cmd/compile: add recursive-invalidate Value method, use in expand_calls

This removes more unused values during transformation.
Leaving them in the tree can create type conflicts in OpArg* references.

Updates #40724.
Updates #44816.
Fixes #45417.

Change-Id: I07dcb7b4b2bf8d79e22e0543cb2fb52c2ececb96
Reviewed-on: https://go-review.googlesource.com/c/go/+/308589
Trust: David Chase <drchase@google.com>
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>

src/cmd/compile/internal/ssa/expand_calls.go

@@ -1015,7 +1015,7 @@ func (x *expandState) rewriteArgs(v *Value, firstArg int) {
 			if x.debug {
 				x.Printf("...marking %v unused\n", a.LongString())
 			}
-			a.reset(OpInvalid)
+			a.invalidateRecursively()
 		}
 	}
 
@@ -1140,7 +1140,7 @@ func expandCalls(f *Func) {
 					if x.debug {
 						x.Printf("...marking %v unused\n", a.LongString())
 					}
-					a.reset(OpInvalid)
+					a.invalidateRecursively()
 				}
 			}
 			if x.debug {
@@ -1343,6 +1343,9 @@ func expandCalls(f *Func) {
 		if dupe == nil {
 			x.commonSelectors[sk] = v
 		} else if x.sdom.IsAncestorEq(dupe.Block, v.Block) {
+			if x.debug {
+				x.Printf("Duplicate, make %s copy of %s\n", v, dupe)
+			}
 			v.copyOf(dupe)
 		} else {
 			// Because values are processed in dominator order, the old common[s] will never dominate after a miss is seen.
@@ -1361,7 +1364,7 @@ func expandCalls(f *Func) {
 			x.Printf("allOrdered[%d] = b%d, %s, uses=%d\n", i, b.ID, v.LongString(), v.Uses)
 		}
 		if v.Uses == 0 {
-			v.reset(OpInvalid)
+			v.invalidateRecursively()
 			continue
 		}
 		if v.Op == OpCopy {
@@ -1456,7 +1459,7 @@ func expandCalls(f *Func) {
 				v.SetArg(i, aa)
 				for a.Uses == 0 {
 					b := a.Args[0]
-					a.reset(OpInvalid)
+					a.invalidateRecursively()
 					a = b
 				}
 			}

src/cmd/compile/internal/ssa/value.go

@@ -348,6 +348,35 @@ func (v *Value) reset(op Op) {
 	v.Aux = nil
 }
 
+// invalidateRecursively marks a value as invalid (unused)
+// and after decrementing reference counts on its Args,
+// also recursively invalidates any of those whose use
+// count goes to zero.
+//
+// BEWARE of doing this *before* you've applied intended
+// updates to SSA.
+func (v *Value) invalidateRecursively() {
+	if v.InCache {
+		v.Block.Func.unCache(v)
+	}
+	v.Op = OpInvalid
+
+	for _, a := range v.Args {
+		a.Uses--
+		if a.Uses == 0 {
+			a.invalidateRecursively()
+		}
+	}
+
+	v.argstorage[0] = nil
+	v.argstorage[1] = nil
+	v.argstorage[2] = nil
+	v.Args = v.argstorage[:0]
+
+	v.AuxInt = 0
+	v.Aux = nil
+}
+
 // copyOf is called from rewrite rules.
 // It modifies v to be (Copy a).
 //go:noinline