Stream: git-wasmtime

Topic: wasmtime / PR #2887 Implement Vpopcnt for x64

Wasmtime GitHub notifications bot (May 10 2021 at 18:11):

jlb6740 opened PR #2887 from x64_implement_packed_popcnt to main:

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Wasmtime GitHub notifications bot (May 10 2021 at 20:28):

bjorn3 submitted PR Review.

Wasmtime GitHub notifications bot (May 10 2021 at 20:28):

bjorn3 created PR Review Comment:

You can use [0x0F; 16].

Wasmtime GitHub notifications bot (May 13 2021 at 19:57):

jlb6740 updated PR #2887 from x64_implement_packed_popcnt to main.

Wasmtime GitHub notifications bot (May 13 2021 at 20:02):

jlb6740 updated PR #2887 from x64_implement_packed_popcnt to main.

Wasmtime GitHub notifications bot (May 13 2021 at 20:10):

abrown submitted PR review.

Wasmtime GitHub notifications bot (May 13 2021 at 20:10):

abrown created PR review comment:

Why don't we just use popcnt? If popcnt and vpopcnt have the same semantics then we can just use popcnt with a vector type?

Wasmtime GitHub notifications bot (May 13 2021 at 21:52):

jlb6740 submitted PR review.

Wasmtime GitHub notifications bot (May 13 2021 at 21:52):

jlb6740 created PR review comment:

It's been a while since I made that decision but it does indeed look like I've created identical lowerings. Perhaps I was duplicating an earlier effort where two instruction conversions were needed due to the input args?? Not sure. In any case, good question and I'll attempt to combine the two and hopefully it will cause not trouble. Thanks!

Wasmtime GitHub notifications bot (May 13 2021 at 21:52):

jlb6740 edited PR review comment.

Wasmtime GitHub notifications bot (May 13 2021 at 22:17):

jlb6740 created PR review comment:

Ahh .. now I see why we had to do that. It has something to do with needing to pop1_with_bitcast in the code_translator. Ultimately the verifier did not like the vector sharing the definition when compiling even though the translations in instructions.rs are identical. Perhaps you know or @cfallin knows but I remember trying this now and consciously implementing a separate translation/lowering because of an issue along these lines:

`Caused by:
0: WebAssembly failed to compile
1: Compilation error: function u0:0(i64 vmctx, i64, i8x16) -> i8x16 wasmtime_system_v {
gv0 = vmctx
gv1 = load.i64 notrap aligned readonly gv0
gv2 = load.i64 notrap aligned gv1
stack_limit = gv2

                                   block0(v0: i64, v1: i64, v2: i8x16):
   @004f                               v4 = popcnt v2
   ;~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   ; error: inst0 (v4 = popcnt.i8x16 v2): has an invalid controlling type i8x16

   @0051                               jump block1(v4)

                                   block1(v3: i8x16):
   @0051                               return v3
   }

   ; 1 verifier error detected (see above). Compilation aborted.
   ', /home/jlbirch/wasmtime_jlb6740/target/debug/build/wasmtime-cli-89f47d7a9050963a/out/wast_testsuite_tests.rs:3645:18

note: run with RUST_BACKTRACE=1 environment variable to display a backtrace`

Wasmtime GitHub notifications bot (May 13 2021 at 22:17):

jlb6740 submitted PR review.

Wasmtime GitHub notifications bot (May 13 2021 at 22:50):

abrown submitted PR review.

Wasmtime GitHub notifications bot (May 13 2021 at 22:50):

abrown created PR review comment:

That's a good find; I think the issue is that the types allowed for popcnt are too restrictive. popcnt uses the iB type, which only includes scalar integers, but I think we should make it use the Int type, which allows both scalar and vector integers.

Wasmtime GitHub notifications bot (May 13 2021 at 22:51):

abrown edited PR review comment.

Wasmtime GitHub notifications bot (May 13 2021 at 23:48):

jlb6740 submitted PR review.

Wasmtime GitHub notifications bot (May 13 2021 at 23:48):

jlb6740 created PR review comment:

Ok .. Yes, makes sense. Do we want to just merged this here and refactor that in a separate patch or do it here?? My only thought is fixing a patch that currently works (should work) .. creating some unintended consequence not realizing the restriction to 1b was there for some non-obvious reason. In any case I do suddenly have failures below to check on so I'll fix that first. Will likely continue to be very slow to respond to updates this coming week unfortunately but will get back to normal soon.

Wasmtime GitHub notifications bot (May 13 2021 at 23:48):

jlb6740 edited PR review comment.

Wasmtime GitHub notifications bot (May 14 2021 at 00:06):

cfallin submitted PR review.

Wasmtime GitHub notifications bot (May 14 2021 at 00:06):

cfallin created PR review comment:

I think it's probably better to avoid adding vpopcnt in the first place rather than cleaning up in a subsequent PR -- hopefully the changes are minor on the lowering side (basically it should be just a conditional in the Opcode::Popcnt case, on the type, like the arithmetic operators have). Thanks!

Wasmtime GitHub notifications bot (May 21 2021 at 03:46):

jlb6740 updated PR #2887 from x64_implement_packed_popcnt to main.

Wasmtime GitHub notifications bot (May 21 2021 at 04:17):

jlb6740 updated PR #2887 from x64_implement_packed_popcnt to main.

Wasmtime GitHub notifications bot (May 21 2021 at 17:13):

abrown created PR review comment:

            let ty = ty.unwrap();
            if !ty.is_vector() {

Wasmtime GitHub notifications bot (May 21 2021 at 17:13):

abrown submitted PR review.

Wasmtime GitHub notifications bot (May 21 2021 at 17:14):

abrown submitted PR review.

Wasmtime GitHub notifications bot (May 21 2021 at 17:14):

abrown created PR review comment:

Rename ty to input_ty? Or is this necessary?

Wasmtime GitHub notifications bot (May 21 2021 at 17:17):

abrown submitted PR review.

Wasmtime GitHub notifications bot (May 21 2021 at 17:17):

abrown created PR review comment:

@bnjbvr, what does ty mean here?

Wasmtime GitHub notifications bot (May 21 2021 at 17:20):

abrown submitted PR review.

Wasmtime GitHub notifications bot (May 21 2021 at 17:23):

abrown edited PR review comment.

Wasmtime GitHub notifications bot (May 21 2021 at 17:23):

abrown deleted PR review comment.

Wasmtime GitHub notifications bot (May 21 2021 at 17:23):

abrown submitted PR review.

Wasmtime GitHub notifications bot (May 21 2021 at 17:25):

jlb6740 updated PR #2887 from x64_implement_packed_popcnt to main.

Wasmtime GitHub notifications bot (May 21 2021 at 21:53):

jlb6740 updated PR #2887 from x64_implement_packed_popcnt to main.

Wasmtime GitHub notifications bot (May 22 2021 at 02:23):

jlb6740 merged PR #2887.

Wasmtime GitHub notifications bot (May 24 2021 at 08:02):

bnjbvr submitted PR review.

Wasmtime GitHub notifications bot (May 24 2021 at 08:02):

bnjbvr created PR review comment:

Yeah, it was something along those lines, from peaking at the previous version of this source code, when the input type is narrower than 32-bits, we'd just do the 32-bits version of the instruction, zero-extending the input prior to this.

Last updated: Oct 23 2024 at 20:03 UTC