11 and trunk whereas in LLVM 10 it (correctly as per what we want) vectorized it 8 wide matching the

Hi all, Sorry for the inconvenient about the previous post. The files were not attached. So I put them here again. I am a newbie in LLVM and I am trying to replace the function like: old function || new function ============================== ========= int haha(int a) { int haha(int a, char* ID) { ===> }

I think calling the attribute "used" is confusing. I'd suggest the following: "not_poison": If an argument is marked not_poison, and the argument is poison at runtime, the call is instant UB. Whether an argument is poison is checked after the rules for other attributes like "nonnull" and "align" are applied. This makes it clear that the IR semantics

Hello all, LangRef says it is undefined behavior to pass null to a nonnull argument (`call f(nonnull null);`), but the semantics is too strong for a few existing optimizations. To support these, we can relax the semantics so `f(nonnull null)` is equivalent to `f(poison)`, but (A) it again blocks another set of optimizations, and (B) this makes the semantics of nonnull deviate from other

Hi Johannes, >> Not sure the semantics of "used" you propose is sufficient. AFAIU the >> proposal, "used" could only be used in cases where the function will >> always trigger UB if poison is passed as argument. The semantics of >> attributes is usually the other way around, since function calls need >> to have UB as strong as the worst

HI, When compiling the open-source software cryptopp (https://www.cryptopp.com/#download <https://www.cryptopp.com/#download>) version 5.6.4 I found a strange issue with the IR generated. The issue only appears when compiling with -O2 optimisation in the integer.cpp file (the function is _ZN8CryptoPPrsERNSt3__113basic_istreamIcNS0_11char_traitsIcEEEERNS_7IntegerE ->

Tried a bunch of them there (x86-64, haswell, znver2) and they all defaulted to 4-wide - haswell additionally caused some extra loop unrolling but still with 8-wide pows. Cheers, -Neil. On Thu, Jul 16, 2020 at 2:39 PM Roman Lebedev <lebedev.ri at gmail.com> wrote: > Did you specify the target CPU the code should be optimized for? > For clang that is -march=native/znver2/... /

Hello, What intrinsics "@llvm.lifetime.start/@llvm.lifetime.end" really do? As per my knowledge, they define the live ranges of variables. In the following code section, they seem redundant. However, when I remove them, the behavior of the code becomes non-deterministic. The live ranges of the variables defined by them are never used in the code. Thanks, --------------- %37 = bitcast

> On Feb 27, 2015, at 3:58 PM, Hal Finkel <hfinkel at anl.gov> wrote: > > ----- Original Message ----- >> From: "Philip Reames" <listmail at philipreames.com> >> To: "LLVM Developers Mailing List" <llvmdev at cs.uiuc.edu> >> Sent: Friday, February 27, 2015 5:34:36 PM >> Subject: Re: [LLVMdev] RFC: PerfGuide for frontend

Hi all, I would like to propose a new way clang would decorate vtable loads in order to handle devirtualization better. I've added *llvm-dev* also, because this can start a discussion about changing invariant.group to just invariant. PDF version of this RFC can be found here: https://drive.google.com/file/d/0B72TmzNsY6Z8ZmpOUnB5dDZfSFU/view?usp=sharing Background: Initial old design:

Not sure the semantics of "used" you propose is sufficient. AFAIU the proposal, "used" could only be used in cases where the function will always trigger UB if poison is passed as argument. The semantics of attributes is usually the other way around, since function calls need to have UB as strong as the worst behavior of the function. If a function may for some reason trigger

While improving ADCE, i notice that for declare i32 @strlen(i8*) readnone define i32 @test() { ; invoke of pure function should not be deleted! invoke i32 @strlen( i8* null ) readnone to label %Cont unwind label %Other ; <i32>:1 [#uses=0] Cont: ; preds = %0 ret i32 0 Other: ; preds = %0 %exn = landingpad {i8*, i32} personality i32 (...)* @__gxx_personality_v0

=== PROBLEM === (See this bug https://llvm.org/bugs/show_bug.cgi?id=26445) IR contains code for loading a float from float * and storing it to a float * address. After canonicalization of load in InstCombine [1], new bitcasts are added to the IR (see bottom of the email for code samples). This prevents select speculation in SROA to work. Also after SROA we have bitcasts from int32 to float.