stage2: implement alignment calculation of vectors

closes #11856

Author: andrewrk

lib/std/simd.zig

@@ -160,7 +160,6 @@ pub fn extract(
 }
 
 test "vector patterns" {
-    if (@import("builtin").zig_backend != .stage1) return error.SkipZigTest;
     const base = @Vector(4, u32){ 10, 20, 30, 40 };
     const other_base = @Vector(4, u32){ 55, 66, 77, 88 };
 

src/type.zig

@@ -2906,9 +2906,13 @@ pub const Type = extern union {
 
             .array, .array_sentinel => return ty.elemType().abiAlignmentAdvanced(target, strat),
 
-            // TODO audit this - is there any more complicated logic to determine
-            // ABI alignment of vectors?
-            .vector => return AbiAlignmentAdvanced{ .scalar = 16 },
+            .vector => {
+                const len = ty.arrayLen();
+                const bits = try bitSizeAdvanced(ty.elemType(), target, sema_kit);
+                const bytes = (bits + 7) / 8;
+                const alignment = std.math.ceilPowerOfTwoAssert(u64, bytes * len);
+                return AbiAlignmentAdvanced{ .scalar = @intCast(u32, alignment) };
+            },
 
             .i16, .u16 => return AbiAlignmentAdvanced{ .scalar = intAbiAlignment(16, target) },
             .u29 => return AbiAlignmentAdvanced{ .scalar = intAbiAlignment(29, target) },

test/behavior/vector.zig

@@ -1048,3 +1048,21 @@ test "@shlWithOverflow" {
     try S.doTheTest();
     comptime try S.doTheTest();
 }
+
+test "alignment of vectors" {
+    try expect(@alignOf(@Vector(2, u8)) == 2);
+    try expect(@alignOf(@Vector(2, u1)) == 2);
+    try expect(@alignOf(@Vector(1, u1)) == 1);
+    try expect(@alignOf(@Vector(2, u16)) == 4);
+}
+
+test "loading the second vector from a slice of vectors" {
+    @setRuntimeSafety(false);
+    var small_bases = [2]@Vector(2, u8){
+        @Vector(2, u8){ 0, 1 },
+        @Vector(2, u8){ 2, 3 },
+    };
+    var a: []const @Vector(2, u8) = &small_bases;
+    var a4 = a[1][1];
+    try expect(a4 == 3);
+}