On Tue, Jun 28, 2022 at 5:47 AM 'Dan Kortschak' via golang-nuts <golang-nuts@googlegroups.com> wrote: > > On Mon, 2022-06-27 at 23:32 -0700, iori yamada wrote: > > Running the code in the link below times out, is this a bug? > > Looking at the assembly, it seems that the instructions corresponding > > to the if statement have been removed due to optimization. > > > > https://go.dev/play/p/CZX4mbyrp37 > > > > The following is a description of how I thought it was a bug. > > > > In the first loop, the value of i is 9223372036854775807 (the maximum > > value of type int), which is incremented and overflows. Then it > > becomes -9223372036854775808 (minimum value of type int) and I > > thought the condition in the if statement exits from the true > > neighbor loop. > > > > I couldn't figure out where the bug was happening, so I decided to > > look at an assembly of the same code as above, built it locally, and > > checked it with objdump. > > Perhaps, the CMP instruction that compares the conditions of the if > > statement has been removed due to optimization. > > > > ``` > > ... > > TEXT main.main(SB) Path/main.go > > main.go:3 0x100051550 92f00000 MOVD $9223372036854775807, R0 > > main.go:4 0x100051554 14000002 JMP 2(PC) > > main.go:4 0x100051558 91000400 ADD $1, R0, R0 > > main.go:4 0x10005155c 92f0001b MOVD $9223372036854775807, R27 > > main.go:4 0x100051560 eb1b001f CMP R27, R0 > > main.go:4 0x100051564 54ffffad BLE -3(PC) > > main.go:9 0x100051568 d65f03c0 RET > > main.go:9 0x10005156c 00000000 ? > > ``` > > > > So I compiled it without optimization (go build -gcflags '-N -l') and > > the program terminated immediately as intended. > > > > I may have misunderstood something, may I ask anyone to check once? > > Yes, I see the same behaviour when I run this locally (also tried with > an old version go1.14.9). > > Also, the assembly generated at godbolt shows that no code is generated > for the terminating branch https://godbolt.org/z/9jW1GaKfv unless > optimisation is turned off https://godbolt.org/z/o7o6x3bzd.
Interesting. Looks like Go 1.10 got this right, but 1.11 and higher go into an endless loop. gccgo gets it right. Please open an issue. Thanks. Ian -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/CAOyqgcUPy6VdKbmc%2BOCaMDAw3c6FdtJVcLiJBGji1BK-DPzKaQ%40mail.gmail.com.
