[dev.regabi] cmd/compile: separate out address taken computation from typechecker

This CL computes a second parallel addrtaken bit that we check
against the old way of doing it. A subsequent CL will rip out the
typechecker code and just use the new way.

Change-Id: I62b7342c44f694144844695386f80088bbd40bf4
Reviewed-on: https://go-review.googlesource.com/c/go/+/275695
Trust: Keith Randall <khr@golang.org>
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>

1 files changed, 48 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/typecheck/subr.go b/src/cmd/compile/internal/typecheck/subr.go
index 178eba4484..8d31fea9ec 100644
--- a/src/cmd/compile/internal/typecheck/subr.go
+++ b/src/cmd/compile/internal/typecheck/subr.go
@@ -67,9 +67,57 @@ func NodAddr(n ir.Node) *ir.AddrExpr {
 
 // nodAddrPos returns a node representing &n at position pos.
 func NodAddrAt(pos src.XPos, n ir.Node) *ir.AddrExpr {
+	n = markAddrOf(n)
 	return ir.NewAddrExpr(pos, n)
 }
 
+func markAddrOf(n ir.Node) ir.Node {
+	if incrementalAddrtaken {
+		// We can only do incremental addrtaken computation when it is ok
+		// to typecheck the argument of the OADDR. That's only safe after the
+		// main typecheck has completed.
+		// The argument to OADDR needs to be typechecked because &x[i] takes
+		// the address of x if x is an array, but not if x is a slice.
+		// Note: outervalue doesn't work correctly until n is typechecked.
+		n = typecheck(n, ctxExpr)
+		if x := ir.OuterValue(n); x.Op() == ir.ONAME {
+			x.Name().SetAddrtaken2(true)
+		}
+	} else {
+		// Remember that we built an OADDR without computing the Addrtaken bit for
+		// its argument. We'll do that later in bulk using computeAddrtaken.
+		dirtyAddrtaken = true
+	}
+	return n
+}
+
+// If incrementalAddrtaken is false, we do not compute Addrtaken for an OADDR Node
+// when it is built. The Addrtaken bits are set in bulk by computeAddrtaken.
+// If incrementalAddrtaken is true, then when an OADDR Node is built the Addrtaken
+// field of its argument is updated immediately.
+var incrementalAddrtaken = false
+
+// If dirtyAddrtaken is true, then there are OADDR whose corresponding arguments
+// have not yet been marked as Addrtaken.
+var dirtyAddrtaken = false
+
+func computeAddrtaken(top []ir.Node) {
+	for _, n := range top {
+		ir.Visit(n, func(n ir.Node) {
+			if n.Op() == ir.OADDR {
+				if x := ir.OuterValue(n.(*ir.AddrExpr).X); x.Op() == ir.ONAME {
+					x.Name().SetAddrtaken2(true)
+					if x.Name().IsClosureVar() {
+						// Mark the original variable as Addrtaken so that capturevars
+						// knows not to pass it by value.
+						x.Name().Defn.Name().SetAddrtaken2(true)
+					}
+				}
+			}
+		})
+	}
+}
+
 func NodNil() ir.Node {
 	n := ir.NewNilExpr(base.Pos)
 	n.SetType(types.Types[types.TNIL])