[Bug go/65772] New: With multiple return values including a function with side effects, incorrect value is returned

[Bug go/65772] New: With multiple return values including a function with side effects, incorrect value is returned

[boger at us dot ibm.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65772

            Bug ID: 65772
           Summary: With multiple return values including a function with
                    side effects, incorrect value is returned
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: go
          Assignee: ian at airs dot com
          Reporter: boger at us dot ibm.com
                CC: cmang at google dot com
            Target: ppc64le, x86_64

[Bug go/65772] With multiple return values including a function with side effects, incorrect value is returned

[boger at us dot ibm.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65772

--- Comment #1 from boger at us dot ibm.com ---
Created attachment 35321
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35321&action=edit
testcase for bad return values

[Bug go/65772] With multiple return values including a function with side effects, incorrect value is returned

[boger at us dot ibm.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65772

--- Comment #2 from boger at us dot ibm.com ---
When running the attached testcase on a platform with gccgo (ppc64le, x86_64),
the test fails due to incorrect return values from the function getList.  The
source line for the return looks like this:

return files, filepath.Walk(dir, visit)

The problem occurs because the array "files" is declared in the getList
function, and updated by the "visit" function which is passed to filepath.Walk.
 The array that is returned from getList does not reflect the updates made by
the visit.

When build with gc for either ppc64le or x86_64, the test case passes.

Expected output:

./myreturn
### Trying to list file: /tmp/mytest465364283/stuff in dir:
/tmp/mytest465364283 ###
### When walking:  found file: /tmp/mytest465364283/stuff ###
### PASS:  files returned !###


Incorrect output:

./myreturn
### Trying to list file: /tmp/mytest819936920/stuff in dir:
/tmp/mytest819936920 ###
### When walking:  found file: /tmp/mytest819936920/stuff ###
### FAIL:  no files returned ###

[Bug go/65772] With multiple return values including a function with side effects, incorrect value is returned

[ian at airs dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65772

Ian Lance Taylor <ian at airs dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID

--- Comment #3 from Ian Lance Taylor <ian at airs dot com> ---
The test case is invalid.  It works coincidentally with gc.

The order of evaluation rules for Go
(http://golang.org/ref/spec#Order_of_evaluation) do not specify when a variable
is read.  In a case like
    return files, filepath.Walk(dir, visit)
where files is updated by the visit function passed to filepath.Walk, the files
variable may be read either before or after calling filepath.Walk.  The gc
compiler is generating code that reads it after, the gccgo compiler is
generating code that reads it before.  Either is correct according to the
language spec.