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cmd/compile: add special case for testing first field of struct variable

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The change to the write barrier in https://golang.org/cl/16899 means
that the compiler now emits tests of the first field of a struct.  That
was using a register that was not used before.  This change fixes that
for amd64 by adding a special case for the first field of a struct.

Update #12416.

Change-Id: Ia57baa62cd741592fbeb9be82f1e846be73d6edd
Reviewed-on: https://go-review.googlesource.com/16933
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
This commit is contained in:
Ian Lance Taylor 2015-11-14 15:42:49 -08:00
parent be1ef46775
commit 9aed0b7e3d
2 changed files with 20 additions and 1 deletions
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10
src/cmd/compile/internal/amd64/gsubr.go
View File

@ -108,7 +108,15 @@ func ginscmp(op gc.Op, t *gc.Type, n1, n2 *gc.Node, likely int) *obj.Prog {
}
// General case.
var r1, r2, g1, g2 gc.Node
if n1.Op == gc.ONAME && n1.Class&gc.PHEAP == 0 || n1.Op == gc.OINDREG {
// A special case to make write barriers more efficient.
// Comparing the first field of a named struct can be done directly.
base := n1
if n1.Op == gc.ODOT && n1.Left.Type.Etype == gc.TSTRUCT && n1.Left.Type.Type.Sym == n1.Right.Sym {
base = n1.Left
}
if base.Op == gc.ONAME && base.Class&gc.PHEAP == 0 || n1.Op == gc.OINDREG {
r1 = *n1
} else {
gc.Regalloc(&r1, t, n1)

11
src/cmd/compile/internal/gc/gsubr.go
View File

@ -404,6 +404,17 @@ func Naddr(a *obj.Addr, n *Node) {
a.Sym = Linksym(s)
case ODOT:
// A special case to make write barriers more efficient.
// Taking the address of the first field of a named struct
// is the same as taking the address of the struct.
if n.Left.Type.Etype != TSTRUCT || n.Left.Type.Type.Sym != n.Right.Sym {
Debug['h'] = 1
Dump("naddr", n)
Fatalf("naddr: bad %v %v", Oconv(int(n.Op), 0), Ctxt.Dconv(a))
}
Naddr(a, n.Left)
case OLITERAL:
if Thearch.Thechar == '8' {
a.Width = 0