diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 99d355242..5591c84b8 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -25,8 +25,11 @@ jobs:
         with:
           msystem: MINGW64
           update: true
-          install: git binutils mingw-w64-x86_64-mlir mingw-w64-x86_64-cmake mingw-w64-x86_64-toolchain mingw-w64-x86_64-llvm mingw-w64-x86_64-polly mingw-w64-x86_64-python mingw-w64-x86_64-lld
-
+          install: git binutils mingw-w64-x86_64-cmake mingw-w64-x86_64-toolchain mingw-w64-x86_64-python
+      - shell: msys2 {0}
+        run: |
+            pacman --noconfirm -U https://mirror.msys2.org/mingw/mingw64/mingw-w64-x86_64-llvm-13.0.1-2-any.pkg.tar.zst
+            pacman --noconfirm -U https://mirror.msys2.org/mingw/mingw64/mingw-w64-x86_64-lld-13.0.1-2-any.pkg.tar.zst
       - name: CMake
         run: |
           mkdir build && cd build
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 3211051ad..fb878b4e2 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -75,7 +75,7 @@ set(LLVM_LINK_COMPONENTS
         WindowsManifest
         )
 
-if (${LLVM_PACKAGE_VERSION} VERSION_GREATER 14)
+if (${LLVM_PACKAGE_VERSION} VERSION_GREATER 14.1)
     set(LLVM_LINK_COMPONENTS ${LLVM_LINK_COMPONENTS} WindowsDriver)
 endif()
 
diff --git a/lib/std/array.c3 b/lib/std/array.c3
index 3285de1d7..9ed41f25d 100644
--- a/lib/std/array.c3
+++ b/lib/std/array.c3
@@ -4,16 +4,22 @@
 module std::array;
 import std::mem;
 
-macro make($Type, usize elements)
+/**
+ * @require elements > 0
+ **/
+macro alloc($Type, usize elements)
 {
-    assert(elements > 0);
-    $Type* ptr = mem::alloc($sizeof($Type), elements);
+	assert($Type.max / elements < $Type.sizeof);
+    $Type* ptr = mem::alloc($Type.sizeof * elements, $alignof($Type));
     return ptr[0..(elements - 1)];
 }
 
-macro make_zero($Type, usize elements)
+/**
+ * @require elements > 0
+ **/
+macro calloc($Type, usize elements)
 {
-    assert(elements > 0);
-    $Type* ptr = mem::calloc($sizeof($Type), elements);
+	assert($Type.max / elements < $Type.sizeof);
+    $Type* ptr = mem::calloc($sizeof($Type) * elements, $alignof($Type));
     return ptr[0..(elements - 1)];
 }
diff --git a/lib/std/io.c3 b/lib/std/io.c3
index 44beb0e7c..c8ed6459b 100644
--- a/lib/std/io.c3
+++ b/lib/std/io.c3
@@ -11,15 +11,9 @@ struct File
     CFile file;
 }
 
-
-extern fn int _puts(char* message) @extname("puts");
-extern fn int printf(char* message, ...);
-extern fn int _putchar(char c) @extname("putchar");
-
-
 fn int putchar(char c) @inline
 {
-    return _putchar(c);
+    return libc::putchar(c);
 }
 
 /**
@@ -43,7 +37,7 @@ fn int print(char* message)
  */
 fn int println(char *message = "") @inline
 {
-    return _puts(message);
+    return libc::puts(message);
 }
 
