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>

1 files changed, 29 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/ssa/value.go b/src/cmd/compile/internal/ssa/value.go
index ba7f8c0300..630e4814b9 100644
--- a/src/cmd/compile/internal/ssa/value.go
+++ 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