similar to: [LLVMdev] [RFC] SCEV Enhancements

On Feb 23, 2012, at 8:20 AM, David Greene wrote: > I have a few enhancements to SCEV to help it identify more types of > recurrences. I want to send these upstream but I need a little > feedback. > > I've added ptrtoint and inttoptr SCEV expressions so that recurrences > involving these constructs can be recognized. However, this scary > comment gives me pause: >

Dan Gohman <gohman at apple.com> writes: >> These enhancements are critical for us because of the way our frontends >> work (less than ideal but we have to deal with it), due to some language >> quirks (casting in C, odd Fortran constructs, etc.) and because users >> sometimes stretch the boundaries of good taste :). >> >> Is this a reasonable approach?

LLVM 2.7's ScalarEvolution.cpp has this scary comment: // It's tempting to handle inttoptr and ptrtoint as no-ops, however this can // lead to pointer expressions which cannot safely be expanded to GEPs, // because ScalarEvolution doesn't respect the GEP aliasing rules when // simplifying integer expressions. I think I understand what the comment is saying. If a GEP has

On Sep 9, 2010, at 1:48 PM, David Greene wrote: > LLVM 2.7's ScalarEvolution.cpp has this scary comment: > > // It's tempting to handle inttoptr and ptrtoint as no-ops, however this can > // lead to pointer expressions which cannot safely be expanded to GEPs, > // because ScalarEvolution doesn't respect the GEP aliasing rules when > // simplifying integer

On Feb 24, 2012, at 9:53 AM, David A. Greene wrote: > Dan Gohman <gohman at apple.com> writes: > >>> These enhancements are critical for us because of the way our frontends >>> work (less than ideal but we have to deal with it), due to some language >>> quirks (casting in C, odd Fortran constructs, etc.) and because users >>> sometimes stretch the

Hi, > Is there a document describing the guts of SCEV anywhere? If you're looking for theoretical background of SCEV (chains of recurrences algebra), you may take a look at this article: http://citeseer.ist.psu.edu/vanengelen00symbolic.html I'm not aware of any LLVM-specific document describing SCEV. > I have a simple question. When looking at a linear SCEVAddRecExpr > with a

On 06/20/2017 03:26 AM, Hal Finkel wrote: > Hi, Adrien, Hello Hal! Thanks for your answer! > Thanks for reporting this. I recommend that you file a bug report at > https://bugs.llvm.org/ Will do! > Whenever I see reports of missed optimization opportunities in the face > of ptrtoint/inttoptr, my first question is: why are these instructions > present in the first place? At

Hello all, There is a missing vectorization opportunity issue with clang 4.0 with the file attached. Indeed, when compiled with -O2, the "op_distance" function get vectorized, but not the "op" one. For information, this test case has been reduced from a file generated by the Pythran compiler (https://github.com/serge-sans-paille/pythran). If we take a look at the generated

Is there a document describing the guts of SCEV anywhere? I have a simple question. When looking at a linear SCEVAddRecExpr with a constant step recurrence (that is, getStepRecurrence returns SCEVConstant), is the constant in terms of bytes or in terms of "index," in that the byte offset is calculated by taking the step and multiplying it by the data size of any memory operation its

On Fri, Jun 15, 2007 at 04:16:57PM +0200, Florian Brandner wrote: > hi, > > > Florian Brandner wrote: > > Dan Gohman wrote: > >> On Wed, May 23, 2007 at 12:23:38AM -0700, Chris Lattner wrote: > >>> Right. The original Value*'s are preserved in the DAG, but dropped when > >>> MachineInstrs are created. We could add a machineoperand to

hi, Florian Brandner wrote: > Dan Gohman wrote: >> On Wed, May 23, 2007 at 12:23:38AM -0700, Chris Lattner wrote: >>> Right. The original Value*'s are preserved in the DAG, but dropped when >>> MachineInstrs are created. We could add a machineoperand to capture this >>> Value* if desired. >> Another benefit of keeping the original Value*'s

On Jul 22, 2009, at 1:30 PM, Dan Gohman wrote: > Hello, > > I'm working on refining the definition of getelementptr (GEP) to > clarify its semantics and to allow front-ends to provide additional > information to optimization passes. It would be quite valuable to have cleaner semantics for GEPs, both for LLVM in general and for the memory safety work we have been doing in

Thanks for the feedback, Sanjoy. > SCEV is fairly conservative around PHI nodes that aren't recurrences and aren't obviously equivalent to a min-max branch-phi idiom. Is that the limitation you're running into here? Yes, that's exactly the problem. The problematic PHI nodes (%bc.resume.val and %bc.resume.val1) aren't either recurrences or related to min-max idioms. I

Hi again. I have a complex type system in my custom language that isn't easily representable as LLVM IR types, so I figured I could mostly get along with treating my types as i8* and doing the appropriate bitcasts and inttoptr instructions, and doing pointer arithmetic myself (by casting the pointers to ints, adding the appropriate byte offsets, and then casting back to pointers). However,

On 4/20/11 10:08 AM, Jianzhou Zhao wrote: > I have a question about when we should apply these pointer aliasing > rules. Do the rules tell us when a load/store is safe? > "Any memory access must be done through a pointer value associated > with an address range of the memory access, otherwise the behavior is > undefined." I don't think the pointer aliasing rules

I have a question about when we should apply these pointer aliasing rules. Do the rules tell us when a load/store is safe? "Any memory access must be done through a pointer value associated with an address range of the memory access, otherwise the behavior is undefined." So this means the conversion discussed here is still safe in terms of memory safety, but its meaning after conversion

Hi again, So I finally gave up on trying to get through the converting (x86' push pop mov add) because it deals a lot with crazy pointer arithmetics and sonce inttoptr and ptrtoint doesn't provide any alias analysis information. Daniel, you said it doesn't make much sense to provide it but in my cases it is actually very much needed, you didn't say it wasn't possible to

On Sep 13, 2012, at 12:00 PM, Mon Ping Wang <monping at apple.com> wrote: >>> In C, integer to point conversions are implementation defined and >>> depends on what the addressing structure of the execution environment >>> is. Given the current definition of ptrtoint and intoptr, I feel that >>> the addressing structure feels like a flat memory model

On Wed, Apr 20, 2011 at 12:20 PM, Eli Friedman <eli.friedman at gmail.com> wrote: > On Wed, Apr 20, 2011 at 8:08 AM, Jianzhou Zhao <jianzhou at seas.upenn.edu> wrote: >> I have a question about when we should apply these pointer aliasing >> rules. Do the rules tell us when a load/store is safe? >> "Any memory access must be done through a pointer value

> -----Original Message----- > From: Mon Ping Wang [mailto:monping at apple.com] > Sent: Thursday, September 13, 2012 1:55 AM > To: Villmow, Micah > Cc: llvmdev at cs.uiuc.edu > Subject: Re: [LLVMdev] Proposal: New IR instruction for casting between > address spaces > > > On Sep 12, 2012, at 2:45 PM, "Villmow, Micah" <Micah.Villmow at amd.com> >