cmd/compile: missed optimization when using verbose array initialization #54612
Description
What version of Go are you using (go version)?
$ go version go version devel go1.20-8d57f4dcef Sat Aug 20 00:56:30 2022 +0000 linux/amd64
Does this issue reproduce with the latest release?
Yes, reproduces with Go 1.19
What operating system and processor architecture are you using (go env)?
linux/amd64
What did you do?
package pkg
func pack1(id uint64) [5]byte {
var b [5]byte
b[0] = byte(id)
b[1] = byte(id >> 8)
b[2] = byte(id >> 16)
b[3] = byte(id >> 24)
b[4] = byte(id >> 32)
return b
}
func pack2(id uint64) [5]byte {
return [5]byte{
byte(id),
byte(id >> 8),
byte(id >> 16),
byte(id >> 24),
byte(id >> 32),
}
}
What did you expect to see?
I expected both versions to compile the same.
What did you see instead?
pack2 is optimized better than pack1.
command-line-arguments.pack1 STEXT nosplit size=79 args=0x10 locals=0x10 funcid=0x0 align=0x0
0x0000 00000 (/home/dominikh/prj/src/example.com/foo.go:3) TEXT command-line-arguments.pack1(SB), NOSPLIT|ABIInternal, $16-16
0x0000 00000 (/home/dominikh/prj/src/example.com/foo.go:3) SUBQ $16, SP
0x0004 00004 (/home/dominikh/prj/src/example.com/foo.go:3) MOVQ BP, 8(SP)
0x0009 00009 (/home/dominikh/prj/src/example.com/foo.go:3) LEAQ 8(SP), BP
0x000e 00014 (/home/dominikh/prj/src/example.com/foo.go:3) FUNCDATA $0, gclocals·g2BeySu+wFnoycgXfElmcg==(SB)
0x000e 00014 (/home/dominikh/prj/src/example.com/foo.go:3) FUNCDATA $1, gclocals·g2BeySu+wFnoycgXfElmcg==(SB)
0x000e 00014 (/home/dominikh/prj/src/example.com/foo.go:3) FUNCDATA $5, command-line-arguments.pack1.arginfo1(SB)
0x000e 00014 (/home/dominikh/prj/src/example.com/foo.go:3) FUNCDATA $6, command-line-arguments.pack1.argliveinfo(SB)
0x000e 00014 (/home/dominikh/prj/src/example.com/foo.go:3) PCDATA $3, $1
0x000e 00014 (/home/dominikh/prj/src/example.com/foo.go:3) MOVL $0, command-line-arguments.~r0+24(SP)
0x0016 00022 (/home/dominikh/prj/src/example.com/foo.go:3) MOVB $0, command-line-arguments.~r0+28(SP)
0x001b 00027 (/home/dominikh/prj/src/example.com/foo.go:4) MOVL $0, command-line-arguments.b+3(SP)
0x0023 00035 (/home/dominikh/prj/src/example.com/foo.go:4) MOVB $0, command-line-arguments.b+7(SP)
0x0028 00040 (/home/dominikh/prj/src/example.com/foo.go:8) MOVL AX, command-line-arguments.b+3(SP)
0x002c 00044 (/home/dominikh/prj/src/example.com/foo.go:9) SHRQ $32, AX
0x0030 00048 (/home/dominikh/prj/src/example.com/foo.go:9) MOVB AL, command-line-arguments.b+7(SP)
0x0034 00052 (/home/dominikh/prj/src/example.com/foo.go:11) MOVL command-line-arguments.b+3(SP), AX
0x0038 00056 (/home/dominikh/prj/src/example.com/foo.go:11) MOVBLZX command-line-arguments.b+7(SP), CX
0x003d 00061 (/home/dominikh/prj/src/example.com/foo.go:11) MOVL AX, command-line-arguments.~r0+24(SP)
0x0041 00065 (/home/dominikh/prj/src/example.com/foo.go:11) MOVB CL, command-line-arguments.~r0+28(SP)
0x0045 00069 (/home/dominikh/prj/src/example.com/foo.go:11) MOVQ 8(SP), BP
0x004a 00074 (/home/dominikh/prj/src/example.com/foo.go:11) ADDQ $16, SP
0x004e 00078 (/home/dominikh/prj/src/example.com/foo.go:11) RET
0x0000 48 83 ec 10 48 89 6c 24 08 48 8d 6c 24 08 c7 44 H...H.l$.H.l$..D
0x0010 24 18 00 00 00 00 c6 44 24 1c 00 c7 44 24 03 00 $......D$...D$..
0x0020 00 00 00 c6 44 24 07 00 89 44 24 03 48 c1 e8 20 ....D$...D$.H..
0x0030 88 44 24 07 8b 44 24 03 0f b6 4c 24 07 89 44 24 .D$..D$...L$..D$
0x0040 18 88 4c 24 1c 48 8b 6c 24 08 48 83 c4 10 c3 ..L$.H.l$.H....
command-line-arguments.pack2 STEXT nosplit size=26 args=0x10 locals=0x0 funcid=0x0 align=0x0
0x0000 00000 (/home/dominikh/prj/src/example.com/foo.go:14) TEXT command-line-arguments.pack2(SB), NOSPLIT|ABIInternal, $0-16
0x0000 00000 (/home/dominikh/prj/src/example.com/foo.go:14) FUNCDATA $0, gclocals·g2BeySu+wFnoycgXfElmcg==(SB)
0x0000 00000 (/home/dominikh/prj/src/example.com/foo.go:14) FUNCDATA $1, gclocals·g2BeySu+wFnoycgXfElmcg==(SB)
0x0000 00000 (/home/dominikh/prj/src/example.com/foo.go:14) FUNCDATA $5, command-line-arguments.pack2.arginfo1(SB)
0x0000 00000 (/home/dominikh/prj/src/example.com/foo.go:14) FUNCDATA $6, command-line-arguments.pack2.argliveinfo(SB)
0x0000 00000 (/home/dominikh/prj/src/example.com/foo.go:14) PCDATA $3, $1
0x0000 00000 (/home/dominikh/prj/src/example.com/foo.go:14) MOVL $0, command-line-arguments.~r0+8(SP)
0x0008 00008 (/home/dominikh/prj/src/example.com/foo.go:14) MOVB $0, command-line-arguments.~r0+12(SP)
0x000d 00013 (/home/dominikh/prj/src/example.com/foo.go:15) MOVL AX, command-line-arguments.~r0+8(SP)
0x0011 00017 (/home/dominikh/prj/src/example.com/foo.go:20) SHRQ $32, AX
0x0015 00021 (/home/dominikh/prj/src/example.com/foo.go:15) MOVB AL, command-line-arguments.~r0+12(SP)
0x0019 00025 (/home/dominikh/prj/src/example.com/foo.go:15) RET
0x0000 c7 44 24 08 00 00 00 00 c6 44 24 0c 00 89 44 24 .D$......D$...D$
0x0010 08 48 c1 e8 20 88 44 24 0c c3 .H.. .D$..