 fn void! File.open(File* file, char[] filename, char[] mode)
@@ -202,319 +196,3 @@ fn void File.error(File *file) @inline
     int err = ferror
 }
 */
-/*
-
-#define	__SLBF	0x0001		/* line buffered */
-#define	__SNBF	0x0002		/* unbuffered */
-#define	__SRD	0x0004		/* OK to read */
-#define	__SWR	0x0008		/* OK to write */
-	/* RD and WR are never simultaneously asserted */
-#define	__SRW	0x0010		/* open for reading & writing */
-#define	__SEOF	0x0020		/* found EOF */
-#define	__SERR	0x0040		/* found error */
-#define	__SMBF	0x0080		/* _buf is from malloc */
-#define	__SAPP	0x0100		/* fdopen()ed in append mode */
-#define	__SSTR	0x0200		/* this is an sprintf/snprintf string */
-#define	__SOPT	0x0400		/* do fseek() optimisation */
-#define	__SNPT	0x0800		/* do not do fseek() optimisation */
-#define	__SOFF	0x1000		/* set iff _offset is in fact correct */
-#define	__SMOD	0x2000		/* true => fgetln modified _p text */
-#define __SALC  0x4000		/* allocate string space dynamically */
-#define __SIGN  0x8000		/* ignore this file in _fwalk */
-
-/*
- * The following three definitions are for ANSI C, which took them
- * from System V, which brilliantly took internal interface macros and
- * made them official arguments to setvbuf(), without renaming them.
- * Hence, these ugly _IOxxx names are *supposed* to appear in user code.
- *
- * Although numbered as their counterparts above, the implementation
- * does not rely on this.
- */
-#define	_IOFBF	0		/* setvbuf should set fully buffered */
-#define	_IOLBF	1		/* setvbuf should set line buffered */
-#define	_IONBF	2		/* setvbuf should set unbuffered */
-
-#define	BUFSIZ	1024		/* size of buffer used by setbuf */
-#define	EOF	(-1)
-
-				/* must be == _POSIX_STREAM_MAX <limits.h> */
-#define	FOPEN_MAX	20	/* must be <= OPEN_MAX <sys/syslimits.h> */
-#define	FILENAME_MAX	1024	/* must be <= PATH_MAX <sys/syslimits.h> */
-
-/* System V/ANSI C; this is the wrong way to do this, do *not* use these. */
-#ifndef _ANSI_SOURCE
-#define	P_tmpdir	"/var/tmp/"
-#endif
-#define	L_tmpnam	1024	/* XXX must be == PATH_MAX */
-#define	TMP_MAX		308915776
-
-
-#define	stdin	__stdinp
-#define	stdout	__stdoutp
-#define	stderr	__stderrp
-
-
-/* ANSI-C */
-
-__BEGIN_DECLS
-char	*fgets(char * __restrict, int, FILE *);
-#if defined(_DARWIN_UNLIMITED_STREAMS) || defined(_DARWIN_C_SOURCE)
-#else /* !_DARWIN_UNLIMITED_STREAMS && !_DARWIN_C_SOURCE */
-FILE	*fopen(const char * __restrict __filename, const char * __restrict __mode) __DARWIN_ALIAS_STARTING(__MAC_10_6, __IPHONE_2_0, __DARWIN_ALIAS(fopen));
-#endif /* (DARWIN_UNLIMITED_STREAMS || _DARWIN_C_SOURCE) */
-int	 fprintf(FILE * __restrict, const char * __restrict, ...) __printflike(2, 3);
-int	 fputs(const char * __restrict, FILE * __restrict) __DARWIN_ALIAS(fputs);
-size_t	 fread(void * __restrict __ptr, size_t __size, size_t __nitems, FILE * __restrict __stream);
-FILE	*freopen(const char * __restrict, const char * __restrict,
-                 FILE * __restrict) __DARWIN_ALIAS(freopen);
-int	 fscanf(FILE * __restrict, const char * __restrict, ...) __scanflike(2, 3);
-int	 fsetpos(FILE *, const fpos_t *);
-long	 ftell(FILE *);
-size_t	 fwrite(const void * __restrict __ptr, size_t __size, size_t __nitems, FILE * __restrict __stream) __DARWIN_ALIAS(fwrite);
-int	 getc(FILE *);
-int	 getchar(void);
-char	*gets(char *);
-void	 perror(const char *) __cold;
-int	 printf(const char * __restrict, ...) __printflike(1, 2);
-int	 putc(int, FILE *);
-int	 putchar(int);
-int	 puts(const char *);
-int	 remove(const char *);
-int	 rename (const char *__old, const char *__new);
-void	 rewind(FILE *);
-int	 scanf(const char * __restrict, ...) __scanflike(1, 2);
-void	 setbuf(FILE * __restrict, char * __restrict);
-int	 setvbuf(FILE * __restrict, char * __restrict, int, size_t);
-int	 sprintf(char * __restrict, const char * __restrict, ...) __printflike(2, 3) __swift_unavailable("Use snprintf instead.");
-int	 sscanf(const char * __restrict, const char * __restrict, ...) __scanflike(2, 3);
-FILE	*tmpfile(void);
-
-__swift_unavailable("Use mkstemp(3) instead.")
-#if !defined(_POSIX_C_SOURCE)
-__deprecated_msg("This function is provided for compatibility reasons only.  Due to security concerns inherent in the design of tmpnam(3), it is highly recommended that you use mkstemp(3) instead.")
