similar to: [LLVMdev] if-conversion

I am looking for advice on a problem observed with -fprofile-sample-use for samples built with the AutoFDO tool I took the "hmmer" benchmark out of SPEC2006 It is initially compiled clnag++ -o hmmer -O3 -std=gnu89 -DSPEC_CPU -DNDEBUG -fno-strict-aliasing -w -g *.c This baseline binary runs in about 164.2 seconds as reported by "perf stat" We build a sample file from this

On Thu, Jan 21, 2016 at 2:52 PM, Jonas Wagner <jonas.wagner at epfl.ch> wrote: > Hello, > > There is some data on this, e.g, in “High System-Code Security with Low > Overhead” <http://dslab.epfl.ch/proj/asap/#publications>. In this work we > found that, for ASan as well as other instrumentation tools, most overhead > comes from the checks. Especially for

Hi, It was suggested that I post my question regarding a LLVM 3.4 performance regression to this mailing list, rather than stackoverflow. So here is the link: https://stackoverflow.com/questions/22902034/llvm-3-4-performance-regressed Thanks :) Jens -- Jens Tröger http://savage.light-speed.de/

Hi, I'm coming back to this old thread with data about the performance of NOPs. Recalling that I was considering transforming NOP instructions into branches and back, in order to dynamically enable code. One use case for this was enabling/disabling individual sanitizer checks (ASan, UBSan) on demand. I wrote a pass which takes an ASan-instrumented program, and replaces each ASan check with

Hello, git bisect helped me today in tracking down a regression in LLVM/Clang. Because LLVM/Clang code is split across multiple git repositories, there were a few obstacles to overcome prior to using git bisect. I thought I would share them here, in the hope that they're useful for others. The main difficulty was to check out the version of clang and compiler-rt that would compile with a

Hello, A strange problem appears when upgrading from release_34 to testing. Some transformations to bitcode files cause registered global_ctors to not be called. Here's an example (I've also attached the complete example and pasted it below): This works: clang -fsanitize=address -flto -c -o sum.o sum.c clang -fsanitize=address -o sum sum.o This doesn't work: clang

Hello, Is this reproducible? > Fuzzing is a probabilistic business and one or even two runs don't prove > much. > I've reproduced the behavior on two different machines. Attached is a script to do so. To use the script, - create an empty folder and copy both prune-blocks.sh and ff-http-parser.sh in there - ensure clang and clang++ are in your $PATH - cd /path/to/prune-blocks.sh

On 01/21/2016 01:51 PM, Sean Silva wrote: > > > On Thu, Jan 21, 2016 at 1:33 PM, Philip Reames > <listmail at philipreames.com <mailto:listmail at philipreames.com>> wrote: > > > > On 01/19/2016 09:04 PM, Sean Silva via llvm-dev wrote: >> >> AFAIK, the cost of a well-predicted, not-taken branch is the same >> as a nop on every x86

> On Sep 21, 2016, at 9:36 AM, Kostya Serebryany via llvm-dev <llvm-dev at lists.llvm.org> wrote: > > Exciting! > > (btw, I'd prefer libfuzzer at googlegroups.com <mailto:libfuzzer at googlegroups.com> for such discussions, please start new topics there) You mean a LLVM library has a separate mailing-list? Why? — Mehdi > > I can reproduce this too, but

> your C program invokes undefined behavior when it dereferences pointers that > have been converted to other types. See for example > http://stackoverflow.com/questions/4810417/c-when-is-casting-between-pointer-types-not-undefined-behavior I don't think it's quite that simple.The type-based aliasing rules come from 6.5p7 of C11, I think. That says: "An object shall have

There is CostModel.cpp since LLVM3, I am wondering if anyone can give me an concrete example on how to use this pass to estimate cycles used in a given IR file. Thank you very much. Don

On Tue, Nov 19, 2013 at 8:25 PM, David Blaikie <dblaikie at gmail.com> wrote: > Just moving this branch of the thread out of the review because I don't > want to derail the review thread... > > Kostya - why are these two cases not optimization bugs in general? (why do > they only affect sanitizers?) > The recent case from mozilla (

Just moving this branch of the thread out of the review because I don't want to derail the review thread... Kostya - why are these two cases not optimization bugs in general? (why do they only affect sanitizers?) On Mon, Nov 18, 2013 at 8:37 PM, Kostya Serebryany <kcc at google.com> wrote: > And we've been just informed by the mozilla folks about yet another case > of

Yes, that is what I was thinking. Should I report it as a bug? On Sun, Sep 20, 2015 at 2:31 PM, Hal Finkel <hfinkel at anl.gov> wrote: > ----- Original Message ----- > > From: "Russell Wallace" <russell.wallace at gmail.com> > > To: "Hal Finkel" <hfinkel at anl.gov> > > Cc: "llvm-dev" <llvm-dev at lists.llvm.org> >

Hello all, I just noticed that LLVM has trouble recognizing nested simple select operations. My testcase is as follows: -------------------------- snip ------------------------------ #include <stdio.h> int main(int argc, char **argv) { int a; scanf("%d", &a); a = a > 255 ? 255 : a < 0 ? 0 : a; printf("A: %d\n", a); return 0; }

On Tue, Nov 19, 2013 at 8:38 AM, Kostya Serebryany <kcc at google.com> wrote: > > > > On Tue, Nov 19, 2013 at 8:25 PM, David Blaikie <dblaikie at gmail.com> wrote: > >> Just moving this branch of the thread out of the review because I don't >> want to derail the review thread... >> >> Kostya - why are these two cases not optimization bugs in

Hello, I am trying to simplify the CFG of a given code and eliminate the conditionals, even though I will obtain codes that are not semantically equivalent. For example, given a simple loop: for(i=0; i<N; i++){    a[i] = i;     if (i%2==0)       a[i] += 12; } I would keep only the loop, without the if statement: for(i=0; i<N; i++){    a[i] = i; } I can eliminate such conditionals on

Okay, as far as I can see looking through the output of that, the empty block isn't created near the end, it exists at the start and never goes away. On Sun, Sep 20, 2015 at 1:36 PM, Hal Finkel <hfinkel at anl.gov> wrote: > Hi Russell, > > Can you run your IR though opt with -O3 and -print-after-all and see when > the block becomes empty?

The root cause of those issues is the fact that sanitizers verify C++-level semantics with LLVM IR level instrumentation. For example, speculative loads are OK in IR if it can be proved that the load won't trap, but in C++ it would be a data race. On Tue, Nov 19, 2013 at 8:38 PM, Kostya Serebryany <kcc at google.com> wrote: > > > > On Tue, Nov 19, 2013 at 8:25 PM, David

Does LLVM have loop multiversioning ? it seems it does not with clang++ -O3 -mllvm -debug-pass=Arguments program.c -c bash-4.1$ clang++ -O3 -mllvm -debug-pass=Arguments fast_algorithms.c -c clang-3.6: warning: treating 'c' input as 'c++' when in C++ mode, this behavior is deprecated Pass Arguments: -datalayout -notti -basictti -x86tti -targetlibinfo -no-aa -tbaa -scoped-noalias