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cmd/compile: internal compiler error: not lowered: v94, Int64Make INT64 INT32 UINT32 #21517

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dvyukov opened this issue Aug 18, 2017 · 5 comments
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cmd/compile: internal compiler error: not lowered: v94, Int64Make INT64 INT32 UINT32 #21517

dvyukov opened this issue Aug 18, 2017 · 5 comments
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FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done.
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Go1.9

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@dvyukov
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dvyukov commented Aug 18, 2017

go version devel +59413d34c9 Fri Aug 18 06:59:48 2017 +0000 linux/amd64

Checkout github.com/google/syzkaller on 172189e9551b768d48c6d5c038fbf3d5cd88aa8e, run:

$ GOARCH=arm go install github.com/google/syzkaller/pkg/ifuzz

produces:

# github.com/google/syzkaller/pkg/ifuzz
pkg/ifuzz/ifuzz.go:254:2: internal compiler error: not lowered: v94, Int64Make INT64 INT32 UINT32

goroutine 69 [running]:
runtime/debug.Stack(0x0, 0x0, 0x0)
	go/src/runtime/debug/stack.go:24 +0xa7
cmd/compile/internal/gc.Fatalf(0xb5bd5d, 0x2, 0xc4240db230, 0x1, 0x1)
	go/src/cmd/compile/internal/gc/subr.go:181 +0x1f4
cmd/compile/internal/gc.(*ssafn).Fatalf(0xc4241d1500, 0xfe0200000012, 0xb5bd5d, 0x2, 0xc4240db230, 0x1, 0x1)
	go/src/cmd/compile/internal/gc/ssa.go:5093 +0x67
cmd/compile/internal/ssa.(*Func).Fatalf(0xc4241eaa00, 0xb5bd5d, 0x2, 0xc4240db230, 0x1, 0x1)
	go/src/cmd/compile/internal/ssa/func.go:496 +0x78
cmd/compile/internal/ssa.checkLower(0xc4241eaa00)
	go/src/cmd/compile/internal/ssa/lower.go:36 +0x35c
cmd/compile/internal/ssa.Compile(0xc4241eaa00)
	go/src/cmd/compile/internal/ssa/compile.go:70 +0x2bb
cmd/compile/internal/gc.buildssa(0xc420534f20, 0x2, 0x0)
	go/src/cmd/compile/internal/gc/ssa.go:216 +0xd39
cmd/compile/internal/gc.compileSSA(0xc420534f20, 0x2)
	go/src/cmd/compile/internal/gc/pgen.go:241 +0x3c
cmd/compile/internal/gc.compileFunctions.func2(0xc4205578c0, 0xc420d6a430, 0x2)
	go/src/cmd/compile/internal/gc/pgen.go:290 +0x49
created by cmd/compile/internal/gc.compileFunctions
	go/src/cmd/compile/internal/gc/pgen.go:288 +0x10e

The code is simply:

func generateInt(cfg *Config, r *rand.Rand, size int) uint64 {
        if size != 1 && size != 2 && size != 4 && size != 8 {  // LINE 254
@dvyukov dvyukov mentioned this issue Aug 18, 2017
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@ALTree
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ALTree commented Aug 18, 2017 •
edited

That line indication is misleading, it's not the if that triggers the crash. Here's a small reproducer:

package p

//go:noinline
func f() uint64 { return 0 }

func g() uint64 {
	return f() % (1 << 63)
}

Gives:

$ gotip version
go version devel +66a1d37bf7 Fri Aug 18 09:28:16 2017 +0000 linux/amd64

