I got it, the code is here https://github.com/golang/go/blob/633f9e206045176a12c301eb2c249c1c1d9a5d2e/src/cmd/compile/internal/gc/pgen.go#L186, I don't know why the slot is required to be aligned at least 8 bytes on these architectures. I will try to see if this requirement can be removed on linux/arm64, and to determine the slot size based on the actual size of the variable, just like linux/amd64 does.
在2020年11月4日星期三 UTC+8 上午9:38:12<[email protected]> 写道： > Hi Keith, thank you for your response. Sorry I didn't say that I saw this > issue on linux/arm64. For your example above, the result on linux/arm64 is > like this: > go tool compile -S tmp.go > > 0x001c 00028 (spill.go:4) MOVD "".p(FP), R0 > 0x0020 00032 (spill.go:4) MOVH (R0), R1 > 0x0024 00036 (spill.go:4) MOVH R1, "".x-8(SP) > 0x0028 00040 (spill.go:5) MOVD "".q+8(FP), R2 > 0x002c 00044 (spill.go:5) MOVH (R2), R3 > 0x0030 00048 (spill.go:5) MOVH R3, "".y-16(SP) > 0x0034 00052 (spill.go:6) PCDATA $1, ZR > 0x0034 00052 (spill.go:6) CALL "".g(SB) > 0x0038 00056 (spill.go:7) MOVH "".y-16(SP), R0 > 0x003c 00060 (spill.go:7) MOVD "".p(FP), R1 > 0x0040 00064 (spill.go:7) MOVH R0, (R1) > 0x0044 00068 (spill.go:8) MOVH "".x-8(SP), R0 > 0x0048 00072 (spill.go:8) MOVD "".q+8(FP), R1 > 0x004c 00076 (spill.go:8) MOVH R0, (R1) > > Obviously it is 8 bytes. > 在2020年11月4日星期三 UTC+8 上午6:39:30<Keith Randall> 写道： > >> It don't think it does. For instance, an int16 will be spilled to a >> 2-byte slot in the stack frame. >> Can you show us what you are seeing? This is what I tried: >> >> package main >> >> func f(p, q *int16) { >> x := *p >> y := *q >> g() >> *p = y >> *q = x >> } >> func g() >> >> go tool compile -S tmp.go >> >> 0x001d 00029 (tmp1.go:4) MOVQ "".p+24(SP), AX >> 0x0022 00034 (tmp1.go:4) MOVWLZX (AX), CX >> 0x0025 00037 (tmp1.go:4) MOVW CX, "".x+6(SP) >> 0x002a 00042 (tmp1.go:5) MOVQ "".q+32(SP), DX >> 0x002f 00047 (tmp1.go:5) MOVWLZX (DX), BX >> 0x0032 00050 (tmp1.go:5) MOVW BX, "".y+4(SP) >> 0x0037 00055 (tmp1.go:6) CALL "".g(SB) >> 0x003c 00060 (tmp1.go:7) MOVWLZX "".y+4(SP), AX >> 0x0041 00065 (tmp1.go:7) MOVQ "".p+24(SP), CX >> 0x0046 00070 (tmp1.go:7) MOVW AX, (CX) >> 0x0049 00073 (tmp1.go:8) MOVWLZX "".x+6(SP), AX >> 0x004e 00078 (tmp1.go:8) MOVQ "".q+32(SP), CX >> 0x0053 00083 (tmp1.go:8) MOVW AX, (CX) >> >> >> On Monday, November 2, 2020 at 3:29:49 AM UTC-8 [email protected] wrote: >> >>> Hi, >>> >>> Can someone tell me why does OpStoreReg of type int16, int32, etc. >>> occupy 8 bytes on the stack? And where is this handled ? Thanks. >>> >> -- 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 [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/ebdd0219-ea29-4449-8c6e-e42066da7dedn%40googlegroups.com.
