similar to: ScalarEvolution "add nsw" question

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 Johannes, Sanjoy has given you great information already. On Sun, Apr 10, 2016 at 5:19 PM, Sanjoy Das <sanjoy at playingwithpointers.com> wrote: > Johannes Doerfert wrote: > > Is there any plan to use e.g., post-dominance information to > > propagate wrapping flags? > > None that I'm aware of. > > > If x +nsw y post-dominates the entry block > >

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

Hi folks, I'm trying to analyse this piece of IR: for.body: ; preds = %for.body, %entry %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ] %0 = shl nsw i64 %indvars.iv, 1 %arrayidx = getelementptr inbounds i32* %b, i64 %0 %1 = load i32* %arrayidx, align 4, !tbaa !1 %add = add nsw i32 %1, %I %arrayidx3 = getelementptr

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

> 1. Callers are expected to not engage in speculation. ScalarEvolution > itself must only create expressions it knows hold in all cases. This is correct. There is some more relevant text in ScalarEvolution::isSCEVExprNeverPoison. And you're right, this is quite restrictive. > Long term, I think that it would be cleaner to rework this so that all of the SCEV's are immutable

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

Hello to everybody, I'm working on some improvements on trip count computation with ScalarEvolution analysis. Considering the following test ;----------------------------------------------------------------------------; define void @foo(i32 %a, i32 %b, i32 %s) #0 { entry: %cmp = icmp sgt i32 %s, 0 %cmp15 = icmp sgt i32 %a, %b %or.cond = and i1 %cmp, %cmp15 br i1 %or.cond, label

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

On Oct 1, 2013, at 6:45 AM, Michele Scandale <michele.scandale at gmail.com> wrote: > Hello to everybody, > > I'm working on some improvements on trip count computation with ScalarEvolution > analysis. > Considering the following test > > ;----------------------------------------------------------------------------; > define void @foo(i32 %a, i32 %b, i32 %s) #0

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

Is that why we do not deduce +<nsw> from "add nsw" either? Is that an intrinsic limitation of creating a context-invariant expressions from a Value* or is that a limitation of our implementation (our unification not considering the nsw flags)? On Wed, Aug 15, 2018 at 12:39 PM Friedman, Eli <efriedma at codeaurora.org> wrote: > On 8/15/2018 12:21 PM, Alexandre Isoard via

I'm not sure I understand the poison/undef/UB distinctions. But on this example: define i32 @func(i1 zeroext %b, i32 %x, i32 %y) { > entry: > %adds = add nsw i32 %x, %y > %addu = add nuw i32 %x, %y > %cond = select i1 %b, i32 %adds, i32 %addu > ret i32 %cond > } It is important to not propagate the nsw/nuw between the two SCEV expressions (which unification would

Hello, If I run clang on the following code: void func(unsigned n) { > for (unsigned long x = 1; x < n; ++x) > dummy(x); > } I get the following llvm ir: define void @func(i32 %n) { > entry: > %conv = zext i32 %n to i64 > %cmp5 = icmp ugt i32 %n, 1 > br i1 %cmp5, label %for.body, label %for.cond.cleanup > for.cond.cleanup:

Ok. To go back to the original issue, would it be meaningful to add a SCEVUMax(0, BTC) on the final BTC computed by SCEV? So that it does not use "negative values"? On Wed, Aug 15, 2018 at 2:40 PM Friedman, Eli <efriedma at codeaurora.org> wrote: > On 8/15/2018 2:27 PM, Alexandre Isoard wrote: > > I'm not sure I understand the poison/undef/UB distinctions. >

Thanks for the suggestion but datalayout info did not solve the problem! -Pankaj -----Original Message----- From: Philip Reames <listmail at philipreames.com> Sent: Tuesday, August 20, 2019 5:26 PM To: Chawla, Pankaj <pankaj.chawla at intel.com>; llvm-dev at lists.llvm.org Subject: Re: [llvm-dev] missing simplification in ScalarEvolution? Try adding a datalayout with pointer size

> 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,

Hi Sanjoy, Thanks for the reply! Your approach sounds good to me! I think 1) is legal as address wraparound in unsigned range doesn't make sense given a positive offset, but I am not sure. I think umax will not be added if we can prove the predicate as known. I am not sure whether umax will get simplified if we add nuw to the expressions. -Pankaj -----Original Message----- From: Sanjoy

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

I am testing vectorization on the following test case: float x[1024], y[1024]; void myloop1() { for (long int k = 0; k < 512; k++) { x[2*k] = x[2*k]+y[k]; } } Vectorization failed due to "unsafe dependent memory operation". I traced the LoopAccessAnalysis.cpp and found the reason is the NoWrapFlag for SCEVAddRecExpr is not set and consequently the