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cmd/compile: arm64Negate for floating point is not correct #43619

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lijunchen opened this issue Jan 11, 2021 · 5 comments
Closed

cmd/compile: arm64Negate for floating point is not correct #43619

lijunchen opened this issue Jan 11, 2021 · 5 comments
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@lijunchen
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What version of Go are you using (go version)?

master

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

linux/arm64

What did you do?

package main

import (
        "fmt"
        "math"
)

//go:noinline
func test(a, b float64, x uint64) uint64 {
        if a < b {
                x = 0
        }
        return x
}

func main() {
        nan := math.NaN()
        fmt.Println(test(1, nan, 123))
}

What did you expect to see?

123

What did you see instead?

0
@lijunchen
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I have figured out what happened, create this issue to get an issue id for writing a test file.

@davecheney
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NaN is neither less than or greater than any number

https://play.golang.org/p/fYag0Dp6i0i

I don't think this is a bug.

@erifan
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erifan commented Jan 11, 2021

NaN is neither less than or greater than any number

Yes, you are right. So the above case really seems to be a bug.

@gopherbot
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Change https://golang.org/cl/283572 mentions this issue: cmd/compile: fix wrong complement for arm64 floating-point comparisons

@lijunchen
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NaN is neither less than or greater than any number

https://play.golang.org/p/fYag0Dp6i0i

I don't think this is a bug.

If we disable optimization, the output is 123 as expected. So there must be something wrong, I submit a patch, please take a look, thanks.

$ go run -gcflags -N t.go
123

$ go run t.go
0

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@davecheney @gopherbot @erifan @lijunchen