cmd/gc: GOARCH=386: invalid reuse of register #4353
Description
When I run this program (reduced from a file generated by test/index.go)
package main
var aib [100000]int
var paib *[100000]int = &aib
var i64 int64 = 100023
func main() {
_ = paib[i64]
}
with GOARCH=amd64 I get
panic: runtime error: index out of range
goroutine 1 [running]:
main.main()
/home/iant/foo3.go:8 +0x3c
goroutine 2 [syscall]:
created by runtime.main
/home/iant/go2/src/pkg/runtime/proc.c:225
exit status 2
When I run it with GOARCH=386 I get
unexpected fault address 0x186b7
throw: fault
[signal 0xb code=0x1 addr=0x186b7 pc=0x8048c3d]
goroutine 1 [running]:
main.main()
/home/iant/foo3.go:8 +0x3d
goroutine 2 [syscall]:
created by runtime.main
/home/iant/go2/src/pkg/runtime/proc.c:225
exit status 2
The GOARCH=amd64 panic is correct: this is an "index out of range." It is not
an "unexpected fault address."
The generated code with GOARCH=386 is
--- prog list "main" ---
0000 (/home/iant/foo3.go:7) TEXT main+0(SB),$0-0
0001 (/home/iant/foo3.go:8) MOVL paib+0(SB),BX
0002 (/home/iant/foo3.go:8) MOVL i64+0(SB),BX
0003 (/home/iant/foo3.go:8) MOVL i64+4(SB),DX
0004 (/home/iant/foo3.go:8) MOVL DX,CX
0005 (/home/iant/foo3.go:8) MOVL BX,AX
0006 (/home/iant/foo3.go:8) CMPL DX,$0
0007 (/home/iant/foo3.go:8) JNE $1,13
0008 (/home/iant/foo3.go:8) MOVL BX,BP
0009 (/home/iant/foo3.go:8) LEAL (BX),SI
0010 (/home/iant/foo3.go:8) TESTB $0,(SI)
0011 (/home/iant/foo3.go:8) CMPL BP,$100000
0012 (/home/iant/foo3.go:8) JCS $1,15
0013 (/home/iant/foo3.go:8) CALL ,runtime.panicindex+0(SB)
0014 (/home/iant/foo3.go:8) UNDEF ,
0015 (/home/iant/foo3.go:8) LEAL (SI)(BP*4),SI
0016 (/home/iant/foo3.go:8) MOVL (SI),AX
0017 (/home/iant/foo3.go:9) RET ,
The problem occurs at the start: the value of paib is loaded into bx (0002). Then the
low-order 32-bit of i64 is loaded into bx (0003). Then we load the contents of bx into
si (0009). That instruction expects bx to hold paib, but instead it holds the low-order
32 bits of i64.