issue80577.go

     1  // run
     2  
     3  // Copyright 2026 The Go Authors. All rights reserved.
     4  // Use of this source code is governed by a BSD-style
     5  // license that can be found in the LICENSE file.
     6  
     7  // Issue 80577: on riscv64, sign extensions were elided after
     8  // 32-bit instructions that architecturally sign-extend their
     9  // result, but an unsigned-typed value spilled across a call is
    10  // restored with a zero-extending load, losing the elided
    11  // sign extension.
    12  
    13  package main
    14  
    15  import "math/bits"
    16  
    17  var sink uint32
    18  
    19  //go:noinline
    20  func use(x uint32) { sink = x }
    21  
    22  //go:noinline
    23  func mul(a, b uint32) int64 {
    24  	p := a * b
    25  	use(p) // p live across the call, forcing a spill
    26  	return int64(int32(p))
    27  }
    28  
    29  //go:noinline
    30  func div(a, b uint32) int64 {
    31  	p := a / b
    32  	use(p)
    33  	return int64(int32(p))
    34  }
    35  
    36  //go:noinline
    37  func rem(a, b uint32) int64 {
    38  	p := a % b
    39  	use(p)
    40  	return int64(int32(p))
    41  }
    42  
    43  //go:noinline
    44  func rot(a uint32, k int) int64 {
    45  	p := bits.RotateLeft32(a, k)
    46  	use(p)
    47  	return int64(int32(p))
    48  }
    49  
    50  func main() {
    51  	const want = -2147483648
    52  	if got := mul(0x8000, 0x10000); got != want {
    53  		println("mul: got", got, "want", want)
    54  		panic("bad mul")
    55  	}
    56  	if got := div(0x80000000, 1); got != want {
    57  		println("div: got", got, "want", want)
    58  		panic("bad div")
    59  	}
    60  	if got := rem(0x80000000, 0xffffffff); got != want {
    61  		println("rem: got", got, "want", want)
    62  		panic("bad rem")
    63  	}
    64  	if got := rot(1, 31); got != want {
    65  		println("rot: got", got, "want", want)
    66  		panic("bad rot")
    67  	}
    68  }
    69
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