-#endif
-char	*tmpnam(char *);
-int	 ungetc(int, FILE *);
-int	 vfprintf(FILE * __restrict, const char * __restrict, va_list) __printflike(2, 0);
-int	 vprintf(const char * __restrict, va_list) __printflike(1, 0);
-int	 vsprintf(char * __restrict, const char * __restrict, va_list) __printflike(2, 0) __swift_unavailable("Use vsnprintf instead.");
-__END_DECLS
-
-
-
-/* Additional functionality provided by:
- * POSIX.1-1988
- */
-
-#if __DARWIN_C_LEVEL >= 198808L
-#define	L_ctermid	1024	/* size for ctermid(); PATH_MAX */
-
-__BEGIN_DECLS
-#include <_ctermid.h>
-
-#if defined(_DARWIN_UNLIMITED_STREAMS) || defined(_DARWIN_C_SOURCE)
-FILE	*fdopen(int, const char *) __DARWIN_ALIAS_STARTING(__MAC_10_6, __IPHONE_3_2, __DARWIN_EXTSN(fdopen));
-#else /* !_DARWIN_UNLIMITED_STREAMS && !_DARWIN_C_SOURCE */
-FILE	*fdopen(int, const char *) __DARWIN_ALIAS_STARTING(__MAC_10_6, __IPHONE_2_0, __DARWIN_ALIAS(fdopen));
-#endif /* (DARWIN_UNLIMITED_STREAMS || _DARWIN_C_SOURCE) */
-int	 fileno(FILE *);
-__END_DECLS
-#endif /* __DARWIN_C_LEVEL >= 198808L */
-
-
-/* Additional functionality provided by:
- * POSIX.2-1992 C Language Binding Option
- */
-#if TARGET_OS_EMBEDDED
-#define __swift_unavailable_on(osx_msg, ios_msg) __swift_unavailable(ios_msg)
-#else
-#define __swift_unavailable_on(osx_msg, ios_msg) __swift_unavailable(osx_msg)
-#endif
-
-#if __DARWIN_C_LEVEL >= 199209L
-__BEGIN_DECLS
-int	 pclose(FILE *) __swift_unavailable_on("Use posix_spawn APIs or NSTask instead.", "Process spawning is unavailable.");
-#if defined(_DARWIN_UNLIMITED_STREAMS) || defined(_DARWIN_C_SOURCE)
-FILE	*popen(const char *, const char *) __DARWIN_ALIAS_STARTING(__MAC_10_6, __IPHONE_3_2, __DARWIN_EXTSN(popen)) __swift_unavailable_on("Use posix_spawn APIs or NSTask instead.", "Process spawning is unavailable.");
-#else /* !_DARWIN_UNLIMITED_STREAMS && !_DARWIN_C_SOURCE */
-FILE	*popen(const char *, const char *) __DARWIN_ALIAS_STARTING(__MAC_10_6, __IPHONE_2_0, __DARWIN_ALIAS(popen)) __swift_unavailable_on("Use posix_spawn APIs or NSTask instead.", "Process spawning is unavailable.");
-#endif /* (DARWIN_UNLIMITED_STREAMS || _DARWIN_C_SOURCE) */
-__END_DECLS
-#endif /* __DARWIN_C_LEVEL >= 199209L */
-
-#undef __swift_unavailable_on
-
-/* Additional functionality provided by:
- * POSIX.1c-1995,
- * POSIX.1i-1995,
- * and the omnibus ISO/IEC 9945-1: 1996
- */
-
-#if __DARWIN_C_LEVEL >= 199506L
-
-/* Functions internal to the implementation. */
-__BEGIN_DECLS
-int	__srget(FILE *);
-int	__svfscanf(FILE *, const char *, va_list) __scanflike(2, 0);
-int	__swbuf(int, FILE *);
-__END_DECLS
-
-/*
- * The __sfoo macros are here so that we can
- * define function versions in the C library.
- */
-#define	__sgetc(p) (--(p)->_r < 0 ? __srget(p) : (int)(*(p)->_p++))
-#if defined(__GNUC__) && defined(__STDC__)
-__header_always_inline int __sputc(int _c, FILE *_p) {
-	if (--_p->_w >= 0 || (_p->_w >= _p->_lbfsize && (char)_c != '\n'))
-		return (*_p->_p++ = _c);
-	else
-		return (__swbuf(_c, _p));
-}
-#else
-/*
- * This has been tuned to generate reasonable code on the vax using pcc.
- */
-#define	__sputc(c, p) \
-	(--(p)->_w < 0 ? \
-		(p)->_w >= (p)->_lbfsize ? \
-			(*(p)->_p = (c)), *(p)->_p != '\n' ? \
-				(int)*(p)->_p++ : \
-				__swbuf('\n', p) : \
-			__swbuf((int)(c), p) : \
-		(*(p)->_p = (c), (int)*(p)->_p++))
-#endif
-
-#define	__sfeof(p)	(((p)->_flags & __SEOF) != 0)
-#define	__sferror(p)	(((p)->_flags & __SERR) != 0)
-#define	__sclearerr(p)	((void)((p)->_flags &= ~(__SERR|__SEOF)))
-#define	__sfileno(p)	((p)->_file)
-
-__BEGIN_DECLS
-void	 flockfile(FILE *);
-int	 ftrylockfile(FILE *);
-void	 funlockfile(FILE *);
-int	 getc_unlocked(FILE *);
-int	 getchar_unlocked(void);
-int	 putc_unlocked(int, FILE *);
-int	 putchar_unlocked(int);
-
-/* Removed in Issue 6 */
-#if !defined(_POSIX_C_SOURCE) || _POSIX_C_SOURCE < 200112L
-int	 getw(FILE *);
-int	 putw(int, FILE *);
-#endif
-
-__swift_unavailable("Use mkstemp(3) instead.")
-#if !defined(_POSIX_C_SOURCE)
-__deprecated_msg("This function is provided for compatibility reasons only.  Due to security concerns inherent in the design of tempnam(3), it is highly recommended that you use mkstemp(3) instead.")
-#endif
