cmd/compile: internal compiler error: bad live variable at entry: [6]string value

[ALTree]

$ gotip version
go version devel go1.17-14a18b7d25 Thu Apr 22 04:07:38 2021 +0000 windows/amd64

package p

func f() {
        var s string
        s = s + "" + s + "" + s + ""
        for true {
        }
}

$ gotip tool compile crash.go
crash.go:5:26: internal compiler error: bad live variable at entry of f: [6]string value

goroutine 20 [running]:
runtime/debug.Stack()
        D:/users/f65362c/alberto/other/gotip/src/runtime/debug/stack.go:24 +0x65
cmd/compile/internal/base.FatalfAt(0xc0000a4a00, 0x95d039, 0x1, 0xc0003d38d0, 0x0, 0xc0000a9354)
        D:/users/f65362c/alberto/other/gotip/src/cmd/compile/internal/base/print.go:227 +0x157
cmd/compile/internal/liveness.(*liveness).epilogue(0xc0000f62c0)
        D:/users/f65362c/alberto/other/gotip/src/cmd/compile/internal/liveness/plive.go:838 +0xc39
cmd/compile/internal/liveness.Compute(0xc0000f62c0, 0xc0003591e0, 0x972918, 0x1)
        D:/users/f65362c/alberto/other/gotip/src/cmd/compile/internal/liveness/plive.go:1353 +0x8f
cmd/compile/internal/ssagen.genssa(0xc0000f62c0, 0xc0003c4f50)
        D:/users/f65362c/alberto/other/gotip/src/cmd/compile/internal/ssagen/ssa.go:6564 +0x9e
cmd/compile/internal/ssagen.Compile(0xc0000f62c0, 0x0)
        D:/users/f65362c/alberto/other/gotip/src/cmd/compile/internal/ssagen/pgen.go:175 +0x266
cmd/compile/internal/gc.compileFunctions.func2.1()
        D:/users/f65362c/alberto/other/gotip/src/cmd/compile/internal/gc/compile.go:130 +0x65
created by cmd/compile/internal/gc.compileFunctions.func2
        D:/users/f65362c/alberto/other/gotip/src/cmd/compile/internal/gc/compile.go:128 +0xcf

Tentatively putting as relblocker in the 1.17 milestone since it's a tip regression, but feel free to re-label.

cc @randall77

[cuonglm]

Also cc @cherrymui @aclements @dr2chase, as this is on triggered with regabiargs enabled:

GOEXPERIMENT=regabiargs GOARCH=amd64 go tool compile issue45693.go

Compile succeed with:

GOEXPERIMENT=noregabiargs GOARCH=amd64 go tool compile issue45693.go

[cherrymui]

Thanks. I'll take a look.

[gopherbot]

Change https://golang.org/cl/312670 mentions this issue: cmd/compile: keep call's args in elim dead auto pass