cmd/compile: internal compiler error: untyped type mismatch, have: untyped float, want: untyped int

[ianlancetaylor]

On current tip (874b313, CL 247477) this valid code gets an incorrect compilation error.

I believe this is due to CL 255217. CC @cuonglm @mdempsky

package p

func F(s string) bool {
	const m = 16
	const n = 1e5
	_ = make([]int, n)
	return len(s) < n*m
}

[ianlancetaylor]

Sorry, I forgot to include the compilation error.

foo.go:7:19: internal compiler error: untyped type mismatch, have: untyped float, want: untyped int

goroutine 1 [running]:
runtime/debug.Stack(0xd6b500, 0xc0000ba008, 0x0)
	/home/iant/go/src/runtime/debug/stack.go:24 +0x9f
cmd/compile/internal/gc.Fatalf(0xc73811, 0x29, 0xc0000cc620, 0x2, 0x2)
	/home/iant/go/src/cmd/compile/internal/gc/subr.go:199 +0x1b0
cmd/compile/internal/gc.setconst(0xc0003b6000, 0xc3bec0, 0xc0000a1ad0)
	/home/iant/go/src/cmd/compile/internal/gc/const.go:981 +0x35c
cmd/compile/internal/gc.evconst(0xc0003b6000)
	/home/iant/go/src/cmd/compile/internal/gc/const.go:581 +0x785
cmd/compile/internal/gc.typecheck1(0xc0003b6000, 0x2, 0x0)
	/home/iant/go/src/cmd/compile/internal/gc/typecheck.go:2099 +0x2c5
cmd/compile/internal/gc.typecheck(0xc0003b6000, 0x2, 0x0)
	/home/iant/go/src/cmd/compile/internal/gc/typecheck.go:300 +0x735
cmd/compile/internal/gc.typecheck1(0xc0003b6080, 0x12, 0x0)
	/home/iant/go/src/cmd/compile/internal/gc/typecheck.go:593 +0x2c1c
cmd/compile/internal/gc.typecheck(0xc0003b6080, 0x12, 0x0)
	/home/iant/go/src/cmd/compile/internal/gc/typecheck.go:300 +0x735
cmd/compile/internal/gc.typecheckslice(0xc0000ba448, 0x1, 0x1, 0x12)
	/home/iant/go/src/cmd/compile/internal/gc/typecheck.go:118 +0x51
cmd/compile/internal/gc.typecheckargs(0xc0003b6100)
	/home/iant/go/src/cmd/compile/internal/gc/typecheck.go:2140 +0x96
cmd/compile/internal/gc.typecheck1(0xc0003b6100, 0x1, 0x0)
	/home/iant/go/src/cmd/compile/internal/gc/typecheck.go:2036 +0xa94e
cmd/compile/internal/gc.typecheck(0xc0003b6100, 0x1, 0x0)
	/home/iant/go/src/cmd/compile/internal/gc/typecheck.go:300 +0x735
cmd/compile/internal/gc.typecheckslice(0xc0003a1a80, 0x4, 0x4, 0x1)
	/home/iant/go/src/cmd/compile/internal/gc/typecheck.go:118 +0x51
cmd/compile/internal/gc.Main(0xc81008)
	/home/iant/go/src/cmd/compile/internal/gc/main.go:624 +0x2cb0
main.main()
	/home/iant/go/src/cmd/compile/main.go:52 +0xb1

[mdempsky]

Thanks. Looks like this is related to a pre-existing type-checking bug related to make. For example, this program is valid and type checks with gccgo and go/types, but not with Go 1.15:

package main

func main() {
	const n = 1e5
	_ = make([]int, n)
	f := n
	var _ float64 = f
}

Edit: Go 1.15's error message is:

x.go:7:6: cannot use f (type int) as type float64 in assignment

(Positively, it successfully compiles at tip, likely thanks to CL 255217.)

[cuonglm]

@mdempsky Is it normal that const n = 1e5 is untyped float, but the n.Val().Ctype() is CTINT?

[mdempsky]

@cuonglm No, that's the issue. If a Node has type Idealfloat, then it should have value CTFLT.

[cuonglm]

@cuonglm No, that's the issue. If a Node has type Idealfloat, then it should have value CTFLT.

So I think that's the bug here. I can't find where we currently set that information. This bug does exists before CL 255217, it just works because we assign the value to n instead of doing assertion.

[mdempsky]

@cuonglm That's my assessment too. I have a fix. Will upload shortly.

[gopherbot]

Change https://golang.org/cl/257966 mentions this issue: cmd/compile: fix type checking of "make" arguments