-char	*tempnam(const char *__dir, const char *__prefix) __DARWIN_ALIAS(tempnam);
-__END_DECLS
-
-#ifndef lint
-#define	getc_unlocked(fp)	__sgetc(fp)
-#define putc_unlocked(x, fp)	__sputc(x, fp)
-#endif /* lint */
-
-#define	getchar_unlocked()	getc_unlocked(stdin)
-#define	putchar_unlocked(x)	putc_unlocked(x, stdout)
-#endif /* __DARWIN_C_LEVEL >= 199506L */
-
-
-
-/* Additional functionality provided by:
- * POSIX.1-2001
- * ISO C99
- */
-
-#if __DARWIN_C_LEVEL >= 200112L
-#include <sys/_types/_off_t.h>
-
-__BEGIN_DECLS
-int	 fseeko(FILE * __stream, off_t __offset, int __whence);
-off_t	 ftello(FILE * __stream);
-__END_DECLS
-#endif /* __DARWIN_C_LEVEL >= 200112L */
-
-#if __DARWIN_C_LEVEL >= 200112L || defined(_C99_SOURCE) || defined(__cplusplus)
-__BEGIN_DECLS
-int	 snprintf(char * __restrict __str, size_t __size, const char * __restrict __format, ...) __printflike(3, 4);
-int	 vfscanf(FILE * __restrict __stream, const char * __restrict __format, va_list) __scanflike(2, 0);
-int	 vscanf(const char * __restrict __format, va_list) __scanflike(1, 0);
-int	 vsnprintf(char * __restrict __str, size_t __size, const char * __restrict __format, va_list) __printflike(3, 0);
-int	 vsscanf(const char * __restrict __str, const char * __restrict __format, va_list) __scanflike(2, 0);
-__END_DECLS
-#endif /* __DARWIN_C_LEVEL >= 200112L || defined(_C99_SOURCE) || defined(__cplusplus) */
-
-
-
-/* Additional functionality provided by:
- * POSIX.1-2008
- */
-
-#if __DARWIN_C_LEVEL >= 200809L
-#include <sys/_types/_ssize_t.h>
-
-__BEGIN_DECLS
-int	dprintf(int, const char * __restrict, ...) __printflike(2, 3) __OSX_AVAILABLE_STARTING(__MAC_10_7, __IPHONE_4_3);
-int	vdprintf(int, const char * __restrict, va_list) __printflike(2, 0) __OSX_AVAILABLE_STARTING(__MAC_10_7, __IPHONE_4_3);
-ssize_t getdelim(char ** __restrict __linep, size_t * __restrict __linecapp, int __delimiter, FILE * __restrict __stream) __OSX_AVAILABLE_STARTING(__MAC_10_7, __IPHONE_4_3);
-ssize_t getline(char ** __restrict __linep, size_t * __restrict __linecapp, FILE * __restrict __stream) __OSX_AVAILABLE_STARTING(__MAC_10_7, __IPHONE_4_3);
-FILE *fmemopen(void * __restrict __buf, size_t __size, const char * __restrict __mode) __API_AVAILABLE(macos(10.13), ios(11.0), tvos(11.0), watchos(4.0));
-FILE *open_memstream(char **__bufp, size_t *__sizep) __API_AVAILABLE(macos(10.13), ios(11.0), tvos(11.0), watchos(4.0));
-__END_DECLS
-#endif /* __DARWIN_C_LEVEL >= 200809L */
-
-
-
-/* Darwin extensions */
-
-#if __DARWIN_C_LEVEL >= __DARWIN_C_FULL
-__BEGIN_DECLS
-extern __const int sys_nerr;		/* perror(3) external variables */
-extern __const char *__const sys_errlist[];
-
-int	 asprintf(char ** __restrict, const char * __restrict, ...) __printflike(2, 3);
-char	*ctermid_r(char *);
-char	*fgetln(FILE *, size_t *);
-__const char *fmtcheck(const char *, const char *);
-int	 fpurge(FILE *);
-void	 setbuffer(FILE *, char *, int);
-int	 setlinebuf(FILE *);
-int	 vasprintf(char ** __restrict, const char * __restrict, va_list) __printflike(2, 0);
-FILE	*zopen(const char *, const char *, int);
-
-
-/*
- * Stdio function-access interface.
- */
-FILE	*funopen(const void *,
-                 int (* _Nullable)(void *, char *, int),
-                 int (* _Nullable)(void *, const char *, int),
-                 fpos_t (* _Nullable)(void *, fpos_t, int),
-                 int (* _Nullable)(void *));
-__END_DECLS
-#define	fropen(cookie, fn) funopen(cookie, fn, 0, 0, 0)
-#define	fwopen(cookie, fn) funopen(cookie, 0, fn, 0, 0)
-
-#define	feof_unlocked(p)	__sfeof(p)
-#define	ferror_unlocked(p)	__sferror(p)
-#define	clearerr_unlocked(p)	__sclearerr(p)
-#define	fileno_unlocked(p)	__sfileno(p)
-
-#endif /* __DARWIN_C_LEVEL >= __DARWIN_C_FULL */
-
-
-#ifdef _USE_EXTENDED_LOCALES_
-#include <xlocale/_stdio.h>
-#endif /* _USE_EXTENDED_LOCALES_ */
-
-#if defined (__GNUC__) && _FORTIFY_SOURCE > 0 && !defined (__cplusplus)
-/* Security checking functions.  */
-#include <secure/_stdio.h>
-#endif
-
-#endif /* _STDIO_H_ */
-*/
\ No newline at end of file
diff --git a/lib/std/mem.c3 b/lib/std/mem.c3
index e2ea38c28..2995b9b09 100644
--- a/lib/std/mem.c3
+++ b/lib/std/mem.c3
@@ -66,19 +66,21 @@ enum AllocationKind
     CALLOC,
     REALLOC,
     FREE,
+    RESET,
 }
 
