Re: [go-nuts] Is this a compilation optimization bug ?
On Tue, 2022-06-28 at 09:40 -0700, Ian Lance Taylor wrote: > Please open an issue. Thanks. Filed https://go.dev/issue/53600. Dan -- 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/979812a0eaa99be314465dca721fc2426a2f8009.camel%40kortschak.io.
Re: [go-nuts] Is this a compilation optimization bug ?
On Tue, Jun 28, 2022 at 5:47 AM 'Dan Kortschak' via golang-nuts 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 92f0 MOVD $9223372036854775807, R0 > > main.go:4 0x100051554 1402 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 54ad BLE -3(PC) > > main.go:9 0x100051568 d65f03c0 RET > > main.go:9 0x10005156c ? > > ``` > > > > 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.
Re: [go-nuts] Is this a compilation optimization bug ?
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 92f0 MOVD $9223372036854775807, R0 > main.go:4 0x100051554 1402 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 54ad BLE -3(PC) > main.go:9 0x100051568 d65f03c0 RET > main.go:9 0x10005156c ? > ``` > > 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. Dan -- 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/ac0efc0fc8bb57ec2e3fb12b9f69774f28c16e84.camel%40kortschak.io.
[go-nuts] Is this a compilation optimization bug ?
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 92f0 MOVD $9223372036854775807, R0 main.go:4 0x100051554 1402 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 54ad BLE -3(PC) main.go:9 0x100051568 d65f03c0 RET main.go:9 0x10005156c ? ``` 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? -- 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/c4f21dc1-d450-42c8-996f-4f8f1461a9c2n%40googlegroups.com.
