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cmd/compile: fix stringtoslicebytetmp optimization

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Fixes #14973.

Change-Id: Iea68c9deca9429bde465c9ae05639209fe0ccf72
Reviewed-on: https://go-review.googlesource.com/21175
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
This commit is contained in:
Matthew Dempsky 2016-03-25 21:11:33 -07:00
parent 4ffa5eb876
commit 995fb0319e
2 changed files with 28 additions and 23 deletions
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43
src/cmd/compile/internal/gc/order.go
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@ -705,28 +705,31 @@ func orderstmt(n *Node, order *Order) {
order.out = append(order.out, n)
cleantemp(t, order)
// n->right is the expression being ranged over.
// order it, and then make a copy if we need one.
// We almost always do, to ensure that we don't
// see any value changes made during the loop.
// Usually the copy is cheap (e.g., array pointer, chan, slice, string are all tiny).
// The exception is ranging over an array value (not a slice, not a pointer to array),
// which must make a copy to avoid seeing updates made during
// the range body. Ranging over an array value is uncommon though.
case ORANGE:
t := marktemp(order)
// n.Right is the expression being ranged over.
// order it, and then make a copy if we need one.
// We almost always do, to ensure that we don't
// see any value changes made during the loop.
// Usually the copy is cheap (e.g., array pointer,
// chan, slice, string are all tiny).
// The exception is ranging over an array value
// (not a slice, not a pointer to array),
// which must make a copy to avoid seeing updates made during
// the range body. Ranging over an array value is uncommon though.
// Mark []byte(str) range expression to reuse string backing storage.
// It is safe because the storage cannot be mutated.
if n.Right.Op == OSTRARRAYBYTE {
n.Right.Op = OSTRARRAYBYTETMP
}
t := marktemp(order)
n.Right = orderexpr(n.Right, order, nil)
switch n.Type.Etype {
default:
Fatalf("orderstmt range %v", n.Type)
// Mark []byte(str) range expression to reuse string backing storage.
// It is safe because the storage cannot be mutated.
case TARRAY:
if n.Right.Op == OSTRARRAYBYTE {
n.Right.Op = OSTRARRAYBYTETMP
}
if n.List.Len() < 2 || isblank(n.List.Second()) {
// for i := range x will only use x once, to compute len(x).
// No need to copy it.
@ -734,10 +737,9 @@ func orderstmt(n *Node, order *Order) {
}
fallthrough
// chan, string, slice, array ranges use value multiple times.
// make copy.
// fall through
case TCHAN, TSTRING:
// chan, string, slice, array ranges use value multiple times.
// make copy.
r := n.Right
if r.Type.Etype == TSTRING && r.Type != Types[TSTRING] {
@ -748,12 +750,11 @@ func orderstmt(n *Node, order *Order) {
n.Right = ordercopyexpr(r, r.Type, order, 0)
// copy the map value in case it is a map literal.
// TODO(rsc): Make tmp = literal expressions reuse tmp.
// For maps tmp is just one word so it hardly matters.
case TMAP:
// copy the map value in case it is a map literal.
// TODO(rsc): Make tmp = literal expressions reuse tmp.
// For maps tmp is just one word so it hardly matters.
r := n.Right
n.Right = ordercopyexpr(r, r.Type, order, 0)
// n->alloc is the temp for the iterator.