 fault AllocationFailure
 {
-    OUT_OF_MEMORY
+    OUT_OF_MEMORY,
+    UNSUPPORTED_OPERATION,
 }
 
-private tlocal Allocator thread_allocator = { SYSTEM_ALLOCATOR, null };
+private tlocal Allocator thread_allocator = { null, SYSTEM_ALLOCATOR };
 
 struct Allocator
 {
+    void* data;
     AllocatorFunction function;
-    void *data;
 }
 
 macro malloc($Type)
@@ -86,6 +88,11 @@ macro malloc($Type)
     return ($Type*)(mem::alloc($Type.sizeof));
 }
 
+fn char[] alloc_bytes(usize bytes) @inline
+{
+	return ((char*)thread_allocator.alloc(bytes, 1))[0..bytes - 1]!!;
+}
+
 /**
  * @require !alignment || @math::is_power_of_2(alignment)
  */
@@ -140,6 +147,9 @@ fn void free(void* ptr)
 	return thread_allocator.free(ptr)!!;
 }
 
+/**
+ * Run with a specific allocator inside of the macro body.
+ **/
 macro void with_allocator(Allocator allocator; @body())
 {
 	Allocator old_allocator = thread_allocator;
@@ -150,6 +160,50 @@ macro void with_allocator(Allocator allocator; @body())
 
 fn void*! talloc(usize size)
 {
-    return default_allocator.alloc(size);
+    return temp_allocator.alloc(size);
 }
 
+struct MemoryArena
+{
+	void* memory;
+	usize total;
+	usize used;
+}
+
+/**
+ * @require alignment > 0 `alignment must be non zero`
+ * @require @math::is_power_of_2(alignment)
+ * @require size > 0
+ * @require alignment <= MAX_MEMORY_ALIGNMENT `alignment too big`
+ * @require this != null
+ **/
+fn void*! MemoryArena.alloc(MemoryArena* this, usize size, usize alignment, usize prefixed_bytes = 0)
+{
+	void* start_mem = this.memory;
+	void* unaligned_pointer = start_mem + this.used + prefixed_bytes;
+	if ((uptr)unaligned_pointer < (uptr)start_mem) return AllocationFailure.OUT_OF_MEMORY!;
+	usize offset_start = aligned_offset((usize)(uptr)unaligned_pointer, alignment) - (usize)(uptr)start_mem;
+	usize end = offset_start + size;
+	if (end > this.total || end < offset_start) return AllocationFailure.OUT_OF_MEMORY!;
+	this.used = end;
+	return start_mem + offset_start;
+}
+
+/**
+ * Initialize a memory arena for use using the provided bytes.
+ *
+ * @require this != null
+ **/
+fn void MemoryArena.init(MemoryArena* this, char[] data)
+{
+	this.memory = data.ptr;
+	this.total = data.len;
+	this.used = 0;
+}
+/**
+ * @require this != null
+ **/
+fn void MemoryArena.reset(MemoryArena* this)
+{
+	this.used = 0;
+}
\ No newline at end of file
diff --git a/lib/std/mem_allocator.c3 b/lib/std/mem_allocator.c3
index faa02252d..89b865cd9 100644
--- a/lib/std/mem_allocator.c3
+++ b/lib/std/mem_allocator.c3
@@ -1,10 +1,13 @@
 module std::mem;
 
-define AllocatorFunction = fn void*!(void *data, usize new_size, usize alignment, void* old_pointer, AllocationKind kind);
+define AllocatorFunction = fn void*!(void* alloc_data, usize new_size, usize alignment, void* old_pointer, AllocationKind kind);
 
+const MAX_MEMORY_ALIGNMENT = 0x1000_0000;
 const DEFAULT_MEM_ALIGNMENT = $alignof(void*) * 2;
+const DEFAULT_SIZE_PREFIX = usize.sizeof;
+const DEFAULT_SIZE_PREFIX_ALIGNMENT = $alignof(usize);
 
-Allocator main_allocator = { SYSTEM_ALLOCATOR, null };
+Allocator main_allocator = { null, SYSTEM_ALLOCATOR };
 
 const AllocatorFunction NULL_ALLOCATOR = &null_allocator_fn;
 const AllocatorFunction SYSTEM_ALLOCATOR = &libc_allocator_fn;
@@ -38,243 +41,315 @@ fn void! Allocator.free(Allocator *allocator, void* old_pointer) @inline
 	allocator.function(allocator.data, 0, 0, old_pointer, FREE)?;
 }
 
-
-struct ArenaAllocator
+fn void Allocator.reset(Allocator *allocator)
 {
-	void* memory;
-	void* last_ptr;
-	usize total;
-	usize used;
+	allocator.function(allocator.data, 0, 0, null, RESET)!!;
 }
 
