similar to: Comparing stack addresses and function args (Was: [llvm] r174131 - Add a comment explaining an unavailable optimization)

On Thu, Sep 24, 2015 at 12:06 PM, Aaron Ballman <aaron at aaronballman.com> wrote: > On Thu, Sep 24, 2015 at 2:42 PM, Hans Wennborg <hans at chromium.org> wrote: >> I was wondering why LLVM cannot optimize this code (which GCC does optimize): >> >> int f(int *p) { int x; return p == &x; } >> >> it would seem that this must always return 0. (This

I threw together a patch which implements this (attached.) If we decide that this is actually a legal transform, I'm happy to post this for review. In addition to the version proposed here, I also implemented a case where a trivially escaped alloca's address is not equal to any other value. I believe both are valid, but we should confirm. Philip On 09/24/2015 02:34 PM, Aaron

On 09/24/2015 06:04 PM, Hans Wennborg wrote: > I tried your patch on a Clang build to see if it would fire. It > reduced the size of a bootstrap with 8500 bytes. Not huge, but it > seems like a nice improvement. And maybe it could be made more > powerful: not just checking if the address is a param or alloca, but > an address based on such values. Yeah, I realized after posting that

Hi folks, I'm hitting the below assertion failure when compiling this small piece of C code (repro.c, attached). My command line is: bin/clang --target=aarch64-linux-gnu -c -O2 repro.c clang is built from top of trunk as of this morning. It only happens at -O2, and it doesn't happen with the default target (x86_64). I tried to reproduce using just 'llc -O2' but didn't

Sure. David, what do you think about merging this to 3.9? Sanjay: are you saying I'd just apply that diff to InstructionSimplify.cpp, not InstCombineSelect.cpp? On Fri, Jul 22, 2016 at 7:08 AM, Sanjay Patel <spatel at rotateright.com> wrote: > Hi Hans - > > Yes, I think this is a good patch for 3.9 (cc'ing David Majnemer as code > owner). The functional change was

Thanks for notifying me. Yes, this was a recent change. Taking a look now. On Wed, Jul 20, 2016 at 1:49 PM, Michael Kuperstein <mkuper at google.com> wrote: > +Sanjay, who touched this last. :-) > > On Wed, Jul 20, 2016 at 12:44 PM, Ismail Badawi (ibadawi) via llvm-dev < > llvm-dev at lists.llvm.org> wrote: > >> Hi folks, >> >> I'm hitting the

David, Sanjay: ping? On Mon, Jul 25, 2016 at 11:07 AM, Hans Wennborg <hans at chromium.org> wrote: > Sure. David, what do you think about merging this to 3.9? > > Sanjay: are you saying I'd just apply that diff to > InstructionSimplify.cpp, not InstCombineSelect.cpp? > > On Fri, Jul 22, 2016 at 7:08 AM, Sanjay Patel <spatel at rotateright.com> wrote: >> Hi

LGTM On Wednesday, July 27, 2016, Hans Wennborg <hans at chromium.org> wrote: > David, Sanjay: ping? > > On Mon, Jul 25, 2016 at 11:07 AM, Hans Wennborg <hans at chromium.org > <javascript:;>> wrote: > > Sure. David, what do you think about merging this to 3.9? > > > > Sanjay: are you saying I'd just apply that diff to > >

Sanjay: let me know if this is something that will apply to 3.9. Thanks, Hans On Wed, Jul 20, 2016 at 5:59 PM, Sanjay Patel via llvm-dev <llvm-dev at lists.llvm.org> wrote: > Quick update - the bug existed before I refactored that chunk in > InstSimplify with: > https://reviews.llvm.org/rL275911 > > In fact, as discussed in https://reviews.llvm.org/D22537 - because we have a

<cc'ing llvmdev> On Nov 10, 2010, at 6:38 AM, Duncan Sands wrote: > Hi Chris, in commit 12800 you introduced the following transform: > > Implement select.ll:test12* > > This transforms code like this: > > %C = or %A, %B > %D = select %cond, %C, %A > into: > %C = select %cond, %B, 0 > %D = or %A, %C > > Since B is often a

Dear all, If possible, I would like to contribute to LLVM. First of all, I would like to say that I'm a newbie in LLVM, and my experience in compilers implementation is only in simples and academics "toy projects". My main interesting are focused in try to improve the code generated by LLVM, where "improve" I mean "better performance". I'm interested, for

As Sanjay noted in D31426<https://reviews.llvm.org/D31426#712701>, InstructionSimplify is missing the following simplification: This function: define <4 x i32> @splat_operand(<4 x i32> %x) { %splat = shufflevector <4 x i32> %x, <4 x i32> undef, <4 x i32> zeroinitializer %shuf = shufflevector <4 x i32> %splat, <4 x i32> undef, <4 x i32>

Hi Duncan, Thank you a lot for your time to provide that great and informative explanation. Now the "undef" logic makes much more sense for me. >> /You are wrong to say that "div undef, %X" is folded to "undef" by InstructionSimplify, it is folded to zero./ My mistake. I meant to say "*f****div* undef, %X" is folded to "undef" (not

Duncan, > Hi Oleg, > >> >> /This is either a mistake, or a decision that in LLVM IR snans >> are always >> considered to be signalling. / >> Yes, this seems to be an agreement to treat "undef" as a SNaN for >> "fdiv". > > "undef" is whatever bit pattern you want it to be, i.e. the compiler > can assume it is any

Hi, This is regarding a TODO mentioned in getIdentityValue function in InstructionCombining.cpp file. //TODO: We can handle other cases e.g. Instruction::And, Instruction::Or etc. I wanted to know what could be the use cases of implementing these. When I tried implementing these and wrote test cases for the same, the test cases would be optimized in InstructionSimplify before hitting the code

On Wed, Dec 12, 2012 at 01:59:55PM -0800, Dan Gohman wrote: > The bug here isn't in clang's use of noalias or in BasicAliasAnalysis' > implementation of noalias; it's in the code that's optimizing the > icmp. Let's come back to this. The attached patch decouples InstSimplify from the alias analysis and provides the conservative logic for when pointers are not

I'm looking for some opportunities to contribute to the LLVM core without too big of a learning curve. The open projects page<http://llvm.org/OpenProjects.html#misc_imp>suggests moving logic from the instruction combining transformation to the InstructionSimplify analysis. But it looks like some work has been done there since the projects page was last edited. Is there more benefit to

Hi, There are cases where LLVM is able to detect some UB but clang is not. For example, unsigned int foo(unsigned int x) { int ret = 0; for(int i = 0; i <= 32; ++i) ret += x >> i; return ret; } When the loop is unrolled, LLVM InstructionSimplify will catch it and return a UNDEF value. How can we let LLVM report some warning message to help developers correct the error?

Hi Duncan, Thank you for your comment to the bug 16257. I am new to LLVM, so not all the aspects of LLVM's /"undef"/ seem clear to me yet. I read and understood the examples from the LLVM documentation: http://llvm.org/docs/LangRef.html#undefined-values However, those examples do not cover all of the possible contexts where /"undef"/ can appear. E.g., I can't

On Fri, Nov 13, 2020 at 3:01 PM Florian Hahn <florian_hahn at apple.com> wrote: > > > > On Nov 12, 2020, at 21:36, Cameron McInally <cameron.mcinally at nyu.edu> wrote: > > On Thu, Nov 12, 2020 at 2:47 PM Florian Hahn <florian_hahn at apple.com> wrote: > > There certainly is some pieces around the edges that will need adjusting or become obsolete, but I