similar to: UB and known bits

While looking at optimizations where Souper exploits known bits, I realized that it would be easy to teach Souper to compute known bits. Comparing its results against computeKnownBits() from r246393, it looks like there are some easy (and some not-easy) opportunities for improvement, please see a few examples below. The expressions come from compiling LLVM itself. Happily, this exercise

In the section about poison values, the LLVM language reference manual says: "Values other than phi nodes depend on their operands." This implies that a select instruction's output can be poisoned by its not-selected argument value. If select were poisoned only by its selected argument, we would expect this fact to be mentioned specifically, as it is for phi. Next I'll

> Interesting. Do you happen to have some examples laying around? Sorry, no, I'll have to re-run. I felt that the select-heavy results were sort of humorous and clever at first, but then just annoying. > Except for decode-limited situations, in general decreasing the critical path length is more important > than eliminating instructions. The critical path length is a

----- Original Message ----- > From: "David Majnemer" <david.majnemer at gmail.com> > To: "Hal Finkel" <hfinkel at anl.gov> > Cc: "Pete Cooper" <peter_cooper at apple.com>, "LLVMdev" <llvmdev at cs.uiuc.edu> > Sent: Wednesday, July 1, 2015 7:17:19 PM > Subject: Re: [LLVMdev] extractelement causes memory access violation

On 07/22/2015 01:28 PM, Sean Silva wrote: > > > On Wed, Jul 22, 2015 at 12:54 PM, Hal Finkel <hfinkel at anl.gov > <mailto:hfinkel at anl.gov>> wrote: > > One thing that is important to consider is where in the pipeline > these kinds of optimizations fit. We normally try to put the IR > into a canonical simplified form in the mid-level optimizer.

----- Original Message ----- > From: "Pete Cooper" <peter_cooper at apple.com> > To: "Hal Finkel" <hfinkel at anl.gov> > Cc: "LLVMdev" <llvmdev at cs.uiuc.edu>, "Paweł Bylica" <chfast at gmail.com> > Sent: Wednesday, July 1, 2015 6:42:41 PM > Subject: Re: [LLVMdev] extractelement causes memory access violation - what to

I don't know how things work at the moment, but it seems to me that you can do lots of sensible things, and avoid lots of silly things, if you keep track of four possible values for each bit: - undef (the default) - poison - known to be 0 - known to be 1 This makes both David's and Chandler's examples work nicely if you assume: - ZEXT makes all the new bits known 0 - SEXT makes all

I'm looking at the output of memcmp() expansion (D34904), and I noticed that there are many ways to produce the common positive/zero/negative comparison result in IR. For the following 6 functionally equivalent C source functions, we produce 6 different versions of IR which leads to 6 different asm outputs for x86. Which of these should we choose as canonical IR form? 1. Two selects int

Cool! Looks like we do lots of provably unnecessary alignment checks. :) On Tue, Nov 25, 2014 at 9:03 AM, John Regehr <regehr at cs.utah.edu> wrote: > Actually, let me save you some time by pointing out the thing that is > perhaps immediately useful about our recent work, which is the fact that > Souper now supports "optimization profiling". > > If you build an

I hope there's some useful material in here! http://blog.regehr.org/archives/1192 John

We (the folks working on Souper) would appreciate any feedback on these IR-level superoptimizer results: http://blog.regehr.org/extra_files/souper-jul-15.html My impression is that while there's clearly plenty of material in here that doesn't want to get implemented in an opt pass, there are a number of gems hiding in there that are worth implementing. Blog post containing

> I just noticed: most of the results in this batch seem to be about exploiting `[zs]ext i1` having cost 1 > in order to replace a select of cost 3. > Could you do a run where select has cost 1 and [zs]ext i1 (and trunc to i1) has cost 2 or 3? I tried this (or something quite similar) earlier and it caused Souper to introduce *a lot* of selects. So the problem is that Souper's

Hello. When I run smbpasswd from samba 3.0.23a on a MIPSEL system running Linux 2.4.20 as root, I'm NEVER asked for a password. Even when I create a new user in smbpasswd, I'm not asked: root@HD.bei.digitalprojects.com:/etc/samba# strings smbpasswd root:0:AAD3B435B51404EEAAD3B435B51404EE:31D6CFE0D16AE931B73C59D7E0C089C0:[U ]:LCT-44D63D42:

I've always found the name ComputeMaskedBits a bit unintuitive, and since r154011 it's even worse because there is no masking going on whatsoever: http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20120402/140280.html Is there any appetite for a global rename to ComputeKnownBits? Or any other better names? Thanks, Jay.

Hello I am running a net work with a NT4PDC a NT4 BDC and attent to add samba BDC. I am following the brief section 28 of the Samba-Howto collection for samba head/3.0. * Adding the samba server as a BDC from NT server manager seems OK * Getting, recording domain sid is ok (see below) > rpcclient NT4PDC -U Administrator password: > lsaquery domain IMAGERIE has sid blablabla > net

On 13 May 2014 21:27, Rafael Espíndola <rafael.espindola at gmail.com> wrote: > On 13 May 2014 14:33, Jay Foad <jay.foad at gmail.com> wrote: >> I've always found the name ComputeMaskedBits a bit unintuitive, and >> since r154011 it's even worse because there is no masking going on >> whatsoever: >> >>

When I used smbpasswd it gives me the following error... root at hayek:~# smbpasswd john New SMB password: Retype new SMB password: Failed to find entry for user john. This is despite the existence of the user root at hayek:~# cat /etc/samba/smbpasswd # # SMB password file. # nobody:65534:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX:[U ]:LCT-00000000:nobody

On Dec 23, 2014, at 10:28 AM, Chris Bieneman <beanz at apple.com> wrote: >>> It should be straight-forward to have something like LLVMInitializeX86Target/RegisterTargetMachine install the intrinsics into a registry. >> >> I tried doing that a few years ago. It’s not nearly as easy as it sounds because we’ve got hardcoded references to various target intrinsics scattered

One thing that is important to consider is where in the pipeline these kinds of optimizations fit. We normally try to put the IR into a canonical simplified form in the mid-level optimizer. This form is supposed to be whatever is most useful for exposing other optimizations, and for lowering, but only in a generic sense. We do have some optimizations near the end of our pipeline (vectorization,

Looks like LVI actually does have cases for max and min; would it be better to allow ValueTracking to use range analysis instead? - CL > On Aug 1, 2016, at 8:44 PM, Philip Reames <listmail at philipreames.com> wrote: > >> On 07/29/2016 07:08 PM, Carlos Liam via llvm-dev wrote: >> Hi all, >> >> Say we have this IR: >> >> %1 = icmp slt i16 %x, 0