diff --git a/src/cmd/compile/internal/ssa/tighten.go b/src/cmd/compile/internal/ssa/tighten.go
index 93bb8d048a..eb5007b26e 100644
--- a/src/cmd/compile/internal/ssa/tighten.go
+++ b/src/cmd/compile/internal/ssa/tighten.go
@@ -27,6 +27,8 @@ func tighten(f *Func) {
 	defer f.Cache.freeValueSlice(startMem)
 	endMem := f.Cache.allocValueSlice(f.NumBlocks())
 	defer f.Cache.freeValueSlice(endMem)
+	distinctArgs := f.newSparseSet(f.NumValues())
+	defer f.retSparseSet(distinctArgs)
 	memState(f, startMem, endMem)
 
 	for _, b := range f.Blocks {
@@ -47,16 +49,18 @@ func tighten(f *Func) {
 				// Nil checks need to stay in their block. See issue 72860.
 				continue
 			}
-			// Count arguments which will need a register.
-			narg := 0
+			// Count distinct arguments which will need a register.
+			distinctArgs.clear()
+
 			for _, a := range v.Args {
 				// SP and SB are special registers and have no effect on
 				// the allocation of general-purpose registers.
 				if a.needRegister() && a.Op != OpSB && a.Op != OpSP {
-					narg++
+					distinctArgs.add(a.ID)
 				}
 			}
-			if narg >= 2 && !v.Type.IsFlags() {
+
+			if distinctArgs.size() >= 2 && !v.Type.IsFlags() {
 				// Don't move values with more than one input, as that may
 				// increase register pressure.
 				// We make an exception for flags, as we want flag generators