$ GOARCH=arm gotip build prova.go
# command-line-arguments
./prova.go:7:2: internal compiler error: not lowered: v8, Int64Make UINT64 UINT32 UINT32

goroutine 34 [running]:
runtime/debug.Stack(0x0, 0x0, 0x0)
	/home/alberto/go/src/runtime/debug/stack.go:24 +0xa7
cmd/compile/internal/gc.Fatalf(0xb5bd5d, 0x2, 0xc4204be0e0, 0x1, 0x1)
	/home/alberto/go/src/cmd/compile/internal/gc/subr.go:181 +0x1f4
cmd/compile/internal/gc.(*ssafn).Fatalf(0xc4204b2000, 0x70200000002, 0xb5bd5d, 0x2, 0xc4204be0e0, 0x1, 0x1)
	/home/alberto/go/src/cmd/compile/internal/gc/ssa.go:5093 +0x67
cmd/compile/internal/ssa.(*Func).Fatalf(0xc4204b4000, 0xb5bd5d, 0x2, 0xc4204be0e0, 0x1, 0x1)
	/home/alberto/go/src/cmd/compile/internal/ssa/func.go:496 +0x78
cmd/compile/internal/ssa.checkLower(0xc4204b4000)
	/home/alberto/go/src/cmd/compile/internal/ssa/lower.go:36 +0x35c
cmd/compile/internal/ssa.Compile(0xc4204b4000)
	/home/alberto/go/src/cmd/compile/internal/ssa/compile.go:70 +0x2bb
cmd/compile/internal/gc.buildssa(0xc420318160, 0x1, 0x0)
	/home/alberto/go/src/cmd/compile/internal/gc/ssa.go:216 +0xd39
cmd/compile/internal/gc.compileSSA(0xc420318160, 0x1)
	/home/alberto/go/src/cmd/compile/internal/gc/pgen.go:241 +0x3c
cmd/compile/internal/gc.compileFunctions.func2(0xc42049c000, 0xc420494020, 0x1)
	/home/alberto/go/src/cmd/compile/internal/gc/pgen.go:290 +0x49
created by cmd/compile/internal/gc.compileFunctions
	/home/alberto/go/src/cmd/compile/internal/gc/pgen.go:288 +0x10e

I can reproduce this with tip and with go1.9rc2. Not with go1.8.3

@ALTree ALTree added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Aug 18, 2017
@cherrymui
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It is this code

v = uint64(r.Int63()) % (1 << 63)

that causes problem.

Normally 64-bit div/mod is turned into runtime calls on 32-bit arch, but the front end leaves power-of-two constant division and hopes the SSA backend turns into a shift or AND. The SSA rule is

(Mod64u <t> n (Const64 [c])) && isPowerOfTwo(c)            -> (And64 n (Const64 <t> [c-1]))

But isPowerOfTwo returns true only for possitive int64

func isPowerOfTwo(n int64) bool {
	return n > 0 && n&(n-1) == 0
}

In this case, however, c==1<<63, doesn't trigger the rule...

@cherrymui
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Also reproducible with Go 1.9rc2, but not with Go 1.8. Mark as Go 1.9 issue.

@cherrymui cherrymui added this to the Go1.9 milestone Aug 18, 2017
@gopherbot
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Change https://golang.org/cl/56890 mentions this issue: cmd/compile: add rules handling unsigned div/mod by constant 1<<63

@ALTree ALTree added NeedsFix The path to resolution is known, but the work has not been done. and removed NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. labels Aug 18, 2017
@gopherbot
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Change https://golang.org/cl/57070 mentions this issue: [release-branch.go1.9] cmd/compile: add rules handling unsigned div/mod by constant 1<<63

gopherbot pushed a commit that referenced this issue Aug 18, 2017
@cherrymui
[release-branch.go1.9] cmd/compile: add rules handling unsigned div/m…
5927854 
…od by constant 1<<63

Cherry-pick CL 56890.

Normally 64-bit div/mod is turned into runtime calls on 32-bit
arch, but the front end leaves power-of-two constant division
and hopes the SSA backend turns into a shift or AND. The SSA rule is

(Mod64u <t> n (Const64 [c])) && isPowerOfTwo(c) -> (And64 n (Const64 <t> [c-1]))

But isPowerOfTwo returns true only for positive int64, which leaves
out 1<<63 unhandled. Add a special case for 1<<63.

Fixes #21517.

Change-Id: Ic91f86fd5e035a8bb64b937c15cb1c38fec917d6
Reviewed-on: https://go-review.googlesource.com/57070
Run-TryBot: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
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