Hello,
I believe I've found a code-optimization bug in Go 1.21.4 on Linux s390x.
This is what I was able to narrow the code sample down to:
//////////
package main
import "fmt"
type myStruct struct {
A uint32
B uint32
}
func doOpOnStructElems(a, b uint32) uint64 {
return (uint64(a) << 32) | uint64(b)
}
func main() {
myVal := myStruct{0, 0xABCDEF12}
passAsMyStructAndThenDoOp(myVal)
passAsIfaceAndThenDoOp(myVal)
}
func passAsMyStructAndThenDoOp(myVal myStruct) {
fmt.Printf("%X\n", doOpOnStructElems(myVal.A, myVal.B))
}
func passAsIfaceAndThenDoOp(myIface interface{}) {
fmt.Printf("%X\n", doOpOnStructElems(myIface.(myStruct).A,
myIface.(myStruct).B))
}
////////
When I run it I get:
/////
$ go run scratch_1.go
ABCDEF12
ABCDEF12000000
//////
If I run it on Linux zSeries w/ Go 1.20.11 or on Linux AMD64, Linux ARM64,
or macOS w/ Go 1.21.4, I get what I believe is the correct answer:
////
$ go run scratch_1.go
ABCDEF12
ABCDEF12
////
In other words, with Go 1.21.4 and s390x it appears that A & B are switched
in the 2nd call which passes the struct as an interface{} .
s390x is the only big endian platform I am able to test on. So I suspect
there may be an endianness issue here. I suspect something has gone wrong
with some sort of code optimization because if I insert Println() at the
beginning of doOpOnStructElems(), the problem goes away. So it's possible
there's some bug with code inlining when what is being passed in was
originally passed in as an interface in the caller?
If someone could confirm that this is indeed a bug I will be happy to file
an issue.
Thank you,
Tim
3:35 <https://mongodb.slack.com/archives/C0V3YK738/p1701203702444689>
package main import ( "fmt" ) type myStruct struct { A uint32 B uint32 }
func doOpOnStructElems(a, b uint32) int64 { return int64((uint64(a) << 32)
| uint64(b)) } func main() { myVal := myStruct{0, 0xFFFF}
passAsMyStructAndThenDoOp(myVal) passAsIfaceAndThenDoOp(myVal) } func
passAsMyStructAndThenDoOp(myVal myStruct) { fmt.Printf("%X\n",
doOpOnStructElems(myVal.A, myVal.B)) } func passAsIfaceAndThenDoOp(myIface
interface{}) { fmt.Printf("%X\n", doOpOnStructElems(myIface.(myStruct).A,
myIface.(myStruct).B)) }
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