-macro void*! allocator_to_function($Type, void* data, usize new_size, usize alignment, void* old_pointer, AllocationKind kind)
+
+fn Allocator arena_allocator(MemoryArena *arena)
 {
-	$Type* allocator = data;
+	return { arena, &arena_allocator_function };
+}
+
+fn Allocator dynamic_arena_allocator(DynamicArenaAllocator* allocator)
+{
+	return { allocator, &dynamic_arena_allocator_function };
+}
+
+
+private fn usize alignment_for_allocation(usize alignment) @inline
+{
+	if (alignment < DEFAULT_MEM_ALIGNMENT)
+	{
+		alignment = DEFAULT_SIZE_PREFIX_ALIGNMENT;
+	}
+	return alignment;
+}
+
+/**
+ * @require !alignment || @math::is_power_of_2(alignment)
+ * @require data `unexpectedly missing the allocator`
+ */
+fn void*! arena_allocator_function(void* data, usize size, usize alignment, void* old_pointer, AllocationKind kind)
+{
+	MemoryArena* arena = data;
 	switch (kind)
 	{
-		case ALLOC:
-			return allocator.alloc(new_size, alignment) @inline;
 		case CALLOC:
-			return allocator.calloc(new_size, alignment) @inline;
+		case ALLOC:
+			assert(!old_pointer, "Unexpected old pointer for alloc.");
+			if (!size) return null;
+			alignment = alignment_for_allocation(alignment);
+			void* mem = arena.alloc(size, alignment, DEFAULT_SIZE_PREFIX)?;
+			*(usize*)(mem - DEFAULT_SIZE_PREFIX) = size;
+			if (kind == AllocationKind.CALLOC) mem::set(mem, 0, size);
+        	return mem;
 		case REALLOC:
-			return allocator.realloc(old_pointer, new_size, alignment) @inline;
+			if (!size) nextcase FREE;
+			if (!old_pointer) nextcase ALLOC;
+			assert((uptr)old_pointer >= (uptr)arena.memory, "Pointer originates from a different allocator.");
+			if (size > arena.total) return AllocationFailure.OUT_OF_MEMORY!;
+			alignment = alignment_for_allocation(alignment);
+			usize* old_size_ptr = (usize*)(old_pointer - DEFAULT_SIZE_PREFIX);
+			usize old_size = *old_size_ptr;
+			// Do last allocation and alignment match?
+			if (arena.memory + arena.used  == old_pointer + old_size && ptr_is_aligned(old_pointer, alignment))
+			{
+				if (old_size >= size)
+				{
+					*old_size_ptr = size;
+					arena.used -= old_size - size;
+					return old_pointer;
+				}
+				usize new_used = arena.used + size - old_size;
+				if (new_used > arena.total) return AllocationFailure.OUT_OF_MEMORY!;
+				arena.used = new_used;
+				*old_size_ptr = size;
+				return old_pointer;
+			}
+			// Otherwise just allocate new memory.
+			void* mem = arena.alloc(size, alignment, DEFAULT_SIZE_PREFIX)?;
+			*(usize*)(mem - DEFAULT_SIZE_PREFIX) = size;
+			copy(mem, old_pointer, old_size);
+			return mem;
 		case FREE:
-			allocator.free(old_pointer) @inline?;
+			if (!old_pointer) return null;
+			assert((uptr)old_pointer >= (uptr)arena.memory, "Pointer originates from a different allocator.");
+			usize old_size = *(usize*)(old_pointer - DEFAULT_SIZE_PREFIX);
+			if (old_pointer + old_size == arena.memory + arena.used)
+        	{
+        		arena.used -= old_size;
+        	}
+        	return null;
+		case RESET:
+			arena.used = 0;
 			return null;
 	}
 	@unreachable();
 }
 
-fn void*! arena_allocator_function(void* allocator, usize new_size, usize alignment, void* old_pointer, AllocationKind kind)
+struct DynamicArenaAllocator
 {
-	return @allocator_to_function(ArenaAllocator, allocator, new_size, alignment, old_pointer, kind);
+	Allocator backing_allocator;
+	DynamicArenaPage* page;
+	DynamicArenaPage* unused_page;
+	usize page_size;
 }
 
-fn Allocator ArenaAllocator.to_allocator(ArenaAllocator* allocator) @inline
-{
-	return { &arena_allocator_function, allocator };
-}
-
-
-/**
- * @require !alignment || @math::is_power_of_2(alignment)
- */
-fn void*! ArenaAllocator.alloc(ArenaAllocator* allocator, usize bytes, usize alignment = 0)
-{
-	if (!bytes) return null;
-	if (!alignment) alignment = DEFAULT_MEM_ALIGNMENT;
-	iptr next = aligned_offset((iptr)allocator.memory + allocator.used, alignment);
-	usize next_after = next - (iptr)allocator.memory + bytes;
-	if (next_after > allocator.total) return AllocationFailure.OUT_OF_MEMORY!;
-	allocator.used = next_after;
-	return allocator.last_ptr = (void*)next;
-}
-
-fn void*! ArenaAllocator.calloc(ArenaAllocator* allocator, usize bytes, usize alignment = 0)
-{
-	char* bits = allocator.alloc(bytes) @inline?;
-	mem::set(bits, 0, bytes);
-	return bits;
-}
-
-/**
- * @require ptr != null
- * @require allocator != null
- **/
-fn void*! ArenaAllocator.realloc(ArenaAllocator* allocator, void *ptr, usize bytes, usize alignment = 0)
-{
-	if (!ptr) return allocator.alloc(bytes, alignment);
-	if (!alignment) alignment = DEFAULT_MEM_ALIGNMENT;
-
-	// Is last allocation and alignment matches?
-	if (allocator.last_ptr == ptr && ptr_is_aligned(ptr, alignment))
-	{
-		usize new_used = (usize)(ptr - allocator.memory) + bytes;
-		if (new_used > allocator.total) return AllocationFailure.OUT_OF_MEMORY!;
-		allocator.used = new_used;
-		return ptr;
-	}
-
-	// Otherwise just allocate new memory.
-	void* new_mem = allocator.alloc(bytes, alignment)?;
-	// And copy too much probably!
-	copy(new_mem, ptr, (new_mem - ptr) > bytes ? bytes : (usize)(new_mem - ptr));
-	return new_mem;
-}
-
-fn void! ArenaAllocator.free(ArenaAllocator* allocator, void* ptr)
-{
-	if (!ptr) return;
-	if (ptr == allocator.last_ptr)
-	{
-		allocator.used = (usize)(ptr - allocator.memory);
-		allocator.last_ptr = null;
-		return;
-	}
-}
-
-fn void! ArenaAllocator.init(ArenaAllocator* allocator, usize arena_size)
-{
-	allocator.memory = alloc_checked(arena_size)?;
-	allocator.total = arena_size;
-	allocator.used = 0;
-	allocator.last_ptr = null;
-}
-
-fn void ArenaAllocator.reset(ArenaAllocator* allocator)
-{
-	allocator.used = 0;
-	allocator.last_ptr = null;
-}
-
-fn void ArenaAllocator.destroy(ArenaAllocator* allocator)
-{
-	assert(allocator.memory);
-	free(allocator.memory);
-	allocator.total = allocator.used = 0;
-}
-
-
 private struct DynamicArenaPage
 {
 	void* memory;
 	void* prev_arena;
 	usize total;
 	usize used;
+	void* last_ptr;
 }
 
