cmd/compile: fix order of map iteration in deadlocals

This makes builds reproducible again.

Fixes #68672
Updates #65158

Change-Id: I260180f52e992c702ab89050deb6484087ae265f
Reviewed-on: https://go-review.googlesource.com/c/go/+/602075
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Than McIntosh <thanm@google.com>

diff --git a/src/cmd/compile/internal/deadlocals/deadlocals.go b/src/cmd/compile/internal/deadlocals/deadlocals.go
index f40ca719700f04dc88e69ee72e8f585e83af4d6e..8bc04b7ff0fe0185623d1f2fcc563b3a65594790 100644 (file)
--- a/src/cmd/compile/internal/deadlocals/deadlocals.go
+++ b/src/cmd/compile/internal/deadlocals/deadlocals.go
@@ -30,7 +30,8 @@ func Funcs(fns []*ir.Func) {
                v := newVisitor(fn)
                v.nodes(fn.Body)
 
-               for _, assigns := range v.defs {
+               for _, k := range v.defsKeys {
+                       assigns := v.defs[k]
                        for _, as := range assigns {
                                // Kludge for "missing func info" linker panic.
                                // See also closureInitLSym in inline/inl.go.
@@ -51,7 +52,8 @@ type visitor struct {
        curfn *ir.Func
        // defs[name] contains assignments that can be discarded if name can be discarded.
        // if defs[name] is defined nil, then name is actually used.
-       defs map[*ir.Name][]assign
+       defs     map[*ir.Name][]assign
+       defsKeys []*ir.Name // insertion order of keys, for reproducible iteration (and builds)
 
        doNode func(ir.Node) bool
 }
@@ -96,9 +98,11 @@ func (v *visitor) node(n ir.Node) {
                n = n.Canonical()
                if isLocal(n, false) {
                        // Force any lazy definitions.
-                       s := v.defs[n]
+                       s, ok := v.defs[n]
+                       if !ok {
+                               v.defsKeys = append(v.defsKeys, n)
+                       }
                        v.defs[n] = nil
-
                        for _, as := range s {
                                // do the visit that was skipped in v.assign when as was appended to v.defs[n]
                                v.node(*as.rhs)
@@ -161,6 +165,9 @@ func (v *visitor) assign(pos src.XPos, lhs, rhs *ir.Node, blankIsNotUse bool) {
        if isLocal(name, blankIsNotUse) && !hasEffects(*rhs) {
                if s, ok := v.defs[name]; !ok || s != nil {
                        // !ok || s != nil is FALSE if previously "v.defs[name] = nil" -- that marks a use.
+                       if !ok {
+                               v.defsKeys = append(v.defsKeys, name)
+                       }
                        v.defs[name] = append(s, assign{pos, lhs, rhs})
                        return // don't visit rhs unless that node ends up live, later.
                }