similar to: [LLVMdev] New LLVM Pass

Hi, I recently looked into the LICM(Loop Invariant Code Motion) pass of LLVM and got a question about hoist load instruction to loop preheader. I would like to show two examples: Example 1: int func(int n, int *fp) { int i; int a[1000]; for (i = 0; i < n; ++i) { a[i] += *fp; // load from *fp pointer, no hoist } } Here, load *fp CAN NOT be hoisted to loop preheader. If replace *fp

On Thu, Apr 25, 2013 at 9:18 AM, Arnold Schwaighofer < aschwaighofer at apple.com> wrote: > > On Apr 25, 2013, at 10:51 AM, Preston Briggs <preston.briggs at gmail.com> wrote: > > > It's an interesting problem. > > The best stuff I've seen published is by Cooper, Eckhart, & Kennedy, in PACT '08. > > Cooper gives a nice intro in one of his

As far as I can understand of the code, the Reassociate tries to achieve this result by its "ranking" mechanism. If it dose not, it is not hard to achieve this result, just restructure the expression in a way such that the earlier definition of the sub-expression is permute earlier in the resulting expr. e.g. outer-loop1 x= outer-loop2 y =

On Apr 23, 2013, at 10:37 AM, Shuxin Yang <shuxin.llvm at gmail.com> wrote: > As far as I can understand of the code, the Reassociate tries to achieve this result by its "ranking" mechanism. > > If it dose not, it is not hard to achieve this result, just restructure the expression in a way such that > the earlier definition of the sub-expression is permute earlier in

On Apr 25, 2013, at 10:51 AM, Preston Briggs <preston.briggs at gmail.com> wrote: > It's an interesting problem. > The best stuff I've seen published is by Cooper, Eckhart, & Kennedy, in PACT '08. > Cooper gives a nice intro in one of his lectures: http://www.cs.rice.edu/~keith/512/2012/Lectures/26ReassocII-1up.pdf > I can't tell, quickly, what's going on

Hi, I am investigating a performance degradation between llvm-3.1 and llvm-3.2 (Note: current top-of-tree shows a similar degradation) One issue I see is the following: - 'loop invariant code motion' seems to be depending on the result of the 'reassociate expression' pass: In the samples below I observer the following behavior: Both start with the same expression: %add = add

It's an interesting problem. The best stuff I've seen published is by Cooper, Eckhart, & Kennedy, in PACT '08. Cooper gives a nice intro in one of his lectures: http://www.cs.rice.edu/~keith/512/2012/Lectures/26ReassocII-1up.pdf I can't tell, quickly, what's going on in Reassociate; as usual, the documentation resolutely avoids giving any credit for the ideas. Why is that?

Hello, I am working on a C++ expression templates based DSL where we are using LLVM for the code generation. I needed some help in understanding the behaviour of the LICM pass. In the following example code the "A" class is a custom container that defines various arithmetic operators using expression templates. We are defining three arrays of the "A" container and aggregating

On Sat, Oct 30, 2010 at 1:44 AM, Nick Lewycky <nicholas at mxc.ca> wrote: > Xinliang David Li wrote: > >> >> >> On Fri, Oct 29, 2010 at 12:26 AM, Nick Lewycky <nicholas at mxc.ca >> <mailto:nicholas at mxc.ca>> wrote: >> >> Xinliang David Li wrote: >> >> As simple as >> >> void foo (int n, double

Xinliang David Li wrote: > > > On Fri, Oct 29, 2010 at 12:26 AM, Nick Lewycky <nicholas at mxc.ca > <mailto:nicholas at mxc.ca>> wrote: > > Xinliang David Li wrote: > > As simple as > > void foo (int n, double *p, int *q) > { > for (int i = 0; i < n; i++) > *p += *q; > } > >

Hi Stefanos, Thanks for your comments. I added both as reviewer. > One question though. Are you sure that this: > This helps with LICM when instructions inside a conditional is loop invariant  > is not achieved with the current LoopRotate pass? Because AFAIK, it does. Basically it inserts > a guard (that branches to the preheader) and then passes like LICM hoist invariant

On 7/31/2013 12:20 PM, Chris Lattner wrote: > On Jul 31, 2013, at 6:53 AM, Krzysztof Parzyszek > <kparzysz at codeaurora.org <mailto:kparzysz at codeaurora.org>> wrote: >> On 7/30/2013 11:44 PM, Chris Lattner wrote: >>> >>> The canonical form should be that loop invariants are hoisted. >> >> The canonical form should not depend on the knowledge

----- Original Message ----- > From: "Ashutosh Nema" <Ashutosh.Nema at amd.com> > To: "songlh" <songlh at cs.wisc.edu>, llvmdev at cs.uiuc.edu > Sent: Wednesday, February 11, 2015 3:20:27 AM > Subject: Re: [LLVMdev] question about licm > > Hi, > > LICM can only hoist instructions which dominates all loop exit > blocks. > In this case

Hi all, I have a question about dereferenceable metadata on load instruction. I have a patch (https://reviews.llvm.org/D31539) for LICM that hoists loads with !invariant.group. The motivation example is devirtualization: struct A { virtual void foo(); }; int bar(); void indirect(A &a) { while(bar()) a.foo(); } With -O2 -fstrict-vtable-pointers we get: define void

On Aug 19, 2012, at 2:55 PM, "Kuperstein, Michael M" <michael.m.kuperstein at intel.com> wrote: > Hello, > > Currently, llvm::isSafeToSpeculativelyExecute() always returns false for Call instructions. > This has actual performance implications, because loop-invariant code motion makes this check, and will never hoist instructions that are not safe to speculatively

Hi Nadav, On 08/09/12 22:51, Nadav Rotem wrote: > > On Aug 19, 2012, at 2:55 PM, "Kuperstein, Michael M" > <michael.m.kuperstein at intel.com <mailto:michael.m.kuperstein at intel.com>> wrote: > >> Hello, >> Currently, llvm::isSafeToSpeculativelyExecute() always returns false for Call >> instructions. >> This has actual performance

On some targets with limited addressing modes, getting that 64-bit relocatable but loop-invariant value into a register requires several instructions. I'd like those several instruction outside the loop, where they belong. Yes, my experience is that something (I assume instcombine) recanonicalizes. Thanks, Preston On Tue, Dec 8, 2015 at 11:21 PM, Mehdi Amini <mehdi.amini at

Hello, Currently, llvm::isSafeToSpeculativelyExecute() always returns false for Call instructions. This has actual performance implications, because loop-invariant code motion makes this check, and will never hoist instructions that are not safe to speculatively execute. Unfortunately, there is currently no way to signal to LICM that a function is safe to speculatively execute. The

On Fri, Mar 31, 2017 at 10:23 AM, Sanjoy Das <sanjoy at playingwithpointers.com > wrote: > Hi Piotr, > > On March 31, 2017 at 9:07:42 AM, Piotr Padlewski > (piotr.padlewski at gmail.com) wrote: > > Hi all, > > I have a question about dereferenceable metadata on load instruction. I > > have a patch (https://reviews.llvm.org/D31539) for LICM that hoists >

Hi, TL;DR: A loop doesn't get vectorized due to the interaction of loop- rotate, licm and instcombine. What to do about it? Full story: In the benchmarks for our out-of-tree target we have a case that we would like to get vectorized, but currently it isn't. I've done some digging to see why and have some kind of idea what prevents it, but I don't know what the best way to fix