search for: vectorizable

...compiled the simple program: > > #include <stdio.h> > #include <stdlib.h> > > int v1[10000]; > > int main() > { > int i; > > for (i = 0; i < 10000; i++) { > v1[i] = i; > } > > This loop is not really vectorizable, even if LLVM had an auto-vectorizer. You need the same operation (floating-point or integer) applied to contiguous elements in a vector. An example of a vectorizable loop body would be "v1[i] = v1[i] * v1[i]" Then, you could use SSE (or any other vector instruction set) to get a subst...

...> > I.e., do you mean for real vector machines, a la Cray, or for > > the packed media instructions that are currently so popular? > > I am mostly interested in generating code for the popular SIMD cpus > (X86, ARM, PPC, etc). > > > What's your idea for finding vectorizable loops? > > I started with a very very basic check because I needed to start > somewhere. We will need to design a mode advanced check. > > > Do you have a plan for xforms to increase the amount of > > vectorization? > > Yes. We will need to implement a predication p...

...rward. I'd start by making a plan (a design!) with goals and stuff. Publish it so we can see what you mean by "vectorization". I.e., do you mean for real vector machines, a la Cray, or for the packed media instructions that are currently so popular? What's your idea for finding vectorizable loops? Do you have a plan for xforms to increase the amount of vectorization? What books, papers, theses are you looking at (so we can get on the same page)? I've written a dependence analyzer that ought to be suitable (if it isn't, we should fix it). Thanks, Preston

...be able to generate code for them. > I.e., do you mean for real vector machines, a la Cray, or for > the packed media instructions that are currently so popular? I am mostly interested in generating code for the popular SIMD cpus (X86, ARM, PPC, etc). > What's your idea for finding vectorizable loops? I started with a very very basic check because I needed to start somewhere. We will need to design a mode advanced check. > Do you have a plan for xforms to increase the amount of vectorization? Yes. We will need to implement a predication phase and to design the interaction with oth...

Hi Gerolf, I think we have several (perhaps separable) issues here: 1. Do we have a canonical form for loops, preserved through the optimizer, that allows naturally-constructed loop nests to remain separable? 2. Do we forbid non-lowering transformations that turn vectorizable loops into non-vectorizable loops? 3. How do we detect cases where transformations cause a negative answer to either of the above? Now (2) is a subset of (1), but (1) applies as a general structural property to a much larger class of transformations. Hyojin has found, and proposed a fix for, two...

Hello. I have compiled the simple program: #include <stdio.h> #include <stdlib.h> int v1[10000]; int main() { int i; for (i = 0; i < 10000; i++) { v1[i] = i; } for (i = 0; i < 10000; i++) { printf("%d ", v1[i]); } return 0; } Next, I disasseble the executable file and have not found

...not introduce redundant checks in the first place (although it would imply some gymnastics when examining the control flow around the loop and then restructuring things when we generate the code for the loop). The scalar remainder loop, when reached from the vectorized loop, is already known to be vectorizable to a VF larger than EpilogVF. No need to introduce again any potential aliasing, wrapping or whatnot checks, even if this redundancy can later be eliminated, if instead this vectorizability property could be recorded somehow. Similar to having annotated the remainder loop with “#pragma clang loop v...

...> > I.e., do you mean for real vector machines, a la Cray, or for > > the packed media instructions that are currently so popular? > > I am mostly interested in generating code for the popular SIMD cpus > (X86, ARM, PPC, etc). > > > What's your idea for finding vectorizable loops? > > I started with a very very basic check because I needed to start > somewhere. We will need to design a mode advanced check. > > > Do you have a plan for xforms to increase the amount of > > vectorization? > > Yes. We will need to implement a predication p...

...instruction vectorization. To give you a broad idea, this includes information like: - uniform/varying operation - same/consecutive/random index vector (for load/store) - aligned/unaligned index vector (for load/store) - operations that can not be vectorized (marked as "split", e.g. non-vectorizable types etc.) - operations that need to be split and guarded (e.g. unknown calls, stores) - mandatory/optional blocks (renamed from "divergent"/"non-divergent" in [2]) - divergent/non-divergent loops Generally, it would be possible to implement a loop vectorizer on top of WFV s...

...ke Tierney <luke@stat.uiowa.edu> writes: > > > >> Vectorized operations in R are also as fast as compiled C (because > >> that is what they are :-)). A compiler such as the one > I'm working > >> on will be able to make most difference for > non-vectorizable or not > >> very vectorizable code. It may also be able to reduce the > need for > >> intermediate allocations in vectorizable code, which may > have other > >> benefits beyond just speed improvements. > > > > Actually, it has struck me a couple of...