-struct DynamicArenaAllocator
+
+/**
+ * @require !alignment || @math::is_power_of_2(alignment)
+ * @require data `unexpectedly missing the allocator`
+ */
+fn void*! dynamic_arena_allocator_function(void* data, usize size, usize alignment, void* old_pointer, AllocationKind kind)
 {
-	DynamicArenaPage* page;
-	usize total;
-	usize used;
-	usize page_size;
-	Allocator allocator;
+	DynamicArenaAllocator* allocator = data;
+	switch (kind)
+	{
+		case CALLOC:
+			assert(!old_pointer, "Unexpected no old pointer for calloc.");
+			if (!size) return null;
+			void* mem = allocator.alloc(size, alignment)?;
+			set(mem, 0, size);
+			return mem;
+		case ALLOC:
+			assert(!old_pointer, "Unexpected no old pointer for alloc.");
+			if (!size) return null;
+			return allocator.alloc(size, alignment);
+		case REALLOC:
+			if (!size)
+			{
+				if (!old_pointer) return null;
+				allocator.free(old_pointer);
+				return null;
+			}
+			if (!old_pointer) return allocator.alloc(size, alignment);
+			void* mem = allocator.realloc(old_pointer, size, alignment)?;
+			return mem;
+		case FREE:
+			if (!old_pointer) return null;
+			allocator.free(old_pointer);
+			return null;
+		case RESET:
+			allocator.reset();
+			return null;
+	}
+	@unreachable();
 }
 
-fn void DynamicArenaAllocator.init(DynamicArenaAllocator* this, usize page_size, Allocator allocator = { null, null })
+/**
+ * @require page_size >= 128
+ * @require this != null
+ **/
+fn void DynamicArenaAllocator.init(DynamicArenaAllocator* this, usize page_size, Allocator* backing_allocator = null)
 {
 	this.page = null;
-	this.used = this.total = 0;
+	this.unused_page = null;
 	this.page_size = page_size;
-	this.allocator = allocator.function ? allocator : thread_allocator;
+	this.backing_allocator = backing_allocator ? *backing_allocator : main_allocator;
 }
 
-fn void! DynamicArenaAllocator.reset(DynamicArenaAllocator* this)
+/**
+ * @require this != null
+ **/
+fn void DynamicArenaAllocator.destroy(DynamicArenaAllocator* this)
 {
 	DynamicArenaPage* page = this.page;
-	Allocator allocator = this.allocator;
-	while (page && page.prev_arena)
+	while (page)
 	{
 		DynamicArenaPage* next_page = page.prev_arena;
-		void* mem = page.memory;
-		allocator.free(page)?;
-		allocator.free(mem)?;
+		this.backing_allocator.free(page);
+		page = next_page;
+	}
+	page = this.unused_page;
+	while (page)
+	{
+		DynamicArenaPage* next_page = page.prev_arena;
+		this.backing_allocator.free(page);
 		page = next_page;
 	}
-	this.page = page;
-}
-
-fn void*! dynamic_arena_allocator_function(void* allocator, usize new_size, usize alignment, void* old_pointer, AllocationKind kind)
-{
-	return @allocator_to_function(DynamicArenaAllocator, allocator, new_size, alignment, old_pointer, kind);
-}
-
-fn Allocator DynamicArenaAllocator.to_allocator(DynamicArenaAllocator* this)
-{
-	return { &dynamic_arena_allocator_function, this };
-}
-
-fn void! DynamicArenaAllocator.destroy(DynamicArenaAllocator* this)
-{
-	this.reset();
-	DynamicArenaPage* first_page = this.page;
-	if (!first_page) return;
-	void* mem = first_page.memory;
-	this.allocator.free(this.page)?;
 	this.page = null;
-	this.allocator.free(mem)?;
+	this.unused_page = null;
 }
 
