similar to: What can the optimizer assume about the memory a global function pointer points to?

Hello everyone, This week I was looking into the following example ( https://godbolt.org/z/uhgQcq) where two constants are written to a local array and an input argument, masked and shifted, is used to select between them. The possible values for the CC variable are 0 and 1, so I'm expecting that at the maximum level of optimizations the two constants are actually propagated, resulting in the

Hi, We are developing a bounded model checker for C/C++ programs (http://baldur.iti.kit.edu/llbmc/) that operates on LLVM's intermediate representation. While checking a C++ program that uses STL containers we noticed that llvm-gcc and clang handle pointer differences in disagreeing ways. Consider the following C function: int f(int *p, int *q) { return q - p; } Here's the

Hi All, I was wondering if there is an optimisation pass that moves a stack allocated array, initialised with constant values, to a global constant array. And if there is such a pass, what requirements are there for it to operate? My optimised IR is below. As you can see an array of 5 integers is created with alloca, then each element is stored to in turn. It would be nice if this array was

Hi Stephan, > We are developing a bounded model checker for C/C++ programs > (http://baldur.iti.kit.edu/llbmc/) that operates on LLVM's intermediate > representation. While checking a C++ program that uses STL containers > we noticed that llvm-gcc and clang handle pointer differences in > disagreeing ways. > > Consider the following C function: > int f(int *p, int *q)

I'm hitting a strange pointer aliasing "bug". Here is a test case : /* SOURCE CODE */ #define little_list_size 8 class LittleList1 { public: int _length; double _data[ little_list_size ]; LittleList1( int length ) { _length = length; for( int i=0; i<length; i++ ) _data[i] = 0; } }; class LittleList2 { public: int _length; double _data[ little_list_size ];

Hi Dan and Others , I'm newbie to LLVM and Clang ,But has experience on compiler optimization and VM . Everyone talking about the LLVM in my organisation so thought of peeking into it and where this discussion is stalled me ... so i tried to simulate the problem ,which is discussed here . vi sample.c double f(double** p ) { double a,b,c; double * x = &a; double * y =

On 23 May 2014 09:42, Robert Lougher <rob.lougher at gmail.com> wrote: > Hi Nick, > > Thanks for replying. Bug filed: > http://llvm.org/bugs/show_bug.cgi?id=19842 Thank you! Strangely enough, my first conclusion was that %p was being marked > readnone incorrectly as it wasn't handling the copy via @get_addr. > Sorry -- saying %p alone is ambiguous because

Confirmed, this is a bug. This define i32* @get_pntr(i32* %p) nounwind uwtable { entry: ret i32* %p } define void @store(i32* %p) noinline nounwind uwtable { entry: %call = call i32* @get_pntr(i32* %p) store i32 10, i32* %call, align 4 ret void } run through opt -functionattrs gets a 'readnone' on @store's %p. That's wrong, it clearly stores to it. The bug is due to

On 05/21/2014 02:52 PM, Robert Lougher wrote: > On 21 May 2014 21:40, Robert Lougher <rob.lougher at gmail.com> wrote: >> define i32* @get_pntr(i32* readnone %p) { >> entry: >> ret i32* %p >> } >> >> define void @store(i32* nocapture readnone %p) { >> entry: >> store i32 10, i32* %p, align 4, !tbaa !1 >> ret void >> }

Hi, I'm investigating a bug which I have so far been able to narrow down to the following small testcase: ======== test.c =========== int *get_pntr(int *p) { return p; } __attribute__((noinline)) void store(int *p) { int *p2 = get_pntr(p); *p2 = 10; } int test() { int i; store(&i); return i; } ----------------------------- If this is compiled in two steps as

On 01/05/2017 10:55 AM, Sanjoy Das wrote: > Hi Hal, > > On Thu, Jan 5, 2017 at 6:12 AM, Hal Finkel <hfinkel at anl.gov> wrote: >> On 01/04/2017 10:35 PM, Sanjoy Das via llvm-dev wrote: >>> I just realized that there's an annoying corner case to this scheme -- >>> I can't DSE stores across readnone maythrow function calls because the >>>

On 01/05/2017 12:17 PM, Reid Kleckner wrote: > On Thu, Jan 5, 2017 at 9:19 AM, Hal Finkel via llvm-dev > <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote: > > > On 01/05/2017 10:55 AM, Sanjoy Das wrote: > > Hi Hal, > > On Thu, Jan 5, 2017 at 6:12 AM, Hal Finkel <hfinkel at anl.gov > <mailto:hfinkel

Nyx wrote: > Hello, > > I'm in a situation where my code is calling many native functions. > Sometimes, these calls are simply calls to static "accessor" methods that > read a variable in some class object (object pointer as input, member > variable value returned as output). I was wondering if using the > setOnlyReadsMemory method on the native function objects

Hi John, > Are functions marked as readnone or readonly in the LLVM IR allowed to > generate output or to exhibit exceptional behavior (e.g., calling > abort(), generating an MMU fault, etc.)? they are allowed to unwind exceptions for example, since in theory this can occur without scrunching externally visible memory (for example unwinding can be done by having functions return an

On 01/05/2017 12:45 PM, Mehdi Amini wrote: > >> On Jan 5, 2017, at 10:39 AM, Hal Finkel via llvm-dev >> <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote: >> >> >> On 01/05/2017 12:17 PM, Reid Kleckner wrote: >>> On Thu, Jan 5, 2017 at 9:19 AM, Hal Finkel via llvm-dev >>> <llvm-dev at lists.llvm.org

On 6/21/12 2:23 AM, Duncan Sands wrote: > Hi John, > >> Are functions marked as readnone or readonly in the LLVM IR allowed to >> generate output or to exhibit exceptional behavior (e.g., calling >> abort(), generating an MMU fault, etc.)? > they are allowed to unwind exceptions for example, since in theory this > can occur without scrunching externally visible memory

LLVM today does not clearly specify if a function specified to not write to memory (i.e. readonly or readnone) is allowed to throw exceptions. LangRef is ambiguous on this issue. The normative statement is "[readnone/readonly functions] cannot unwind exceptions by calling the C++ exception throwing methods" which does not decide an answer for non C++ languages. It used to say (h/t

No concerns from me. I use Alive2 all the time, and it would be fantastic to have it available online reliably. If we can get Alive1 up there too, that would be even better. I still use that to try to prove things where it's not obvious how to express the relationships in pure LLVM IR: https://rise4fun.com/Alive/NDu On Wed, Jun 17, 2020 at 4:05 PM Chris Lattner via llvm-dev < llvm-dev at

>but is there or is there not accessible, visible state, Wouldn't ReadNone and/or ReadOnly cover that? If ReadNone is set, it means it doesn't access any of the visible (accessible) states. - Vaivaswatha On Fri, Dec 4, 2015 at 3:17 PM, James Molloy <james at jamesmolloy.co.uk> wrote: > Hi, > > I don't think the attribute as is is strong enough to do what you

Hi Ralf On Wednesday, June 1, 2011, Ralf Karrenberg <Chareos at gmx.de> wrote: > Hi, > > The last time the AVX backend was mentioned on this list seems to be > from November 2010, so I would like to ask about the current status. Is > anybody (e.g. at Cray?) still actively working on it? I don't think so! > I have tried both LLVM 2.9 final and the latest trunk, and it