stage2: implement `@setAlignStack` and 128-bit cmpxchg

 * test runner is improved to respect `error.SkipZigTest`
 * start code is improved to `@setAlignStack(16)` before calling main()
 * the newly passing behavior test has a workaround for the fact that
   stage2 cannot yet call `std.Target.x86.featureSetHas()` at comptime.
   This is blocking on comptime closures. The workaround is that there
   is a new decl `@import("builtin").stage2_x86_cx16` which is a `bool`.
 * Implement `@setAlignStack`. This language feature should be re-evaluated
   at some point - I'll file an issue for it.
 * LLVM backend: apply/remove the cold attribute and noinline attribute
   where appropriate.
 * LLVM backend: loads and stores are properly annotated with alignment
   and volatile attributes.
 * LLVM backend: allocas are properly annotated with alignment.
 * Type: fix integers reporting wrong alignment for 256-bit integers and
   beyond. Once you get to 16 byte aligned, there is no further
   alignment for larger integers.

4 files changed, 33 insertions, 28 deletions

diff --git a/test/behavior/atomics.zig b/test/behavior/atomics.zig
index 51cafdf564..aae187739b 100644
--- a/test/behavior/atomics.zig
+++ b/test/behavior/atomics.zig
@@ -81,3 +81,33 @@ test "cmpxchg with ignored result" {
 
     try expect(5678 == x);
 }
+
+test "128-bit cmpxchg" {
+    try test_u128_cmpxchg();
+    comptime try test_u128_cmpxchg();
+}
+
+fn test_u128_cmpxchg() !void {
+    if (builtin.zig_is_stage2) {
+        if (builtin.stage2_arch != .x86_64) return error.SkipZigTest;
+        if (!builtin.stage2_x86_cx16) return error.SkipZigTest;
+    } else {
+        if (builtin.cpu.arch != .x86_64) return error.SkipZigTest;
+        if (comptime !std.Target.x86.featureSetHas(builtin.cpu.features, .cx16)) return error.SkipZigTest;
+    }
+
+    var x: u128 = 1234;
+    if (@cmpxchgWeak(u128, &x, 99, 5678, .SeqCst, .SeqCst)) |x1| {
+        try expect(x1 == 1234);
+    } else {
+        @panic("cmpxchg should have failed");
+    }
+
+    while (@cmpxchgWeak(u128, &x, 1234, 5678, .SeqCst, .SeqCst)) |x1| {
+        try expect(x1 == 1234);
+    }
+    try expect(x == 5678);
+
+    try expect(@cmpxchgStrong(u128, &x, 5678, 42, .SeqCst, .SeqCst) == null);
+    try expect(x == 42);
+}
diff --git a/test/behavior/atomics_stage1.zig b/test/behavior/atomics_stage1.zig
index 8c77ea75b2..c9e0ea1a60 100644
--- a/test/behavior/atomics_stage1.zig
+++ b/test/behavior/atomics_stage1.zig
@@ -3,31 +3,6 @@ const expect = std.testing.expect;
 const expectEqual = std.testing.expectEqual;
 const builtin = @import("builtin");
 
-test "128-bit cmpxchg" {
-    try test_u128_cmpxchg();
-    comptime try test_u128_cmpxchg();
-}
-
-fn test_u128_cmpxchg() !void {
-    if (std.Target.current.cpu.arch != .x86_64) return error.SkipZigTest;
-    if (comptime !std.Target.x86.featureSetHas(std.Target.current.cpu.features, .cx16)) return error.SkipZigTest;
-
-    var x: u128 = 1234;
-    if (@cmpxchgWeak(u128, &x, 99, 5678, .SeqCst, .SeqCst)) |x1| {
-        try expect(x1 == 1234);
-    } else {
-        @panic("cmpxchg should have failed");
-    }
-
-    while (@cmpxchgWeak(u128, &x, 1234, 5678, .SeqCst, .SeqCst)) |x1| {
-        try expect(x1 == 1234);
-    }
-    try expect(x == 5678);
-
-    try expect(@cmpxchgStrong(u128, &x, 5678, 42, .SeqCst, .SeqCst) == null);
-    try expect(x == 42);
-}
-
 var a_global_variable = @as(u32, 1234);
 
 test "cmpxchg on a global variable" {
diff --git a/test/cases.zig b/test/cases.zig
index 64fe39e07b..59f0ef7146 100644
--- a/test/cases.zig
+++ b/test/cases.zig
@@ -26,7 +26,7 @@ pub fn addCases(ctx: *TestContext) !void {
         var case = ctx.exe("hello world with updates", linux_x64);
 
         case.addError("", &[_][]const u8{
-            ":90:9: error: struct 'tmp.tmp' has no member named 'main'",
+            ":95:9: error: struct 'tmp.tmp' has no member named 'main'",
         });
 
         // Incorrect return type
diff --git a/test/stage2/darwin.zig b/test/stage2/darwin.zig
index 86c2d313a0..959313f021 100644
--- a/test/stage2/darwin.zig
+++ b/test/stage2/darwin.zig
@@ -12,9 +12,9 @@ pub fn addCases(ctx: *TestContext) !void {
             .os_tag = .macos,
         };
         {
-            var case = ctx.exe("hello world with updates", target);
+            var case = ctx.exe("darwin hello world with updates", target);
             case.addError("", &[_][]const u8{
-                ":90:9: error: struct 'tmp.tmp' has no member named 'main'",
+                ":95:9: error: struct 'tmp.tmp' has no member named 'main'",
             });
 
             // Incorrect return type