uglyfib.go

     1  // run
     2  
     3  //go:build !wasm
     4  
     5  // Copyright 2021 The Go Authors. All rights reserved.
     6  // Use of this source code is governed by a BSD-style
     7  // license that can be found in the LICENSE file.
     8  
     9  // wasm is excluded because the compiler chatter about register abi pragma ends up
    10  // on stdout, and causes the expected output to not match.
    11  
    12  package main
    13  
    14  import "fmt"
    15  
    16  // This test is designed to provoke a stack growth
    17  // in a way that very likely leaves junk in the
    18  // parameter save area if they aren't saved or spilled
    19  // there, as appropriate.
    20  
    21  //go:registerparams
    22  //go:noinline
    23  func f(x int, xm1, xm2, p *int) {
    24  	var y = [2]int{x - 4, 0}
    25  	if x < 2 {
    26  		*p += x
    27  		return
    28  	}
    29  	x -= 3
    30  	g(*xm1, xm2, &x, p)   // xm1 is no longer live.
    31  	h(*xm2, &x, &y[0], p) // xm2 is no longer live, but was spilled.
    32  }
    33  
    34  //go:registerparams
    35  //go:noinline
    36  func g(x int, xm1, xm2, p *int) {
    37  	var y = [3]int{x - 4, 0, 0}
    38  	if x < 2 {
    39  		*p += x
    40  		return
    41  	}
    42  	x -= 3
    43  	k(*xm2, &x, &y[0], p)
    44  	h(*xm1, xm2, &x, p)
    45  }
    46  
    47  //go:registerparams
    48  //go:noinline
    49  func h(x int, xm1, xm2, p *int) {
    50  	var y = [4]int{x - 4, 0, 0, 0}
    51  	if x < 2 {
    52  		*p += x
    53  		return
    54  	}
    55  	x -= 3
    56  	k(*xm1, xm2, &x, p)
    57  	f(*xm2, &x, &y[0], p)
    58  }
    59  
    60  //go:registerparams
    61  //go:noinline
    62  func k(x int, xm1, xm2, p *int) {
    63  	var y = [5]int{x - 4, 0, 0, 0, 0}
    64  	if x < 2 {
    65  		*p += x
    66  		return
    67  	}
    68  	x -= 3
    69  	f(*xm2, &x, &y[0], p)
    70  	g(*xm1, xm2, &x, p)
    71  }
    72  
    73  func main() {
    74  	x := 40
    75  	var y int
    76  	xm1 := x - 1
    77  	xm2 := x - 2
    78  	f(x, &xm1, &xm2, &y)
    79  
    80  	fmt.Printf("Fib(%d)=%d\n", x, y)
    81  }
    82
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