simplified aligned allocation; improved codegen; fix mi_good_size with padding included; add MI_MAX_ALIGN_GUARANTEE

include/mimalloc/types.h

@@ -200,6 +200,9 @@ typedef int32_t  mi_ssize_t;
 #error "mimalloc internal: define more bins"
 #endif
 
+// Maximum block size for which blocks are guarenteed to be block size aligned. (see `segment.c:_mi_segment_page_start`)
+#define MI_MAX_ALIGN_GUARANTEE   (MI_MEDIUM_OBJ_SIZE_MAX)
+
 // Alignments over MI_BLOCK_ALIGNMENT_MAX are allocated in dedicated huge page segments
 #define MI_BLOCK_ALIGNMENT_MAX   (MI_SEGMENT_SIZE >> 1)