similar to: Undef/poison semantics

Hi, Lately we have come to realize how undef makes our life complicated.. Therefore in this email we propose to change the behavior of a few instruction to yield poison instead of undef in error cases. This follows the suggestion of Eli in https://reviews.llvm.org/D33654. Why is undef so bad? - I believe it's not possible to make newgvn correct with undef. See for example the discussion

Hello. I've got a dataset that may have outliers in both x and y. While I am not at all familiar with robust regression, it looked like the function lmrob in package robustbase should handle this situation. When I try to use it, I get: Too many singular resamples Aborting fast_s_w_mem() Looking into it further, it appears that for an indicator variable in one of my interaction terms, 98%

Hi, Let me give you my view of the status: The proposal you mentioned was, I believe, well understood and accepted. Except for one bit, which was that it requires correct typing of load/store operations. That is, if you load an i32, it means you are loading a single 32-bit integer, not two 16-bit integers or something else. This is a valid concern because currently nor LLVM nor clang

Hi, Back in 2016 an RFC titled "Killing Undef and Spreading Poison" [1] was posted on this mailing list, which generated a lot of discussion between different people. Later in 2017, a paper titled "Taming Undefined Behavior in LLVM" [2] was published, detailing the various concerns introduced in the RFC. There is also a patch proposal with an initial implementation

Dear LLVMers, This email is intended for those interested in path-sensitive analysis, integer overflow analysis, static analysis, and (perhaps) loop invariant computation. Traditionally, such analyses have been considered too expensive to be practical, and were mostly an academic curiosity. The core of the problem is the lack of adequate automated decision procedures which could quickly

IMO super optimizer would yield less benefits on LLVM compared to other compilers. If you check the patch of the instcombine pass, you'll find out people keep dragging "correct" optimization out, not because the optimization violates the semantic of LLVM IR, but it will generate wrong code sequences when lowering to machine code. An example: %3 = fcmp %1, %2 %6 = fcmp %4, %5 %7 =

There are probably many mistakes with this code. I am used to coding in C with a debugger, so I am very new to coding in R without one and different syntax. My code in the upper left panel of R Studio isz<-c(3,1,4,5,2,1,0,3,5,8)zlength(z)y<-c(0,0,0,0,0,0,0,0,0,0)ylength(y)zdiff = diff(z)zdiffn<-length(zdiff)nx<-zdifff<-function(x) { for (k in 1:n){

Hi, I know there's been some talk about bignums already, this is similar to it, but not exactly the same. I'm currently using LLVM for my master thesis. The goal is to make a compiler for zero-knowledge proofs of knowledge protocols. This compiler should target embedded devices. There's a language called the protocol implementation language in which these protocols should be

> Only freezing it will > replace it with something concrete such that if x is poison then > freeze(x) == freeze(x), etc. Nit: it's not true that freeze(x) == freeze(x) in the current proposal. Each freeze can choose its own value. John

> On 10/18/2016 3:12 PM, Sanjoy Das wrote: >> But in the new proposal, in: >> >> %x = freeze(poison) >> %y = xor %x, %x >> >> that is no longer allowed (%y _has_ to be 0) -- all uses of %x will see >> some garbage, but fixed bit pattern. > > What about this: > %x = phi poison, poison (I'm simplifying the syntax here) > Can this

John, Here’s what I’m getting at “Poison” is an attribute of a “value”, not a “value” itself. “Poison” is an analysis result, and we should think about implementing it as such, just like we do constant and range analysis. Turning “poison” into a “value” means all “values” now have in addition to a bit pattern an extra attribute (IE a tag). Peter Lawrence.

Hi Zhongxing, On 4/8/07, Zhongxing Xu <xuzhongxing at gmail.com> wrote: > I think the real difficult thing in path sensitive program analysis (or > symbolic execution) is not the lack of decision procedures, but the > translation of arbitrary pointer operations and library function calls in > C/C++ program into the mathematics supported by the automated theorem > prover. >

Hi, The paper is "A Case for an SC-Preserving Compiler" from PLDI 2011. What I did is following their "naive SC preserving compilation", that restricts the compiler to do any reordering for potentially shared load/store instructions. The paper says the resulting code running on x86 machine (SC-preserving binary run on non-SC hardware) will get 22% slowdown comparing with a

> I don't think your example is actually problematic. The original program > before your transformation *executed* undefined behavior in the form of '%x > = add nuw i32 %m, %n' with "%m = %n = 2^32-1 (a.k.a INT_MAX)". If I I was trying to show why the rule "signed overflow is undefined behavior" is problematic w.r.t. hoisting arithmetic by repeating an

On Wed, Jan 28, 2015 at 8:53 PM, Philip Reames <listmail at philipreames.com> wrote: > On 01/28/2015 07:02 AM, Sean Silva wrote: > > Could you maybe provide an example where replacing `%always_poison` with > `undef` will change the meaning? At least for me, the thing that I'm most > unclear about is how poison differs from undef. > > I will second this request for

Hello! With this email we release an extension to OpenSSH that was initially developed as project for our studies at the Univerity of Applied Sciences in Hagenberg. First we would like to describe the purpose of using Zero-Knowledge (ZK) for user authentication. Traditional authentication methods like challenge-response with passwords or public keys leak information about the credentials of

Dear all, I am trying to reproduce the "Percent May Alias" result described in PLDI 07's paper "Making Context-Sensitive Points-to Analysis with Heap Cloning Practical For The Real World" (http://llvm.org/pubs/2007-06-10-PLDI-DSA.html ). However, my "Percent May Alias" for all the benchmarks is much greater, especially "bzip2". The DSA code I use is

Hi Alexandre, On Wed, Oct 19, 2016 at 11:19 AM, Alexandre Isoard <alexandre.isoard at gmail.com> wrote: > I am probably missing something important, but what I mean is that you can > always convert: > > %y = xor %x, %x > to > %y = 0 > > Regardless of if %x is/might be an undef. That is, consider that reading %x > any number of times always give the value of its

On Thu, 2008-03-27 at 09:51 -0600, John Regehr wrote: > Hey, you need to be careful with this reasoning or else you'll end up > implementing a whole new language, compiler, and OS. > > Oh wait nevermind :). Don't forget prover. :-) shap

Hi Mehdi, On Wed, Oct 19, 2016 at 8:29 PM, Mehdi Amini <mehdi.amini at apple.com> wrote: >> sext(x): >> t = zext x >> result = 0 >> for i = 0 to bitwidth: >> result |= t << i; >> return result > > I don’t understand this definition of sext? > Are you trying to express that we will copy the sign one bit at a time, and so every `new`