test/codegen: make sure assignment results are used.

Some tests make assignments to an argument without reading it.
With CL 708865, they are treated as dead stores and are removed.
Make sure the results are used.

Fixes #75745.
Fixes #75746.

Change-Id: I05580beb1006505ec1550e5fa245b54dcefd10b9
Reviewed-on: https://go-review.googlesource.com/c/go/+/708916
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>

Author: cherrymui

test/codegen/constants.go

@@ -7,7 +7,7 @@
 package codegen
 
 // A uint16 or sint16 constant shifted left.
-func shifted16BitConstants(out [64]uint64) {
+func shifted16BitConstants() (out [64]uint64) {
 	// ppc64x: "MOVD\t[$]8193,", "SLD\t[$]27,"
 	out[0] = 0x0000010008000000
 	// ppc64x: "MOVD\t[$]-32767", "SLD\t[$]26,"
@@ -16,10 +16,11 @@ func shifted16BitConstants(out [64]uint64) {
 	out[2] = 0xFFFF000000000000
 	// ppc64x: "MOVD\t[$]65535", "SLD\t[$]44,"
 	out[3] = 0x0FFFF00000000000
+	return
 }
 
 // A contiguous set of 1 bits, potentially wrapping.
-func contiguousMaskConstants(out [64]uint64) {
+func contiguousMaskConstants() (out [64]uint64) {
 	// ppc64x: "MOVD\t[$]-1", "RLDC\tR[0-9]+, [$]44, [$]63,"
 	out[0] = 0xFFFFF00000000001
 	// ppc64x: "MOVD\t[$]-1", "RLDC\tR[0-9]+, [$]43, [$]63,"
@@ -30,4 +31,5 @@ func contiguousMaskConstants(out [64]uint64) {
 	// ppc64x/power9: "MOVD\t[$]-1", "RLDC\tR[0-9]+, [$]33, [$]63,"
 	// ppc64x/power10: "MOVD\t[$]-8589934591,"
 	out[3] = 0xFFFFFFFE00000001
+	return
 }

test/codegen/mathbits.go

@@ -731,7 +731,7 @@ func Add64MPanicOnOverflowGT(a, b [2]uint64) [2]uint64 {
 //
 // This is what happened on PPC64 when compiling
 // crypto/internal/edwards25519/field.feMulGeneric.
-func Add64MultipleChains(a, b, c, d [2]uint64) {
+func Add64MultipleChains(a, b, c, d [2]uint64) [2]uint64 {
 	var cx, d1, d2 uint64
 	a1, a2 := a[0], a[1]
 	b1, b2 := b[0], b[1]
@@ -748,6 +748,7 @@ func Add64MultipleChains(a, b, c, d [2]uint64) {
 	d2, _ = bits.Add64(c2, d2, cx)
 	d[0] = d1
 	d[1] = d2
+	return d
 }
 
 // --------------- //