cmd/compile: should delete loops without side-effects

As of go1.24-cbdb3545ad, none of the following loops get optimized away:

package main

func main() {
    for range 10 {
        // Just an empty loop
    }

    var x int
    for range 20 {
        // x never gets read after the loop
        x++
    }

    var y [30]int
    for i := range y {
        // The bounds check gets optimized out, turning this into an empty loop
        _ = y[i]
    }

    for range "13 characters" {
        // An empty loop that parses UTF-8
    }

    const debugFoo = false
    const debugBar = false
    for range 40 {
        // Loop body is dead and gets optimized out
        if debugFoo {
            println()
        }
        if debugBar {
            println()
        }
    }
}

main.main STEXT size=152 args=0x0 locals=0x20 funcid=0x0 align=0x0
    0x0000 00000 (...../foo.go:3)   TEXT    main.main(SB), ABIInternal, $32-0
    0x0000 00000 (...../foo.go:3)   CMPQ    SP, 16(R14)
    0x0004 00004 (...../foo.go:3)   PCDATA  $0, $-2
    0x0004 00004 (...../foo.go:3)   JLS 142
    0x000a 00010 (...../foo.go:3)   PCDATA  $0, $-1
    0x000a 00010 (...../foo.go:3)   PUSHQ   BP
    0x000b 00011 (...../foo.go:3)   MOVQ    SP, BP
    0x000e 00014 (...../foo.go:3)   SUBQ    $24, SP
    0x0012 00018 (...../foo.go:3)   FUNCDATA    $0, gclocals·M83szM6+gDKfH9vuf1h0yw==(SB)
    0x0012 00018 (...../foo.go:3)   FUNCDATA    $1, gclocals·M83szM6+gDKfH9vuf1h0yw==(SB)
    0x0012 00018 (...../foo.go:3)   XORL    AX, AX
    0x0014 00020 (...../foo.go:4)   JMP 25
    0x0016 00022 (...../foo.go:4)   INCQ    AX
    0x0019 00025 (...../foo.go:4)   CMPQ    AX, $10
    0x001d 00029 (...../foo.go:4)   JLT 22
    0x001f 00031 (...../foo.go:4)   XORL    AX, AX
    0x0021 00033 (...../foo.go:4)   JMP 38
    0x0023 00035 (...../foo.go:9)   INCQ    AX
    0x0026 00038 (...../foo.go:9)   CMPQ    AX, $20
    0x002a 00042 (...../foo.go:9)   JLT 35
    0x002c 00044 (...../foo.go:9)   XORL    AX, AX
    0x002e 00046 (...../foo.go:15)  JMP 51
    0x0030 00048 (...../foo.go:15)  INCQ    AX
    0x0033 00051 (...../foo.go:15)  CMPQ    AX, $30
    0x0037 00055 (...../foo.go:15)  JLT 48
    0x0039 00057 (...../foo.go:15)  XORL    AX, AX
    0x003b 00059 (...../foo.go:15)  JMP 64
    0x003d 00061 (...../foo.go:20)  MOVQ    SI, AX
    0x0040 00064 (...../foo.go:20)  CMPQ    AX, $13
    0x0044 00068 (...../foo.go:20)  JGE 123
    0x0046 00070 (...../foo.go:20)  LEAQ    go:string."13 characters"(SB), DX
    0x004d 00077 (...../foo.go:20)  MOVBLZX (DX)(AX*1), SI
    0x0051 00081 (...../foo.go:20)  CMPL    SI, $128
    0x0057 00087 (...../foo.go:20)  JGE 95
    0x0059 00089 (...../foo.go:20)  LEAQ    1(AX), SI
    0x005d 00093 (...../foo.go:20)  JMP 61
    0x005f 00095 (...../foo.go:20)  MOVL    $13, BX
    0x0064 00100 (...../foo.go:20)  MOVQ    AX, CX
    0x0067 00103 (...../foo.go:20)  MOVQ    DX, AX
    0x006a 00106 (...../foo.go:20)  PCDATA  $1, $0
    0x006a 00106 (...../foo.go:20)  CALL    runtime.decoderune(SB)
    0x006f 00111 (...../foo.go:20)  LEAQ    go:string."13 characters"(SB), DX
    0x0076 00118 (...../foo.go:20)  MOVQ    BX, SI
    0x0079 00121 (...../foo.go:20)  JMP 61
    0x007b 00123 (...../foo.go:20)  XORL    AX, AX
    0x007d 00125 (...../foo.go:20)  JMP 130
    0x007f 00127 (...../foo.go:26)  INCQ    AX
    0x0082 00130 (...../foo.go:26)  CMPQ    AX, $40
    0x0086 00134 (...../foo.go:26)  JLT 127
    0x0088 00136 (...../foo.go:35)  ADDQ    $24, SP
    0x008c 00140 (...../foo.go:35)  POPQ    BP
    0x008d 00141 (...../foo.go:35)  RET
    0x008e 00142 (...../foo.go:35)  NOP
    0x008e 00142 (...../foo.go:3)   PCDATA  $1, $-1
    0x008e 00142 (...../foo.go:3)   PCDATA  $0, $-2
    0x008e 00142 (...../foo.go:3)   CALL    runtime.morestack_noctxt(SB)
    0x0093 00147 (...../foo.go:3)   PCDATA  $0, $-1
    0x0093 00147 (...../foo.go:3)   JMP 0

golang / go

cmd/compile: should delete loops without side-effects #69889