[go-nuts] go compile for memory allocation

[刘桂祥]

//  example1.go
packge main

func main() {
         s := make([]byte, 1024, 1024)
         _ = s
}

s will be allocated in stack and lookup assembl 
<http://www.baidu.com/link?url=bAdrFLMvrfjd9qsjbYka0iztFO6qpJRgzpG6mzu9MrOtl8wUl4TmNVbQ19uYLjU75_lCRcNmRHuiocgN4N9QITmue5XAaqLYQOh9YQzpGi_>e
 
code  not call runtime.makeslice

// example2.go
packge main

func main() {
         cap := 1024
         s := make([]byte, 1024, cap)
         _ = s
}

s will be allocated in heap and lookup assemble code there is 
runtime.makeslice   why this ???

// example3.go
package main

func main() {
       a := 100
       if a>1 {
             a = 1000
       }
       b := interface{}(a)
       _ = b
}

0x0000 00000 (example1.go:3) TEXT "".main(SB), $64-0
0x0000 00000 (example1.go:3) MOVQ (TLS), CX
0x0009 00009 (example1.go:3) CMPQ SP, 16(CX)
0x000d 00013 (example1.go:3) JLS 93
0x000f 00015 (example1.go:3) SUBQ $64, SP
0x0013 00019 (example1.go:3) MOVQ BP, 56(SP)
0x0018 00024 (example1.go:3) LEAQ 56(SP), BP
0x001d 00029 (example1.go:3) FUNCDATA $0, gclocals·33cdeccccebe80329
f1fdbee7f5874cb(SB)
0x001d 00029 (example1.go:3) FUNCDATA $1, gclocals·33cdeccccebe80329
f1fdbee7f5874cb(SB)
0x001d 00029 (example1.go:8) MOVQ $1000, "".autotmp_0+48(SP)
0x0026 00038 (example1.go:8) MOVQ $0, "".autotmp_1+40(SP)
0x002f 00047 (example1.go:8) LEAQ type.int(SB), AX
0x0036 00054 (example1.go:8) MOVQ AX, (SP)
0x003a 00058 (example1.go:8) LEAQ "".autotmp_0+48(SP), AX
0x003f 00063 (example1.go:8) MOVQ AX, 8(SP)
0x0044 00068 (example1.go:8) LEAQ "".autotmp_1+40(SP), AX
0x0049 00073 (example1.go:8) MOVQ AX, 16(SP)
0x004e 00078 (example1.go:8) PCDATA $0, $0
0x004e 00078 (example1.go:8) CALL runtime.convT2E(SB)
0x0053 00083 (example1.go:10) MOVQ 56(SP), BP
0x0058 00088 (example1.go:10) ADDQ $64, SP
0x005c 00092 (example1.go:10) RET
0x005d 00093 (example1.go:10) NOP
0x005d 00093 (example1.go:3) CALL runtime.morestack_noctxt(SB)
0x0062 00098 (example1.go:3) JMP 0


lookup the assemble code and see the compiler is very clever to opt that 
but in example2.go why don't do this 

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