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cmd/compile: skip convT2E for empty structs

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Fixes #18402

Change-Id: I5af800857fb2e365ce4224eece9171277106ec7d
Reviewed-on: https://go-review.googlesource.com/35562
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
Josh Bleecher Snyder 2017-01-22 10:17:12 -08:00
parent 3d5eb4a6be
commit 8958d8ce37
2 changed files with 20 additions and 10 deletions
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1
src/cmd/compile/internal/gc/go.go
View File

@ -365,6 +365,7 @@ var Thearch Arch
var (
staticbytes,
zerobase,
Newproc,
Deferproc,
Deferreturn,

29
src/cmd/compile/internal/gc/walk.go
View File

@ -894,26 +894,35 @@ opswitch:
staticbytes = newname(Pkglookup("staticbytes", Runtimepkg))
staticbytes.Class = PEXTERN
staticbytes.Type = typArray(Types[TUINT8], 256)
zerobase = newname(Pkglookup("zerobase", Runtimepkg))
zerobase.Class = PEXTERN
zerobase.Type = Types[TUINTPTR]
}
// Optimize convT2{E,I} when T is not pointer-shaped,
// but the value does not escape or is a readonly global or is a bool/byte.
// Optimize convT2{E,I} for many cases in which T is not pointer-shaped,
// by using an existing addressable value identical to n.Left
// or creating one on the stack.
var value *Node
switch {
case !n.Left.Type.IsInterface() && n.Esc == EscNone && n.Left.Type.Width <= 1024:
// Initializing a stack temporary to the value we want to put in the interface,
// then using the address of that stack temporary for the interface data word.
value = temp(n.Left.Type)
init.Append(typecheck(nod(OAS, value, n.Left), Etop))
case n.Left.Class == PEXTERN && n.Left.Name != nil && n.Left.Name.Readonly:
// readonly global; use directly.
value = n.Left
case n.Left.Type.Size() == 0:
// n.Left is zero-sized. Use zerobase.
value = zerobase
case n.Left.Type.IsBoolean() || (n.Left.Type.Size() == 1 && n.Left.Type.IsInteger()):
// n.Left is a bool/byte. Use staticbytes[n.Left].
value = nod(OINDEX, staticbytes, byteindex(n.Left))
value.Bounded = true
case n.Left.Class == PEXTERN && n.Left.Name != nil && n.Left.Name.Readonly:
// n.Left is a readonly global; use it directly.
value = n.Left
case !n.Left.Type.IsInterface() && n.Esc == EscNone && n.Left.Type.Width <= 1024:
// n.Left does not escape. Use a stack temporary initialized to n.Left.
value = temp(n.Left.Type)
init.Append(typecheck(nod(OAS, value, n.Left), Etop))
}
if value != nil {
// Value is identical to n.Left.
// Construct the interface directly: {type/itab, &value}.
var t *Node
if n.Type.IsEmptyInterface() {
t = typename(n.Left.Type)