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cmd/compile: crash internal compiler error: schedule does not include all values (simple program) #20097

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gwik opened this issue Apr 24, 2017 · 9 comments
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cmd/compile: crash internal compiler error: schedule does not include all values (simple program) #20097

gwik opened this issue Apr 24, 2017 · 9 comments
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Go1.8.3

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@gwik
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gwik commented Apr 24, 2017

What version of Go are you using (go version)?

go version go1.8.1 darwin/amd64

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

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/gwik/go"
GORACE=""
GOROOT="/usr/local/go"
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/st/k_6dl_dx5c919wbcjm0340x00000gp/T/go-build456109878=/tmp/go-build -gno-record-gcc-switches -fno-common"
CXX="clang++"
CGO_ENABLED="1"
PKG_CONFIG="pkg-config"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"

What did you do?

I was writing a simple token bucket algorithm when it failed to compile.
Here is the code, I reduced it to the smallest possible that still trigger the compiler error.

package main

import "time"

type Clock func() time.Time

type bucket struct {
	capacity int64
	tokens   int64
	rate     time.Duration

	lastFill time.Time
	clock    Clock
}

func (b *bucket) Take(i int64) {
	for {
		now := b.clock()
		fill := int64(b.rate) / b.capacity * int64(b.lastFill.Sub(now))
		if fill >= i {
			b.lastFill = now
			b.tokens = fill - i
			return
		}
		time.Sleep(b.rate / time.Duration(b.capacity))
	}
}

func main() {
}

What did you expect to see?

The compilation should succeed or fail because the program is invalid.

What did you see instead?

The compiler crashed with an internal error.

# command-line-arguments
./internalcompilererror.go:17: internal compiler error: schedule does not include all values

goroutine 1 [running]:
runtime/debug.Stack(0x0, 0x0, 0x0)
	/usr/local/go/src/runtime/debug/stack.go:24 +0x79
cmd/compile/internal/gc.Fatalf(0x16c4939, 0x24, 0x0, 0x0, 0x0)
	/usr/local/go/src/cmd/compile/internal/gc/subr.go:167 +0x226
cmd/compile/internal/gc.(*ssaExport).Fatalf(0x19c7b95, 0x11, 0x16c4939, 0x24, 0x0, 0x0, 0x0)
	/usr/local/go/src/cmd/compile/internal/gc/ssa.go:4984 +0x5d
cmd/compile/internal/ssa.(*Config).Fatalf(0xc4203b8000, 0xdffd3db700000011, 0x16c4939, 0x24, 0x0, 0x0, 0x0)
	/usr/local/go/src/cmd/compile/internal/ssa/config.go:343 +0x6e
cmd/compile/internal/ssa.(*Func).Fatalf(0xc420398480, 0x16c4939, 0x24, 0x0, 0x0, 0x0)
	/usr/local/go/src/cmd/compile/internal/ssa/func.go:414 +0x6b
cmd/compile/internal/ssa.schedule(0xc420398480)
	/usr/local/go/src/cmd/compile/internal/ssa/schedule.go:287 +0x126f
cmd/compile/internal/ssa.Compile(0xc420398480)
	/usr/local/go/src/cmd/compile/internal/ssa/compile.go:69 +0x304
cmd/compile/internal/gc.buildssa(0xc420395170, 0x0)
	/usr/local/go/src/cmd/compile/internal/gc/ssa.go:180 +0x918
cmd/compile/internal/gc.compile(0xc420395170)
	/usr/local/go/src/cmd/compile/internal/gc/pgen.go:362 +0x204
cmd/compile/internal/gc.funccompile(0xc420395170)
	/usr/local/go/src/cmd/compile/internal/gc/dcl.go:1292 +0xdc
cmd/compile/internal/gc.Main()
	/usr/local/go/src/cmd/compile/internal/gc/main.go:464 +0x1f08
main.main()
	/usr/local/go/src/cmd/compile/main.go:50 +0xfe
@ALTree ALTree added the NeedsFix The path to resolution is known, but the work has not been done. label Apr 24, 2017
@ALTree
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ALTree commented Apr 24, 2017

Go 1.7.5 is fine
go1.8, go1.8.1 and tip crash

Will try to bisect.

@cherrymui
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    v66 = DIVQ <int64,int64> v28 v32
    v68 = Select0 <time.Duration> v66
    v37 = Select0 <int64> v66

This is the problem. The scheduler assumes a tuple op (DIVQ) can have at most one Select0. But in this case v68 and v37 both are Select0 of v66, but not CSE'd because of the type difference.

@ALTree
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ALTree commented Apr 24, 2017

Git bisect says: "introduced in 25e0a36 (cmd/compile: clean up tuple types and selects)"

@cherrymui
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I tried to make the scheduler accepting more than one Select0's, but there is another problem. The result register is allocated at the tuple op (v66 DIVQ), and the Select0 is just a pesudo-op that doesn't allocate new register. So v68 and v37 use the same register, and both live. Register allocator crashes.
Probably we should CSE the two selectors regardless of type.

@cherrymui
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a simple repro (on AMD64):

type T int64
func f(x, y int64) (int64, T) {
        a := x / y
        b := T(x) / T(y)
        return a, b
}

@randall77 randall77 added this to the Go1.8.2 milestone Apr 24, 2017
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CL https://golang.org/cl/41505 mentions this issue.

@randall77
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Reopening for 1.8.2.

@randall77 randall77 reopened this May 9, 2017
@aclements aclements removed the NeedsFix The path to resolution is known, but the work has not been done. label May 16, 2017
@bradfitz bradfitz modified the milestones: Go1.8.2, Go1.8.3 May 18, 2017
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CL https://golang.org/cl/43997 mentions this issue.

gopherbot pushed a commit that referenced this issue May 23, 2017
@tzneal @bradfitz
[release-branch.go1.8] cmd/compile: ignore types when considering tup…
195e20a 
…le select for CSE

Fixes #20097

Change-Id: I3c9626ccc8cd0c46a7081ea8650b2ff07a5d4fcd
Reviewed-on: https://go-review.googlesource.com/41505
Run-TryBot: Todd Neal <todd@tneal.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-on: https://go-review.googlesource.com/43997
Run-TryBot: Chris Broadfoot <cbro@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
@bradfitz
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Done in https://go-review.googlesource.com/c/43997/

@golang golang locked and limited conversation to collaborators May 23, 2018
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@bradfitz @gwik @aclements @ALTree @randall77 @gopherbot @cherrymui