...ure > if it can help that much. Renato, I prefer not to estimate the encoding > size of instructions. We know that vector instructions take more space to > encode. Will knowing the exact number help us in making a better decision ? > I don’t think so. On modern processors when running vectorizable loops, the > code size of the vector instructions is almost never the bottleneck. You're talking about -Os, where the user has explicitly asked the compiler to optimize the code size. Saying that the code size isn't a speed bottleneck seems to miss the point. > > On Jun 5, 2013,...

...zero, so I am not sure if it can help that much. Renato, I prefer not to estimate the encoding size of instructions. We know that vector instructions take more space to encode. Will knowing the exact number help us in making a better decision ? I don’t think so. On modern processors when running vectorizable loops, the code size of the vector instructions is almost never the bottleneck. Thanks, Nadav On Jun 5, 2013, at 6:09 AM, David Tweed <david.tweed at arm.com> wrote: > On 5 June 2013 13:32, David Tweed <david.tweed at arm.com> wrote: > This is what I'd like to know about:...

...memchecks required for each: 1. Loop Vectorizer: each memory access is checked against all other memory accesses in the loop (except read vs read) 2. Loop Distribution: only memory accesses in different partitions are checked against each other. The loop vectorizer will add its own checks for the vectorizable distributed loops 3. Loop Fusion: accesses from the to-be-merged loops should be checked against each other 4. LICM: if hoisting a load, stores needs to be check. When sinking a store, all accesses are checked 5. Load-elimination in GVN: all *intervening* stores need to be checked. 6. Instruction...

...ding on that choice.  It does hint at a possible direction for implementation though, and implies that most of the cost modeling pieces are already in place. The use cases I'm looking at basically fall into two buckets: for (int i = 0; i < N; i++) {   if (expr(a[i])) break;   ... other vectorizable stuff ... } for (int i = 0; i < N; i++) {   if (expr(i)) break;   ... other vectorizable stuff ... } The former are the actually "interesting" examples.  The later are cases where we missed eliminating some check we could have, but not-vectorizing creates an unfortunate performan...

....h> >> #include <stdlib.h> >> >> int v1[10000]; >> >> int main() >> { >> int i; >> >> for (i = 0; i < 10000; i++) { >> v1[i] = i; >> } >> >> > This loop is not really vectorizable, even if LLVM had an auto-vectorizer. > You need the same operation (floating-point or integer) applied to > contiguous elements in a vector. An example of a vectorizable loop body > would be "v1[i] = v1[i] * v1[i]" Then, you could use SSE (or any other > vector instruction...

...-line flag or a loop hint. - Explore and fine-tune the proper cost model for loop distribution to allow partial vectorization. This is essentially whether to partition and what these partitions should be. Currently instructions are mapped to partitions using a simple heuristics to create a vectorizable partitions. We may need to interact with the vectorizer to make sure the vectorization will actually happen and it will be overall profitable. - Explore other potentials for loop distribution, e.g.: - Partial vectorization of loops that can't be if-converted - Classic loop distributio...

...vectorizing with -O3, but still a good number of programs. At the same time the code growth is minimal. Most workloads are unaffected and the total code growth for the entire test suite is 0.89%. Almost all of the code growth comes from the TSVC test suite which contains a large number of large vectorizable loops. I did not measure the compile time in this batch but I expect to see an increase in compile time in vectorizable loops because of the time we spend in codegen. I am interested in hearing more opinions and discussing more measurements by other people. Nadav . -------------- next part -...

...d by 100. > But the loop takes about 10 minutes, the vectorized > operation takes about 3 > seconds. (See below) > Why that? Shouldn?t the loop take max 100*3seconds = 5 minutes? > > I?m interested in that because I think that I will have > computations that > are easily vectorizable(like this example) and that I will > have computations > that are not/very difficult vectorizable. > > Marcus Jellinghaus > > > > print(dim(test)[1]) > [1] 500000 > > Sys.time() > [1] "2002-10-07 06:17:33 Eastern Sommerzeit" > > test[1:100,6]...

...e the LLVM loop > > > > > > vectorizer > > > > > > fails the test whether the loop latch and exiting block of > > > > > > a > > > > > > loop > > > > > > is > > > > > > the same. The loops are vectorizable, and get vectorized > > > > > > with > > > > > > LLVM > > > > > > -O2 > > > > > > > > > > > > > > > > > > > > I would be interested to know why -O2 succeeds here. > > > &g...

...gt;>> > >>>> Vectorized operations in R are also as fast as compiled > C (because > >>>> that is what they are :-)). A compiler such as the one > >> I'm working > >>>> on will be able to make most difference for > >> non-vectorizable or not > >>>> very vectorizable code. It may also be able to reduce the > >> need for > >>>> intermediate allocations in vectorizable code, which may > >> have other > >>>> benefits beyond just speed improvements. > >>> &gt...