[dev.regabi] cmd/compile: improve walkReturn common case

Instead of evaluating all result expressions up front and then
assigning them to their result destinations, we can interleave
evaluation with assignment. This reduces how much temporary
stack/register space is needed to hold the values in flight.

Doesn't pass toolstash -cmp, because it allows better return statement
code to be generated. E.g., cmd/go's text segment on linux/ppc64le
shrinks another 1kB.

Change-Id: I3fe889342c80e947e0118704ec01f1682c577e6e
Reviewed-on: https://go-review.googlesource.com/c/go/+/281153
Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>

diff --git a/src/cmd/compile/internal/walk/assign.go b/src/cmd/compile/internal/walk/assign.go
index 04bd576b696d4e528f843d1aeb0556fe2ad5479a..84ba7f0dc5093dccf25c01c0f89056f54c88f584 100644 (file)
--- a/src/cmd/compile/internal/walk/assign.go
+++ b/src/cmd/compile/internal/walk/assign.go
@@ -253,10 +253,9 @@ func walkReturn(n *ir.ReturnStmt) ir.Node {
 
        // Common case: Assignment order doesn't matter. Simply assign to
        // each result parameter in order.
-       walkExprList(n.Results, n.PtrInit())
-       res := make([]ir.Node, len(results))
+       var res ir.Nodes
        for i, v := range n.Results {
-               res[i] = convas(ir.NewAssignStmt(base.Pos, dsts[i], v), n.PtrInit())
+               appendWalkStmt(&res, convas(ir.NewAssignStmt(base.Pos, dsts[i], v), &res))
        }
        n.Results = res
        return n