WebAssembly / WebAssembly/binaryen

Cannot optimize complex ge_u 0 out

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#7,556 0 comments 0 reactions 0 assignees View on GitHub

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WebAssembly
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Description

Given the following code:

(module
  (type $0 (func))
  (type $1 (func (param i32 i32) (result i32)))
  (type $2 (func (result i32)))
  (type $3 (func (param i32) (result i32)))
  (import "External" "external_function" (func $external_function (type $0)))
  (func $_start (type $3) (param $0 i32) (result i32)
    (local $1 i32) (local $2 i32)
    i32.const 0
    i32.load
    local.set $2
    local.get $1
    i32.const 0
    call $foo
    local.set $1
    local.get $1
    local.get $2
    i32.le_u
    if (result i32)
      i32.const 0
    else
      call $external_function
      i32.const 1
    end)
  (func $foo (type $1) (param $0 i32) (param $1 i32) (result i32)
    i32.const 0
    i32.const 0
    i32.store
    i32.const 0)
  (memory $0 258 258)
  (export "_start" (func $_start)))

wasm-opt (e6d02fa1) -all -O3 cannot optimize the

   (i32.ge_u
    (i32.load
     (i32.const 0)
    )
    (block (result i32)
     (i32.store
      (i32.const 0)
      (i32.const 0)
     )
     (i32.const 0)
    )
   )

to one (while -all -O2 can)

It is already discussed in #7455 (complex lt_u 0). in contrast, this is complex ge_u 0. So fix this the way as before.

Contributor guide

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the supplied wasm-opt e6d02fa1 example and compare the -all -O2 and -all -O3 results. Read issue #7455 and its implementation or tests for complex lt_u 0, then verify that the equivalent complex ge_u 0 pattern is reduced to one under -O3.

Written by the indexing model from the issue text.

Assessment

Tech stack
wasm
Domain
compilers
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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