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...le, there could be an infinite loop in-between. Strong post-dominance makes the stronger guarantee that there will be no infinite loop from B to A. Do we have anything in LLVM for determining strong post-dominance and in general for guaranteeing that if B is executed, then A will also be executed? Bjarke -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20150708/ac55c312/attachment.html>

...plot(df1[[i]], ylab=i) but can it somehow be achieved bu using lapply? I would be hoping for something like lapply(df1, function(x) plot(x, ylab=parent.index())) or some way to parse the index number out of the call, using match.call() or something like that. Thanks in advance for any comments, Bjarke Christensen

----- Original Message ----- > From: "Bjarke Roune" <broune at google.com> > To: "Jingyue Wu" <jingyue at google.com> > Cc: llvmdev at cs.uiuc.edu > Sent: Tuesday, June 30, 2015 8:16:13 PM > Subject: Re: [LLVMdev] Deriving undefined behavior from nsw/inbounds/poison for scalar evolution > > Hi Ad...

...ore expensive ( https://llvm.org/bugs/show_bug.cgi?id=21148). For this reason, we disabled indvar widening in NVPTX in http://reviews.llvm.org/D6196. Hope it helps. Jingyue On Mon, Jun 29, 2015 at 11:59 AM Adam Nemet <anemet at apple.com> wrote: > > > On Jun 26, 2015, at 4:01 PM, Bjarke Roune <broune at google.com> wrote: > > > > *** Summary > > I'd like to propose (and implement) functionality in LLVM to determine > when a poison value from an instruction is guaranteed to produce undefined > behavior. I want to use that to improve handling of ns...

...ucing an analysis pass for strong post-dominance (as opposed to the usual kind of post-dominance). There was a brief amount of discussion on this a while back: https://groups.google.com/forum/#!topic/llvm-dev/CBJY51__wOE I don't know if there's been any developments on that since then. Bjarke -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20160412/7ed21a02/attachment.html>

----- Original Message ----- > From: "Bjarke Roune" <broune at google.com> > To: "Hal Finkel" <hfinkel at anl.gov> > Cc: llvmdev at cs.uiuc.edu, "Jingyue Wu" <jingyue at google.com> > Sent: Wednesday, July 1, 2015 2:27:59 PM > Subject: Re: [LLVMdev] Deriving undefined behavior from nsw/i...

Hi Bjarke, Bjarke Walling wrote: > I see. So you check this value stored in a thread-local variable after > each call? And you lower invoke to a call and branch with regard to > this value? > Yes, that's correct. > What are these sophisticated techniques you are talking about? My ti...

...thought that instead of the runtime created lookup table you could encode it as jmp instructions after each call. It is like the optimisation of malloc/free where you write a size value just before the allocated memory block. The memory is in itself a hash table if the hashes are memory locations. Bjarke Walling

...tion for recurrences when the loop header dominates the entire loop, the instruction with nsw post-dominates the loop header and undefined behavior is guaranteed on wrap via the poison value analysis pass that I'd like to write. What do you think? Do we already have something similar to this? Bjarke *** PS: What got me thinking about this: My immediate motivation is that I'd like LSR to be able to create induction variables for expressions like &ptr[i + offset] where i and offset are 32 bit integers, ptr is a loop-invariant 64 bit pointer, i is an induction variable and offset is l...

...om> wrote: > > Hi Owen, > > This is very interesting. > > How different is "convergent" from "uniform"? An instruction is uniform if threads in the same SIMT unit (e.g. warp) do not diverge when executing this instruction. > > I ask this because Bjarke recently came up with a mathematical definition of uniformity. I wonder if that is a foundation "convergent" needs as well. AFAICT, Bjarke's definition of "uniformity" is less restrictive than "convergent". For example, it allows loop unswitching the following cod...

This concerns me as well. I've accepted a programming bounty to port LLVM to AROS x86. Once that's done I suspect many people will want it ported to the other processors AROS supports. ----- Original Message ---- > From: Bjarke Walling <bjarke.walling at gmail.com> > To: cfe-dev at cs.uiuc.edu > Sent: Sat, April 9, 2011 2:06:30 PM > Subject: [cfe-dev] Adding new target for hobby OS > > Hi, > > I'm contemplating using Clang for my hobby OS project called > "wkernel". I want t...

Hi Duncan, Hi Bjarke, Duncan Sands wrote: > Take a look at libunwind (http://www.hpl.hp.com/research/linux/libunwind/). > Another possibility, very close you yours and currently used by the vmkit > project, is to modify all functions so they return two values, the usual > return value and an additional bo...

...ven possible to insert jmp instructions without them being optimized away? I also need to access information about the call frame. My last question: Is it possible to implement a flag for the back-end that selects which kind of exception handling to use? Ie. my idea versus DWARF + libgcc. Cheers, Bjarke Walling

Bjarke Walling wrote: > Another option I'm thinking about is creating a runtime that, when > initialized, compiles the DWARF information to native code. It could > create an Instruction Pointer lookup hash table associated with unwind > actions. JIT-compiling the unwinder data, yes. Gi...

Hi Bjarke, > * Provide an efficient runtime implementation that does not > depend on reading the DWARF EH information. why? The DWARF EH info encodes two things: (1) how to restore registers; and (2) matching rules for exception objects, and what to do with them. You will need something alon...

Hello, Bjarke > * Provide a pass that raises C++ exception handling to just > unwind instructions and thread-local data. Are you familiar with C++ EH? How would you handle catches? Cleanups? > Other call frames might be more complex to handle. It depends on the > moves needed to restore the r...

Hey Sanjoy, Thanks for the quick repsonse. On 04/10, Sanjoy Das wrote: > [+CC Bjarke who wrote getNoWrapFlagsFromUB + related bits] Also thanks. > One fundamental reason why we cannot reason about NoWrap flags in SCEV > for arithmetic outside of loops is to avoid issues like this: > > if (cond) { > val[x +nsw y] = 42; > } else { > val[x + y] = 42; > }...

Hi all, In light of recent discussions regarding updating passes to respect convergent semantics, and whether or not it is sufficient for barriers, I would like to propose a change in convergent semantics that should resolve a lot of the identified problems regarding loop unrolling, loop unswitching, etc. Credit to John McCall for talking this over with me and seeding the core ideas. Today,

Hello, I was wondering under which circumstances ScalarEvolution will propagate the no wrap flags from binary operators. In particular I looked at non-loop carried code, e.g., as in the following function: int add(int x, int y) { return x + y; } for which clang uses an "add nsw" instruction but ScalarEvolution does not propagate this information. The -analyze output looks like this:

Hi Sanjoy, thanks for your thoughts on this. On Sat, Jun 27, 2015 at 12:16 AM, Sanjoy Das <sanjoy at playingwithpointers.com > wrote: > > First of all, going by the "poison causes UB only when observed", SCEV > does not do the right thing currently: [...] > > That seems like a bug? There's also bug 23527 for GEP. Sounds like there might be more such bugs. One