[dev.simd] simd, cmd/compile: mark simd vectors uncomparable

SIMD vector types are opqaue, and are expected to be operated with
methods. It is not always possible to compare the two vectors
efficiently. Instead of adding more magic to the compiler to
handle the == operator, mark the vector types uncomparable.

Change-Id: I4ca5d5e80ca7d8992dffa7b3c0386b75eb19cfa8
Reviewed-on: https://go-review.googlesource.com/c/go/+/705855
Reviewed-by: Junyang Shao <shaojunyang@google.com>
TryBot-Bypass: Cherry Mui <cherryyz@google.com>
Reviewed-by: David Chase <drchase@google.com>

src/cmd/compile/internal/types/size.go

@@ -465,7 +465,7 @@ func CalcSize(t *Type) {
 // by the compiler except for the space that they reserve.
 func simdify(st *Type, isTag bool) {
 	st.align = 8
-	st.alg = AMEM
+	st.alg = ANOALG // not comparable with ==
 	st.intRegs = 0
 	st.isSIMD = true
 	if isTag {

src/simd/_gen/simdgen/gen_simdTypes.go

@@ -129,7 +129,7 @@ const simdTypesTemplates = `
 {{define "sizeTmpl"}}
 // v{{.}} is a tag type that tells the compiler that this is really {{.}}-bit SIMD
 type v{{.}} struct {
-	_{{.}} struct{}
+	_{{.}} [0]func() // uncomparable
 }
 {{end}}
 

src/simd/internal/simd_test/simd_test.go

@@ -54,6 +54,20 @@ func TestType(t *testing.T) {
 	}
 }
 
+func TestUncomparable(t *testing.T) {
+	// Test that simd vectors are not comparable
+	var x, y any = simd.LoadUint32x4(&[4]uint32{1, 2, 3, 4}), simd.LoadUint32x4(&[4]uint32{5, 6, 7, 8})
+	shouldPanic := func(fn func()) {
+		defer func() {
+			if recover() == nil {
+				panic("did not panic")
+			}
+		}()
+		fn()
+	}
+	shouldPanic(func() { _ = x == y })
+}
+
 func TestFuncValue(t *testing.T) {
 	// Test that simd intrinsic can be used as a function value.
 	xv := [4]int32{1, 2, 3, 4}

src/simd/types_amd64.go

@@ -6,7 +6,7 @@ package simd
 
 // v128 is a tag type that tells the compiler that this is really 128-bit SIMD
 type v128 struct {
-	_128 struct{}
+	_128 [0]func() // uncomparable
 }
 
 // Float32x4 is a 128-bit SIMD vector of 4 float32
@@ -433,7 +433,7 @@ func (x Mask64x2) ToBits() uint8
 
 // v256 is a tag type that tells the compiler that this is really 256-bit SIMD
 type v256 struct {
-	_256 struct{}
+	_256 [0]func() // uncomparable
 }
 
 // Float32x8 is a 256-bit SIMD vector of 8 float32
@@ -860,7 +860,7 @@ func (x Mask64x4) ToBits() uint8
 
 // v512 is a tag type that tells the compiler that this is really 512-bit SIMD
 type v512 struct {
-	_512 struct{}
+	_512 [0]func() // uncomparable
 }
 
 // Float32x16 is a 512-bit SIMD vector of 16 float32