cmd/compile: generate code that type checks when inlining variadic functions

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 <khr@golang.org>

1 files changed, 19 insertions, 0 deletions

diff --git a/test/inline_variadic.go b/test/inline_variadic.go
new file mode 100644
index 0000000000..6466c2b093
--- /dev/null
+++ b/test/inline_variadic.go
@@ -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
+}