Add test for __BIGGEST_ALIGNMENT__ and use it over hardcoded constants. NFC (#19728)

Author: sbc100

system/lib/pthread/pthread_create.c

@@ -17,7 +17,7 @@
 #include <emscripten/heap.h>
 #include <emscripten/threading.h>
 
-#define STACK_ALIGN 16
+#define STACK_ALIGN __BIGGEST_ALIGNMENT__
 #define TSD_ALIGN (sizeof(void*))
 
 // Comment this line to enable tracing of thread creation and destruction:

system/lib/wasm_worker/library_wasm_worker.c

@@ -15,7 +15,7 @@
 
 #define ROUND_UP(x, ALIGNMENT) (((x)+ALIGNMENT-1)&-ALIGNMENT)
 #define SBRK_ALIGN (__alignof__(max_align_t))
-#define STACK_ALIGN 16
+#define STACK_ALIGN __BIGGEST_ALIGNMENT__
 
 // Options:
 // #define STACK_OVERFLOW_CHECK 0/1/2 : set to the current stack overflow check mode

test/core/test_core_types.c

@@ -81,6 +81,7 @@
 #error EMSCRIPTEN is not defined
 #endif
 
+#include <stdalign.h>
 #include <stdint.h>
 #include <stddef.h>
 #include <string.h>
@@ -91,22 +92,24 @@
 
 int main() {
 #if __wasm64__
-  assert(sizeof(void*) == 8);
-  assert(sizeof(long) == 8);
-  assert(sizeof(intptr_t) == 8);
-  assert(sizeof(size_t) == 8);
-  assert(sizeof(ptrdiff_t) == 8);
+  assert(__SIZEOF_POINTER__ == 8);
 #else
-  assert(sizeof(void*) == 4);
-  assert(sizeof(long) == 4);
-  assert(sizeof(intptr_t) == 4);
-  assert(sizeof(size_t) == 4);
-  assert(sizeof(ptrdiff_t) == 4);
+  assert(__SIZEOF_POINTER__ == 4);
 #endif
+  assert(sizeof(void*) == __SIZEOF_POINTER__);
+  assert(sizeof(long) == __SIZEOF_POINTER__);
+  assert(sizeof(intptr_t) == __SIZEOF_POINTER__);
+  assert(sizeof(size_t) == __SIZEOF_POINTER__);
+  assert(sizeof(ptrdiff_t) == __SIZEOF_POINTER__);
   assert(sizeof(intmax_t) == 8);
-  assert(__alignof(double) == 8);
+  assert(alignof(double) == 8);
   assert(sizeof(long double) == 16);
-  assert(__alignof(long double) == 8);
+  assert(alignof(long double) == 8);
+  assert(alignof(max_align_t) == 8);
+  // __BIGGEST_ALIGNMENT__ corresponds to the default stack alignment
+  // used by llvm.  Unlike `alignof(max_align_t)` it includes SIMD types.
+  // We use this in emscripten as our default stack alignment.
+  assert(__BIGGEST_ALIGNMENT__ == 16);
   assert(__FLT_EVAL_METHOD__ == 0);
   assert(strcmp(STRINGIZE(__USER_LABEL_PREFIX__), "") == 0);
   return 0;