similar to: [LLVMdev] LLVMdev Digest, Vol 80, Issue 13

Peter Lawrence <peterl95124 at sbcglobal.net> writes: > Andrew, your response highlights a naming problem in LLVM, which is > that "array" and "vector" mean the same thing in normal computer > language and compiler theory usage, so it is inconvenient and > misleading within LLVM to give one a very specific meaning that is > different from the other.... I

Agreed, I too was wondering why we need both arrays and vectors. It goes against the grain, I think, of the structure typing system used by LLVM. For example, a vector of 4 floats and an array of 4 floats are structurally the same type. Would it be feasible in the future to consolidate the two types by allowing "vector" operations (add, multiply, etc.) on arrays where it makes

On Mon, Feb 14, 2011 at 3:49 PM, Peter Lawrence <peterl95124 at sbcglobal.net> wrote: > Andrew, >                your response highlights a naming problem in LLVM, > which is that  "array" and "vector" > mean the same thing in normal computer language and compiler theory > usage, so it is > inconvenient and misleading within LLVM to give one a very

Dave, The way I see it there should be just one pass that implements deleting UB (maybe it would come to be called UBCE), and that one pass should have a command line option simply for the reason than all passes should have one. Peter Lawrence. > On Jul 26, 2017, at 10:02 PM, David Blaikie <dblaikie at gmail.com> wrote: > > > > On Wed, Jul 26, 2017 at 9:23 PM

Mehdi, Hal’s transformation only kicks in in the *presence* of UB, and it does not matter how that UB got there, whether by function inlining or without function inlining. The problem with Hal’s argument is that the compiler does not have a built in ouija board with which it can conjure up the spirit of the author of the source code and find out if the UB was intentional with the

> > Having read all of these threads, I am thoroughly convinced by the positions put forward by others. > Chandler, others have decided to let the compiler continue mis-compiling the function-inlining example, others have decided to not fix the inability to hoist a loop invariant divide out of a loop. It sounds like you haven’t even thought about these things let alone

Dave, Dead code elimination is generally done in a pass called dead code elimination, Can you give concrete examples why the same would not be true for UB code elimination ? Yes, speculatively hoisting code requires it to be UB-free, but that has nothing to do with UBCE deleting entire blocks of code because of the existence of UB. The former requires an analysis proving UB-absense, the

> On Jul 21, 2017, at 10:55 PM, Mehdi AMINI <joker.eph at gmail.com> wrote: > > > > 2017-07-21 22:44 GMT-07:00 Peter Lawrence <peterl95124 at sbcglobal.net <mailto:peterl95124 at sbcglobal.net>>: > Mehdi, > Hal’s transformation only kicks in in the *presence* of UB > > No, sorry I entirely disagree with this assertion: I believe we

David, -fsanitize=undefined sounds great, but is not quite what I want. I recently ran into a problem with "CodeGen/MachineSink.cpp” [*], for a target that has to expand Select into control flow. The original IR had two select in a row that were based on the same condition, so the CMP that sets the FLAGS reg in the second select was MCSE’ed to the earlier CMP in the first

On Mon, Jul 31, 2017 at 7:40 AM Peter Lawrence <peterl95124 at sbcglobal.net> wrote: > Dave, > Dead code elimination is generally done in a pass called dead > code elimination, > Can you give concrete examples why the same would not be true for UB code > elimination ? > I haven't actually looked at how optimizations on the basis of the code being UB-free

Chandler, Please give some citations, I’ve search the llvm-dev archives and didn't find any. Peter Lawrence. > On Jun 28, 2017, at 12:01 PM, Chandler Carruth <chandlerc at gmail.com> wrote: > > On Wed, Jun 28, 2017 at 9:39 AM Peter Lawrence <peterl95124 at sbcglobal.net <mailto:peterl95124 at sbcglobal.net>> wrote: > > Preface: This paper

Sean, Let me re-phrase a couple words to make it perfectly clear > On Jul 21, 2017, at 6:29 PM, Peter Lawrence <peterl95124 at sbcglobal.net> wrote: > > Sean, > > Dan Gohman’s “transform” changes a loop induction variable, but does not change the CFG, > > Hal’s “transform” deletes blocks out of the CFG, fundamentally altering it. > > These are two totally

On 06/28/2017 02:18 PM, Chandler Carruth wrote: > On Wed, Jun 28, 2017 at 12:09 PM Peter Lawrence > <peterl95124 at sbcglobal.net <mailto:peterl95124 at sbcglobal.net>> wrote: > > Chandler, > Please give some citations, I’ve search the > llvm-dev archives and didn't find any. > > > They are all in the discussions from Nuno,

Andrew, This is one area of LLVM that maps very nicely to our GPU architecture. A vector is a native data type on these architectures. For example, on AMD's GPUs, the native type is 4x32bit vector with sub-components. Each of the individual 32bits can be indexed separately, but not dynamically. This is a big difference from an array of 32bit values. So there are cases where the meaning of the

Keno, Perhaps you can view the problem to be the memcpys themselves, We humans can look at the memcpys and see loads and stores but to almost all optimizer passes they aren’t what it is looking for, They instead see function calls which they mostly don’t touch, If these memcpys were inlined into plain old loads and stores The redundant loads and stores should be deleted by existing opts

Sean, Dan Gohman’s “transform” changes a loop induction variable, but does not change the CFG, Hal’s “transform” deletes blocks out of the CFG, fundamentally altering it. These are two totally different transforms. And even the analysis is different, The first is based on an *assumption* of non-UB (actually there is no analysis to perform) the second Is based on a *proof* of existence of UB

Sanjoy, The point is this, you have to take a stand one way or the other on the function-inlining issue: [1. this function *always* executes statement S, F(a) { If (a == a) S; } but in llvm if you inline it and “a” happens to be “undef” then nothing can be said about whether statement S is executed. This is indefensible.] My belief is this: that llvm exists for a

> > > Message: 5 > Date: Tue, 25 Jul 2017 00:12:35 -0700 > From: Sean Silva via llvm-dev <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> > To: Peter Lawrence <peterl95124 at sbcglobal.net <mailto:peterl95124 at sbcglobal.net>> > Cc: llvm-dev <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>>, John Regehr >

Renato, On Mar 4, 2011, at 10:00 AM, llvmdev-request at cs.uiuc.edu wrote: > That's what the packed is for. > > %Base = type { i32, i8 }; // size = 8 > %POSDerived = type { %Base, i8 }; // i8 offset = 8, size 12 > > %Basep = packed type { i32, i8 }; // size = 5 > %nonPOSDerived = type { %Basep, i8 }; // i8 offset = 5, size 8 > > cheers, > --renato does't

Peter, I strongly suggest that you take a break from this email thread and careful consider the points Chandler has made about community norms and expectations before returning to this discussion. Chandler has been exceedingly patient with explaining why your behaviour is problematic and made several concrete suggestions as to productive next steps you should take. You are actively