similar to: Analyze SCEV expression after IR is removed clarification

Hi, We come across a ScalarEvolution (SE) problem the other day. It seems to be a fundamental design problem. I don't think I have a clean and cheap fix to this problem. I talked with Andy in the phone yesterday, he told me it is a known fundamental problem. But I don't see any discussion on this problem on the list, so I post the problem here, soliciting your insightful comment.

On Fri, 20 Apr 2007, Dan Gohman wrote: > The SCEV framework sorts operands of commutative SCEVs by their > getSCEVType() value, and then does an ad-hoc sort to group repeated > operands, but it does not do a full sort. In some test cases I'm > looking at right now, this causes it to miss opportunities to reuse > SCEV objects, as in cases like this: > > ( %i + %r54 +

The SCEV framework sorts operands of commutative SCEVs by their getSCEVType() value, and then does an ad-hoc sort to group repeated operands, but it does not do a full sort. In some test cases I'm looking at right now, this causes it to miss opportunities to reuse SCEV objects, as in cases like this: ( %i + %r54 + %r59) ( %r54 + %r59 + %i) As a result, passes like LoopStrengthReduce

On Fri, Apr 20, 2007 at 03:16:03PM -0700, Chris Lattner wrote: > > The obvious solution would be to sort the values. Many SCEV types could > > be ordered in reasonable ways, though for SCEVUnknown it would require > > an ordering for Value objects, and I don't really want this to get > > complicated. I'm considering just using getValueID() as a primary sort >

The Loop Strength Reduction pass appears to break debug information even for the most basic input. I believe this is a well known issue already (see https://bugs.llvm.org/show_bug.cgi?id=38815) but I also believe that it deserve some extra attention. Consider the following input compiled with 'clang -g -O3 foo.c -mllvm -print-after-all' --- void foo(unsigned char *p) { #pragma clang loop

Tobias Grosser wrote: > You create a map from the old_loop to a symbolic expression. What type would > this symbolic expression have? Would it be a SCEVExpr? evaluateAtIteration takes a scev, so apply will take a scev, or a map (loop->scev). You can always build a ScevUnknown from an SSA name and use that in the apply. > At the moment, we calculate at the beginning of each >

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

Hi, I noticed an inconsistency in how ScalarEvolution orders instruction operands. This inconsistency can result in creation of separate (%a * %b) and (%b * %a) SCEVs as demonstrated by the example IR below (attached as gep-phi.ll)- target datalayout = "e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128" define void @foo(i8* nocapture %arr, i32 %n, i32* %A, i32* %B) local_unnamed_addr {

Hi Preston, I was wondering ... "Bottom" is a bit overloaded as far as terms go. Would SCEVNaN be a better name for this beast? Sameer. > -----Original Message----- > From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] On > Behalf Of Sameer Sahasrabuddhe > Sent: Monday, October 08, 2012 9:16 AM > To: preston.briggs at gmail.com > Cc: LLVM

On Sun, 7 Oct 2012 18:53:59 -0700 Preston Briggs <preston.briggs at gmail.com> wrote: > I'd like a value, call it Bottom, such that > > SE->getAddExpr(Bottom, X) => Bottom > SE->getMulExpr(Bottom, X,) => Bottom > isKnownPredicate(any, Bottom, X) => false > etc. > > > I can write code to make NULL work like I want, but it would be > simpler

Thanks for fixing this Sanjoy! I do have a few questions/suggestions on the fix if you don't mind. 1) Would this work correctly if the values are call instructions with no operands, like this- %a = foo() %b = bar() 2) From the way this function is set up, it looks like the emphasis is on saving compile time by trading off robustness. Is compile time such a big concern here that we want to

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 root causes seems to be that SCEV will return different nsw/nuw flags for the same Value, depending on what order the

On Fri, 23 Feb 2007, Dan Gohman wrote: > I'm experimenting a bit with the SCEV code and one of the problems I'm > facing is that there's no way to represent a getelementptr operation as a > SCEV. Right. SCEV is really designed to expression integer equations. > The obvious way to do this in the existing SCEV framework is to add > a new SCEV subclass. I started doing

On Fri, Nov 30, 2012, at 08:46 PM, Sebastian Pop wrote: > Hi Tobi, > > I would like to remove the SCEVRewriter code and replace it with a call > to > SCEVAddRec::apply (see attached a patch that adds just this function). > More > precisely I want to add another function called apply_map that applies a > map > (loop -> expr) on a given scev. This is the apply

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

I have a few questions regarding cost calculation in loop strength reduction. 1. Ignoring LSR uses of kind ICmpZero. These usually come from the loop latch conditions. On Hexagon most loops that would contain such a LSR use are going to be converted to hardware loops and the entire check will disappear. There is no need to analyze these cases in LSR. In fact, completely ignoring them improves

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

Hi Max, On Wed, Jan 24, 2018 at 10:03 PM, Maxim Kazantsev via llvm-dev <llvm-dev at lists.llvm.org> wrote: > I want to raise a discussion about reasonability of late setting of > nsw/nuw/nw flags to SCEV AddRecs through setNoWrapFlags method. A discussion > about this have already happened in August last year, there was a concern > about different no-wrap flags that come from

Hi, I think these two patches are related to the topic: https://reviews.llvm.org/D41578 “[SCEV] Do not cache S -> V if S is not equivalent of V” * It’s committed. It can cause generation of redundant instructions. We’ve got regressions due to it. The biggest one is 7.31% regression in Spec2k6 401.bzip2 on Cortex-A57(AArch64). https://reviews.llvm.org/D42290 “[SCEV] Clear poison flags

On Thu, Jan 25, 2018 at 9:55 PM, Maxim Kazantsev <max.kazantsev at azul.com> wrote: > I don't really believe that option 2 may work just because even if we recalculate the range for this add recurrency, there are already its derivatives with cached ranges (the most obvious example is sext and expressions where this sext is involved). We can speculate about what is "simple