switch.go

Documentation: internal/abi

     1  // Copyright 2023 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package abi
     6  
     7  type InterfaceSwitch struct {
     8  	Cache  *InterfaceSwitchCache
     9  	NCases int
    10  
    11  	// Array of NCases elements.
    12  	// Each case must be a non-empty interface type.
    13  	Cases [1]*InterfaceType
    14  }
    15  
    16  type InterfaceSwitchCache struct {
    17  	Mask    uintptr                      // mask for index. Must be a power of 2 minus 1
    18  	Entries [1]InterfaceSwitchCacheEntry // Mask+1 entries total
    19  }
    20  
    21  type InterfaceSwitchCacheEntry struct {
    22  	// type of source value (a *Type)
    23  	Typ uintptr
    24  	// case # to dispatch to
    25  	Case int
    26  	// itab to use for resulting case variable (a *runtime.itab)
    27  	Itab uintptr
    28  }
    29  
    30  const go122InterfaceSwitchCache = true
    31  
    32  func UseInterfaceSwitchCache(goarch string) bool {
    33  	if !go122InterfaceSwitchCache {
    34  		return false
    35  	}
    36  	// We need an atomic load instruction to make the cache multithreaded-safe.
    37  	// (AtomicLoadPtr needs to be implemented in cmd/compile/internal/ssa/_gen/ARCH.rules.)
    38  	switch goarch {
    39  	case "amd64", "arm64", "loong64", "mips", "mipsle", "mips64", "mips64le", "ppc64", "ppc64le", "riscv64", "s390x":
    40  		return true
    41  	default:
    42  		return false
    43  	}
    44  }
    45  
    46  type TypeAssert struct {
    47  	Cache   *TypeAssertCache
    48  	Inter   *InterfaceType
    49  	CanFail bool
    50  }
    51  type TypeAssertCache struct {
    52  	Mask    uintptr
    53  	Entries [1]TypeAssertCacheEntry
    54  }
    55  type TypeAssertCacheEntry struct {
    56  	// type of source value (a *runtime._type)
    57  	Typ uintptr
    58  	// itab to use for result (a *runtime.itab)
    59  	// nil if CanFail is set and conversion would fail.
    60  	Itab uintptr
    61  }
    62
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