Bug 1325771 - mfbt: Reorder parameters for MOZ_ALIGNED_DECL r=jwalden

Currently, MOZ_ALIGNED_DECL uses the order (_type, _align) for its
parameters. However, this order makes the code less readable when
_type is a larger object like a struct because the value for _align
would be at the end of the struct definition. By swapping the order
of _type and _align, the alignment value will always be next to
the type name, regardless how far the definition of _type extends.

Differential Revision: https://phabricator.services.mozilla.com/D77288

js/src/jsapi-tests/testAtomicOperations.cpp

@@ -85,8 +85,8 @@ END_TEST(testAtomicFence)
 // Memory for testing atomics.  This must be aligned to the natural alignment of
 // the type we're testing; for now, use 8-byte alignment for all.
 
-MOZ_ALIGNED_DECL(static uint8_t atomicMem[8], 8);
-MOZ_ALIGNED_DECL(static uint8_t atomicMem2[8], 8);
+MOZ_ALIGNED_DECL(8, static uint8_t atomicMem[8]);
+MOZ_ALIGNED_DECL(8, static uint8_t atomicMem2[8]);
 
 // T is the primitive type we're testing, and A and B are references to constant
 // bindings holding values of that type.

js/src/wasm/WasmTypes.h

@@ -2874,7 +2874,7 @@ struct TlsData {
   // The globalArea must be the last field.  Globals for the module start here
   // and are inline in this structure.  16-byte alignment is required for SIMD
   // data.
-  MOZ_ALIGNED_DECL(char globalArea, 16);
+  MOZ_ALIGNED_DECL(16, char globalArea);
 };
 
 static const size_t TlsDataAlign = 16;  // = Simd128DataSize

mfbt/Alignment.h

@@ -62,18 +62,18 @@ struct AlignasHelper {
  *
  * For instance,
  *
- *   MOZ_ALIGNED_DECL(char arr[2], 8);
+ *   MOZ_ALIGNED_DECL(8, char arr[2]);
  *
  * will declare a two-character array |arr| aligned to 8 bytes.
  */
 
 #if defined(__GNUC__)
-#  define MOZ_ALIGNED_DECL(_type, _align) _type __attribute__((aligned(_align)))
+#  define MOZ_ALIGNED_DECL(_align, _type) _type __attribute__((aligned(_align)))
 #elif defined(_MSC_VER)
-#  define MOZ_ALIGNED_DECL(_type, _align) __declspec(align(_align)) _type
+#  define MOZ_ALIGNED_DECL(_align, _type) __declspec(align(_align)) _type
 #else
 #  warning "We don't know how to align variables on this compiler."
-#  define MOZ_ALIGNED_DECL(_type, _align) _type
+#  define MOZ_ALIGNED_DECL(_align, _type) _type
 #endif
 
 /*
@@ -92,27 +92,27 @@ struct AlignedElem;
 
 template <>
 struct AlignedElem<1> {
-  MOZ_ALIGNED_DECL(uint8_t elem, 1);
+  MOZ_ALIGNED_DECL(1, uint8_t elem);
 };
 
 template <>
 struct AlignedElem<2> {
-  MOZ_ALIGNED_DECL(uint8_t elem, 2);
+  MOZ_ALIGNED_DECL(2, uint8_t elem);
 };
 
 template <>
 struct AlignedElem<4> {
-  MOZ_ALIGNED_DECL(uint8_t elem, 4);
+  MOZ_ALIGNED_DECL(4, uint8_t elem);
 };
 
 template <>
 struct AlignedElem<8> {
-  MOZ_ALIGNED_DECL(uint8_t elem, 8);
+  MOZ_ALIGNED_DECL(8, uint8_t elem);
 };
 
 template <>
 struct AlignedElem<16> {
-  MOZ_ALIGNED_DECL(uint8_t elem, 16);
+  MOZ_ALIGNED_DECL(16, uint8_t elem);
 };
 
 template <typename T>