issue79182.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 79182: SHLQconst/SHLLconst rewrite rule for (x+x)<<c
     8  // missed a bounds check on c, causing c+1 to overflow the valid
     9  // shift range and producing incorrect results on amd64.
    10  
    11  package main
    12  
    13  //go:noinline
    14  func shl32(x uint32) uint32 {
    15  	return (x + x) << 31
    16  }
    17  
    18  //go:noinline
    19  func shl64(x uint64) uint64 {
    20  	return (x + x) << 63
    21  }
    22  
    23  func main() {
    24  	if got := shl32(1); got != 0 {
    25  		println("shl32(1) =", got, "want 0")
    26  		panic("FAIL")
    27  	}
    28  	if got := shl64(1); got != 0 {
    29  		println("shl64(1) =", got, "want 0")
    30  		panic("FAIL")
    31  	}
    32  }
    33
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