Hacker News Reader

What go compiler are you using? On my machine those run in exactly the same amount of time (go version go1.9 linux/amd64 ).

  $ ./tmp.test -test.bench .
  goos: linux
  goarch: amd64
  BenchmarkInLoop-4       2000000000               0.46 ns/op
  BenchmarkOutLoop-4      2000000000               0.46 ns/op
  PASS


  (pprof) disasm fast
  Total: 1.95s
  ROUTINE ======================== _/tmp.fast
       970ms      970ms (flat, cum) 49.74% of Total
           .          .     4ed7c0: MOVQ 0x8(SP), AX                             ;main_test.go:23
           .          .     4ed7c5: XORL CX, CX
           .          .     4ed7c7: MOVQ CX, DX
           .          .     4ed7ca: JMP 0x4ed7d6                             ;main_test.go:26
       660ms      660ms     4ed7cc: LEAQ 0x1(CX), BX                             ;_/tmp.fast main_test.go:26
       110ms      110ms     4ed7d0: MOVQ CX, DX
       170ms      170ms     4ed7d3: MOVQ BX, CX
        30ms       30ms     4ed7d6: CMPQ AX, CX
           .          .     4ed7d9: JL 0x4ed7cc                               ;main_test.go:26
           .          .     4ed7db: MOVQ DX, 0x10(SP)                           ;main_test.go:30
  (pprof) disasm slow
  Total: 1.95s
  ROUTINE ======================== _/tmp.slow
       960ms      960ms (flat, cum) 49.23% of Total
           .          .     4ed790: MOVQ 0x8(SP), AX                             ;main_test.go:14
           .          .     4ed795: XORL CX, CX
           .          .     4ed797: MOVQ CX, DX
           .          .     4ed79a: JMP 0x4ed7a6                             ;main_test.go:16
       690ms      690ms     4ed79c: LEAQ 0x1(CX), BX                             ;_/tmp.slow main_test.go:16
       100ms      100ms     4ed7a0: MOVQ CX, DX
       100ms      100ms     4ed7a3: MOVQ BX, CX
        70ms       70ms     4ed7a6: CMPQ AX, CX
           .          .     4ed7a9: JL 0x4ed79c                               ;main_test.go:16
           .          .     4ed7ab: MOVQ DX, 0x10(SP)                           ;main_test.go:20

View on HN

$ ./main.test -test.bench . -test.cpuprofile=test.profile goos: linux goarch: amd64 BenchmarkInLoop-8 2000000000 0.42 ns/op BenchmarkOutLoop-8 2000000000 0.47 ns/op PASS (pprof) disasm fast Total: 1.86s ROUTINE ======================== command-line-arguments.fast 990ms 990ms (flat, cum) 53.23% of Total . . 4ed7b0: MOVQ 0x8(SP), AX ;mem_test.go:16 . . 4ed7b5: XORL CX, CX . . 4ed7b7: MOVQ CX, DX . . 4ed7ba: JMP 0x4ed7c6 ;mem_test.go:19 650ms 650ms 4ed7bc: LEAQ 0x1(CX), BX ;command-line-arguments.fast mem_test.go:19 . . 4ed7c0: MOVQ CX, DX ;mem_test.go:19 10ms 10ms 4ed7c3: MOVQ BX, CX ;command-line-arguments.fast mem_test.go:19 330ms 330ms 4ed7c6: CMPQ AX, CX . . 4ed7c9: JL 0x4ed7bc ;mem_test.go:19 . . 4ed7cb: MOVQ DX, 0x10(SP) ;mem_test.go:23 (pprof) disasm slow Total: 1.86s ROUTINE ======================== command-line-arguments.slow 870ms 870ms (flat, cum) 46.77% of Total . . 4ed780: MOVQ 0x8(SP), AX ;mem_test.go:7 . . 4ed785: XORL CX, CX . . 4ed787: MOVQ CX, DX . . 4ed78a: JMP 0x4ed796 ;mem_test.go:9 560ms 560ms 4ed78c: LEAQ 0x1(CX), BX ;command-line-arguments.slow mem_test.go:9 . . 4ed790: MOVQ CX, DX ;mem_test.go:9 20ms 20ms 4ed793: MOVQ BX, CX ;command-line-arguments.slow mem_test.go:9 290ms 290ms 4ed796: CMPQ AX, CX . . 4ed799: JL 0x4ed78c ;mem_test.go:9 . . 4ed79b: MOVQ DX, 0x10(SP) ;mem_test.go:13