Bug 1707774 Comment 13 Edit History

Note: The actual edited comment in the bug view page will always show the original commenter’s name and original timestamp.

Original comment by
on 
Getting rid of loop by using v2 more:
```
new WebAssembly.Module(wasmTextToBinary(`
(module
  (func (result i64)
    (local $n i64)                ;; zero
    (if (global.get $flag)        ;; give $flag high priority;
        (return (i64.const 7)))   ;;  do not touch $n
    (if (global.get $flag)
        (return (i64.const 8)))
    (if (global.get $flag)
        (return (i64.const 9)))
    (if (global.get $flag)
        (return (i64.const 10)))
    (if (global.get $flag)
        (return (i64.const 11)))
    (if (global.get $flag)
        (return (i64.const 12)))
    (local.set $n                 ;; $n = zero, but this is
      (i64.mul (local.get $n)     ;;  not known because i64.mul
               (local.get $n)))   ;;   is not constant folded
    (if (global.get $flag)        ;; conditionally
        (return (local.get $n)))  ;;  read $n
    (global.set $flag             ;; introduce
      (i32.const 1))              ;;  global effect
    (i64.load (i32.const 48))     ;; maybe traps
    drop                          ;;  but ignore result
    (local.get $n))               ;; read $n
  (memory 1)
  (global $flag (mut i32) (i32.const 2)))
`))
```
Revision 1 by
on 
Getting rid of loop by using v2 more, and get rid of the setting of $flag
```
new WebAssembly.Module(wasmTextToBinary(`
(module
  (func (result i64)
    (local $n i64)                ;; zero
    (if (global.get $flag)        ;; give $flag high priority;
        (return (i64.const 7)))   ;;  do not touch $n
    (if (global.get $flag)
        (return (i64.const 8)))
    (if (global.get $flag)
        (return (i64.const 9)))
    (if (global.get $flag)
        (return (i64.const 10)))
    (if (global.get $flag)
        (return (i64.const 11)))
    (if (global.get $flag)
        (return (i64.const 12)))
    (local.set $n                 ;; $n = zero, but this is
      (i64.mul (local.get $n)     ;;  not known because i64.mul
               (local.get $n)))   ;;   is not constant folded
    (if (global.get $flag)        ;; conditionally
        (return (local.get $n)))  ;;  read $n
    (i64.load (i32.const 48))     ;; maybe traps
    drop                          ;;  but ignore result
    (local.get $n))               ;; read $n
  (memory 1)
  (global $flag (mut i32) (i32.const 2)))
`))
```
Revision 2 by
on 
Getting rid of loop by using v2 more, and get rid of the setting of $flag.  I'm starting to suspect that the effect of the load is simply to make x0 be allocated to something other than $n so that there can be some turbulence in the function tail.
```
new WebAssembly.Module(wasmTextToBinary(`
(module
  (func (result i64)
    (local $n i64)                ;; zero
    (if (global.get $flag)        ;; give $flag high priority;
        (return (i64.const 7)))   ;;  do not touch $n
    (if (global.get $flag)
        (return (i64.const 8)))
    (if (global.get $flag)
        (return (i64.const 9)))
    (if (global.get $flag)
        (return (i64.const 10)))
    (if (global.get $flag)
        (return (i64.const 11)))
    (if (global.get $flag)
        (return (i64.const 12)))
    (local.set $n                 ;; $n = zero, but this is
      (i64.mul (local.get $n)     ;;  not known because i64.mul
               (local.get $n)))   ;;   is not constant folded
    (if (global.get $flag)        ;; conditionally
        (return (local.get $n)))  ;;  read $n
    (i64.load (i32.const 48))     ;; maybe traps
    drop                          ;;  but ignore result
    (local.get $n))               ;; read $n
  (memory 1)
  (global $flag (mut i32) (i32.const 2)))
`))
```
Revision 3 by
on 
Getting rid of loop by using v2 more, and get rid of the setting of $flag.  I'm starting to suspect that the effect of the load is simply to make x0 be allocated to something other than $n in the function tail.
```
new WebAssembly.Module(wasmTextToBinary(`
(module
  (func (result i64)
    (local $n i64)                ;; zero
    (if (global.get $flag)        ;; give $flag high priority;
        (return (i64.const 7)))   ;;  do not touch $n
    (if (global.get $flag)
        (return (i64.const 8)))
    (if (global.get $flag)
        (return (i64.const 9)))
    (if (global.get $flag)
        (return (i64.const 10)))
    (if (global.get $flag)
        (return (i64.const 11)))
    (if (global.get $flag)
        (return (i64.const 12)))
    (local.set $n                 ;; $n = zero, but this is
      (i64.mul (local.get $n)     ;;  not known because i64.mul
               (local.get $n)))   ;;   is not constant folded
    (if (global.get $flag)        ;; conditionally
        (return (local.get $n)))  ;;  read $n
    (i64.load (i32.const 48))     ;; maybe traps
    drop                          ;;  but ignore result
    (local.get $n))               ;; read $n
  (memory 1)
  (global $flag (mut i32) (i32.const 2)))
`))
```

Back to Bug 1707774 Comment 13