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cmd/compile: generate code that type checks when inlining variadic fu…
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…nctions

This fixes a bug in -l=3 or higher.

To inline a variadic function, the compiler generates code that constructs
a slice of arguments for the variadic parameter. Consider the function

  func Foo(xs ...string)

and the call Foo("hello", "world"). To inline the call to Foo, the
compiler used to generate

  xs := [2]string{"hello", "world"}[:]

which doesn't type check:

  invalid operation [2]string literal[:] (slice of unaddressable value).

Now, the compiler generates

  xs := []string{"hello", "world"}

which does type check.

Fixes #18116.

Change-Id: I0ee531ef2e6cc276db6fb12602b25a46d6d5db21
Reviewed-on: https://go-review.googlesource.com/33671
Reviewed-by: Keith Randall <[email protected]>
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davidlazar committed Nov 30, 2016
1 parent 01dda42 commit 5d1b53a
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Showing 2 changed files with 21 additions and 3 deletions.
5 changes: 2 additions & 3 deletions src/cmd/compile/internal/gc/inl.go
Original file line number Diff line number Diff line change
Expand Up @@ -781,10 +781,9 @@ func mkinlcall1(n *Node, fn *Node, isddd bool) *Node {
as.Right = nodnil()
as.Right.Type = varargtype
} else {
vararrtype := typArray(varargtype.Elem(), int64(varargcount))
as.Right = nod(OCOMPLIT, nil, typenod(vararrtype))
varslicetype := typSlice(varargtype.Elem())
as.Right = nod(OCOMPLIT, nil, typenod(varslicetype))
as.Right.List.Set(varargs)
as.Right = nod(OSLICE, as.Right, nil)
}

as = typecheck(as, Etop)
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19 changes: 19 additions & 0 deletions test/inline_variadic.go
Original file line number Diff line number Diff line change
@@ -0,0 +1,19 @@
// errorcheck -0 -m -l=3

// Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Test more aggressive inlining (-l=3 allows variadic functions)
// See issue #18116.

package foo

func head(xs ...string) string { // ERROR "can inline head" "leaking param: xs to result"
return xs[0]
}

func f() string { // ERROR "can inline f"
x := head("hello", "world") // ERROR "inlining call to head" "\[\]string literal does not escape"
return x
}

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