similar to: [LLVMdev] SCEV Question

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

Hi Fellows, The goal is to find the induction variable for a loop, where the induction variable increments with the multiplication, division or shift operations, like this one: sz = 8; do { ... ... sz = sz / 2; } while (sz) Is SCEV capable of detecting the induction variable 'sz' in this case? The code snippet I am using to solve the problem is for each basic-block in a

The Problem? Nowaday, SCEV called "Scalar Evolution" does only evolate instructions that has predictable operand, Constant-Based operand. such as that can evolute as a constant. otherwise we couldn't evolate it as SCEV node, evolated as SCEVUnknown. important thing that we remember is, we do not use SCEV only for Loop Deletion, which that doesn't really needed on nature loops

I've been doing some digging in this area (scev, wrapping arithmetic), learning as much as I can, and have reached a point where I'm fairly confused about the semantics of nuw in scalar evolution expressions. Consider the following program: define void @foo(i32 %begin) { entry: br label %loop loop: %idx = phi i32 [ %begin, %entry ], [ %idx.dec, %loop ] %idx.dec = sub nuw i32

[+CC Andy] Hi Elena, I don't have any fundamental issues with teaching SCEV about floating point types, but given this will be a major change, I think a high level roadmap should be discussed on llvm-dev before we start reviewing and committing changes. Here are some issues that I think are worth discussing: - Core motivation: why do we even care about optimizing floating point

Hi Sanjoy, SCEV is behaving inconsistently when forming SCEV for this zext instruction in the attached test case- %conv5 = zext i32 %dec to i64 If we request a SCEV for the instruction, it returns- (zext i32 {{-1,+,1}<nw><%for.body>,+,-1}<nw><%for.body7> to i64) This can be seen by invoking- $ opt -analyze -scalar-evolution inconsistent-scev-zext.ll But when computing

Hi, +CC Max, Serguei This looks like a textbook case of why caching is hard. We first call getZeroExtendExpr on %dec, and this call does end up returning an add rec. However, in the process of simplifying the zext, it also calls into isLoopBackedgeGuardedByCond which in turn calls getZeroExtendExpr(%dec) again. However, this second (recursive) time, we don't simplify the zext and cache a

On 8/8/2017 1:37 PM, Friedman, Eli wrote: > On 8/8/2017 10:22 AM, Geoff Berry via llvm-dev wrote: >> Hi all, >> >> I'm looking into resolving a FIXME in the LoopDataPrefetch (and FalkorMarkStridedAccesses) pass by marking both of these passes as preserving the ScalarEvolution analysis. Unfortunately, when this change is made, LSR will generate different code. One of the

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, On Tue, Aug 8, 2017 at 12:58 PM, Friedman, Eli <efriedma at codeaurora.org> wrote: > Oh, I see... yes, we do stupid things involving mutating NoWrap flags after > a SCEV is created. (grep for setNoWrapFlags in ScalarEvolution.cpp.) That's really a compile time hack -- we defer some expensive tricks to prove nsw/nuw on an add recurrences to when we've been asked to

On Fri, 2011-11-11 at 23:55 +0100, Tobias Grosser wrote: > On 11/11/2011 11:36 PM, Hal Finkel wrote: > > On Thu, 2011-11-10 at 23:07 +0100, Tobias Grosser wrote: > >> On 11/08/2011 11:29 PM, Hal Finkel wrote: > >> Talking about this I looked again into ScalarEvolution. > >> > >> To analyze a load, you would do: > >> > >> LoadInst *Load

How do you generate a SCEVAddRecExpr from a SCEV? It tried dyn_casting and it seems like that the SCEV returned by getSCEV is not a SCEVAddRecExpr. Thanks On Fri, Sep 30, 2016 at 4:16 PM, Friedman, Eli <efriedma at codeaurora.org> wrote: > On 9/30/2016 12:16 PM, Charith Mendis via llvm-dev wrote: > >> >> Hi all, >> >> What is the best way to get the symbolic

Sorry typo in test case, Please ignore previous mail. Consider below case: for (j=1; j < itr; j++) { - - - - for (i=1; i < itr; i++) { { temp= var[i << 1]; - - - - - } } In the above example, we are unable to get "SCEVAddRecExpr" for "var[i << 1]" Its "SCEVAddRecExpr" is computable in *Outer Loop* I

Hi all, What is the best way to get the symbolic expression for an address calculation in llvm specially when memory addresses are calculated within a loop. Use case: I want to know what loop induction variables are used for a particular address calculation and in what symbolic context. Thereby, I want to identify which stores and loads will be contiguous in memory if I unroll each of the

Hi! I would appreciate some feedback from someone with experience in SCEV/SE. D39346 tries to fix an issue in LV (PR34965) that exposes a limitation in SCEV/SE. The best solution to the LV issue might not be a fix at SCEV/SE level but we may want to report/address SCEV/SE limitation as well. For the snippet below, LV expects SE to return a SCEVAddRecExpr for %21. However, SE returns ((4 * (zext

Hello all, I wanted to get some feedback on this patch for ScalarEvolution. It addresses a performance problem I am seeing for simple benchmark. Starting with this C code: 01: signed char foo(void) 02: { 03: const int count = 8000; 04: signed char result = 0; 05: int j; 06: 07: for (j = 0; j < count; ++j) { 08: result += (result_t)(3); 09: } 10: 11: return result; 12: } I

On 11/12/2011 12:11 AM, Hal Finkel wrote: > On Fri, 2011-11-11 at 23:55 +0100, Tobias Grosser wrote: >> On 11/11/2011 11:36 PM, Hal Finkel wrote: >>> On Thu, 2011-11-10 at 23:07 +0100, Tobias Grosser wrote: >>>> On 11/08/2011 11:29 PM, Hal Finkel wrote: Talking about this I >>>> looked again into ScalarEvolution. >>>> >>>> To

Hi Geoff, On Wed, Aug 9, 2017 at 8:58 AM, Geoff Berry <gberry at codeaurora.org> wrote: > On 8/8/2017 8:38 PM, Sanjoy Das wrote: >> >> Hi, >> >> On Tue, Aug 8, 2017 at 12:58 PM, Friedman, Eli <efriedma at codeaurora.org> >> wrote: >>> >>> Oh, I see... yes, we do stupid things involving mutating NoWrap flags >>> after

I now understand that IndVarSimplify.cpp is capable of reproducing array references when the pointer initialization from the array address is found inside the immediately enclosing loop, such that in the following code: int A[20000], B[100], Z; int main() { int i, j, *a, *b; for ( a = &A[0], i = 0; i != 200; i++ ) for ( b = &B[0], j = 0; j != 100; j++

> On Aug 14, 2017, at 7:35 AM, Geoff Berry <gberry at codeaurora.org> wrote: > > Hi Sanjoy, > > [adding Adam since I believe he added the original FIXME to preserve SCEV > in LoopDataPrefetch] For record, that wasn’t me. It was there from the beginning when Hal added the PPC-specific pass. Adam > > On 8/14/2017 1:36 AM, Sanjoy Das wrote: >> Hi Geoff,