I'd like to replace scalar instructions with vector instructions such
that the code corresponding to following tree would be vectorized:
load0 load1
\ /
\ /
add/sub/mul
|
|
store
I had unsuccessful encounters with load0->replaceAllUsesWith(vec_load0)
complaining about mismatching type (makes sense, add's other operand is
still scalar at that time..)
Is the only way to create a vectorized version of this tree by
1) creating the vector loads vec_load0 AND vec_load1
2) retrieving the opcode of the arithmetic instruction and create a new
one according to the opcode
How is step 2) in donepractice? Cloning the instruction and replacing
the operands? (would that bypass the type checking for a moment?)
Thanks,
Frank
Hi Frank, SLP vectorizer does something like this. For question (2) you could take a glance at BoUpSLP::vectorizeTree(TreeEntry *E) (file lib/Transforms/Vectorize/SLPVectorizer.cpp) - it also has an example of retrieving an instruction’s opcode and constructing vector operands. Michael> On Jul 8, 2015, at 3:18 PM, Frank Winter <fwinter at jlab.org> wrote: > > I'd like to replace scalar instructions with vector instructions such that the code corresponding to following tree would be vectorized: > > load0 load1 > \ / > \ / > add/sub/mul > | > | > store > > I had unsuccessful encounters with load0->replaceAllUsesWith(vec_load0) complaining about mismatching type (makes sense, add's other operand is still scalar at that time..) > > Is the only way to create a vectorized version of this tree by > > 1) creating the vector loads vec_load0 AND vec_load1 > 2) retrieving the opcode of the arithmetic instruction and create a new one according to the opcode > > How is step 2) in donepractice? Cloning the instruction and replacing the operands? (would that bypass the type checking for a moment?) > > Thanks, > Frank > > _______________________________________________ > LLVM Developers mailing list > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20150708/d93a6c83/attachment.html>
Hi Frank,
I’m assuming you are widening the loads for you vectorization, so what I would
do is something like that:
Step #1: Widen the load and extract:
vec_load0 load1
| |
extract_element /
\ /
\ /
add/sub/mul
|
|
store
Step #2: Do the same for the second load.
vec_load0 vec_load1
| |
extract_element extract_element
\ /
\ /
add/sub/mul
|
|
store
Step #3: Promote the arithmetic operation to a vector one (mutate type).
vec_load0 vec_load1
\ /
\ /
vec_add/sub/mul
|
extract_element
|
store
Step #4: Promote the store and get rid of the extract.
vec_load0 vec_load1
\ /
\ /
vec_add/sub/mul
|
|
vec_store
Note: There is a class to help promoting scalar operation to vector operation in
codegen prepare. It was designed to reusable, so check it out and see it helps
we could move its implementation elsewhere.
> On Jul 8, 2015, at 3:18 PM, Frank Winter <fwinter at jlab.org> wrote:
>
> I'd like to replace scalar instructions with vector instructions such
that the code corresponding to following tree would be vectorized:
>
> load0 load1
> \ /
> \ /
> add/sub/mul
> |
> |
> store
>
> I had unsuccessful encounters with load0->replaceAllUsesWith(vec_load0)
complaining about mismatching type (makes sense, add's other operand is
still scalar at that time..)
>
> Is the only way to create a vectorized version of this tree by
>
> 1) creating the vector loads vec_load0 AND vec_load1
> 2) retrieving the opcode of the arithmetic instruction and create a new one
according to the opcode
>
> How is step 2) in done practice?
What we did in codegen prepare is that we create a new operation (e.g.,
extract_element undef), that we use to replace all the users of the initial
operation, then we mutate the type of the initial operation, and that use it in
the new operation (e.g., extract_element undef becomes extract_element vec_op).
Cheers,
-Quentin
> Cloning the instruction and replacing the operands? (would that bypass the
type checking for a moment?)
>
> Thanks,
> Frank
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
Two ways I've done this: 1. Create a ReplaceAllUsesWithUnsafe() function that does the same as ReplaceAllUsesWith except without the check for compatible types, knowing that eventually you will end up with a fully compatible instruction eventually. 2. Do a recursive traversal up the use-def chain from the store back through all the args. This will ensure that at every instruction, all the args will have been vectorized through the recursion, and all you really need to do at that point is call Instruction::mutateType() to ensure the return type of the instruction matches the vector args. Thanks Jason On Wed, Jul 8, 2015 at 3:18 PM, Frank Winter <fwinter at jlab.org> wrote:> I'd like to replace scalar instructions with vector instructions such that > the code corresponding to following tree would be vectorized: > > load0 load1 > \ / > \ / > add/sub/mul > | > | > store > > I had unsuccessful encounters with load0->replaceAllUsesWith(vec_load0) > complaining about mismatching type (makes sense, add's other operand is > still scalar at that time..) > > Is the only way to create a vectorized version of this tree by > > 1) creating the vector loads vec_load0 AND vec_load1 > 2) retrieving the opcode of the arithmetic instruction and create a new > one according to the opcode > > How is step 2) in donepractice? Cloning the instruction and replacing the > operands? (would that bypass the type checking for a moment?) > > Thanks, > Frank > > _______________________________________________ > LLVM Developers mailing list > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20150708/4b747382/attachment.html>