-fn void! DynamicArenaAllocator.free(DynamicArenaAllocator* allocator, void* ptr)
+/**
+ * @require ptr && this
+ * @require this.page `tried to free pointer on invalid allocator`
+ */
+private fn void DynamicArenaAllocator.free(DynamicArenaAllocator* this, void* ptr)
 {
-	// This can be made smarter.
-	return;
+	DynamicArenaPage* current_page = this.page;
+	if (ptr == current_page.last_ptr)
+	{
+		current_page.used = (usize)((ptr - DEFAULT_SIZE_PREFIX) - current_page.memory);
+	}
+	current_page.last_ptr = null;
+}
+
+/**
+ * @require old_pointer && size > 0
+ * @require this.page `tried to realloc pointer on invalid allocator`
+ */
+private fn void*! DynamicArenaAllocator.realloc(DynamicArenaAllocator* this, void* old_pointer, usize size, usize alignment)
+{
+	DynamicArenaPage* current_page = this.page;
+	alignment = alignment_for_allocation(alignment);
+	usize* old_size_ptr = old_pointer - DEFAULT_SIZE_PREFIX;
+	usize old_size = *old_size_ptr;
+	// We have the old pointer and it's correctly aligned.
+	if (old_size >= size && ptr_is_aligned(old_pointer, alignment))
+	{
+		*old_size_ptr = size;
+		if (current_page.last_ptr == old_pointer)
+		{
+			current_page.used = (usize)((old_pointer - DEFAULT_SIZE_PREFIX) - current_page.memory);
+		}
+		return old_pointer;
+	}
+	if REUSE: (current_page.last_ptr == old_pointer && ptr_is_aligned(old_pointer, alignment))
+	{
+		assert(size > old_size);
+		usize add_size = size - old_size;
+		if (add_size + current_page.used > current_page.total) break REUSE;
+		*old_size_ptr = size;
+		current_page.used += add_size;
+		return old_pointer;
+	}
+	void* new_mem = this.alloc(size, alignment)?;
+	copy(new_mem, old_pointer, old_size);
+	return new_mem;
+}
+
+private fn void DynamicArenaAllocator.reset(DynamicArenaAllocator* this)
+{
+	DynamicArenaPage* page = this.page;
+	DynamicArenaPage** unused_page_ptr = &this.unused_page;
+    while (page)
+    {
+        DynamicArenaPage* next_page = page.prev_arena;
+        page.used = 0;
+        DynamicArenaPage* prev_unused = *unused_page_ptr;
+        *unused_page_ptr = page;
+        page.prev_arena = prev_unused;
+        page = next_page;
+    }
+    this.page = page;
 }
 
 /**
  * @require @math::is_power_of_2(alignment)
+ * @require size > 0
  */
 private fn void*! DynamicArenaAllocator.alloc_new(DynamicArenaAllocator* this, usize size, usize alignment)
 {
-	usize page_size = @max(this.page_size, size);
-	void* mem = this.allocator.alloc(page_size, alignment)?;
-	DynamicArenaPage*! page = this.allocator.alloc(DynamicArenaPage.sizeof);
+	usize page_size = @max(this.page_size, size + DEFAULT_SIZE_PREFIX + alignment);
+	void* mem = this.backing_allocator.alloc(page_size)?;
+	DynamicArenaPage*! page = this.backing_allocator.alloc(DynamicArenaPage.sizeof);
 	if (catch err = page)
 	{
-		this.allocator.free(mem);
+		this.backing_allocator.free(mem);
 		return err!;
 	}
     page.memory = mem;
+    usize offset = aligned_offset((usize)mem + DEFAULT_SIZE_PREFIX, alignment) - (usize)mem;
+    usize* size_ptr = mem + offset - DEFAULT_SIZE_PREFIX;
+    *size_ptr = size;
 	page.prev_arena = this.page;
 	page.total = page_size;
-	page.used = size;
+	page.used = size + offset;
 	this.page = page;
 
-	return page.memory;
+	return page.last_ptr = page.memory + offset;
 }
 
 /**
  * @require !alignment || @math::is_power_of_2(alignment)
+ * @require size > 0
+ * @require this
  */
-fn void*! DynamicArenaAllocator.calloc(DynamicArenaAllocator* allocator, usize size, usize alignment = 0)
+private fn void*! DynamicArenaAllocator.alloc(DynamicArenaAllocator* this, usize size, usize alignment)
 {
-	void* mem = allocator.alloc(size, alignment)?;
-	set(mem, 0, size);
-	return mem;
+	alignment = alignment_for_allocation(alignment);
+	DynamicArenaPage* page = this.page;
+	if (!page && this.unused_page)
+	{
+		this.page = page = this.unused_page;
+		this.unused_page = page.prev_arena;
+		page.prev_arena = null;
+	}
+    if (!page) return this.alloc_new(size, alignment);
+    usize start = aligned_offset((uptr)page.memory + page.used + DEFAULT_SIZE_PREFIX, alignment) - (usize)page.memory;
+    usize new_used = start + size;
+    if ALLOCATE_NEW: (new_used > page.total)
+    {
+        if ((page = this.unused_page))
+        {
+            start = aligned_offset((uptr)page.memory + DEFAULT_SIZE_PREFIX, alignment) - (usize)page.memory;
+            new_used = start + size;
+            if (page.total >= new_used)
+            {
+	    		this.unused_page = page.prev_arena;
+    	    	page.prev_arena = this.page;
+    		    this.page = page;
+    		    break ALLOCATE_NEW;
+            }
+        }
+ 	    return this.alloc_new(size, alignment);
+    }
+    page.used = new_used;
+    void* mem = page.memory + start;
+    usize* size_offset = mem - DEFAULT_SIZE_PREFIX;
+    *size_offset = size;
+    return mem;
 }
 
-/**
- * @require !alignment || @math::is_power_of_2(alignment)
- */
-fn void*! DynamicArenaAllocator.realloc(DynamicArenaAllocator* allocator, void* ptr, usize size, usize alignment = 0)
-{
-	void* mem = allocator.alloc(size, alignment)?;
-	copy(mem, ptr, size);
-	return mem;
-}
-
-/**
- * @require !alignment || @math::is_power_of_2(alignment)
- */
-fn void*! DynamicArenaAllocator.alloc(DynamicArenaAllocator* this, usize size, usize alignment)
-{
-	DynamicArenaPage *page = this.page;
-	if (!alignment) alignment = DEFAULT_MEM_ALIGNMENT;
-	if (!page) return this.alloc_new(size, alignment);
-	usize start = aligned_offset((uptr)page.memory + page.used, alignment) - (usize)page.memory;
-	usize new_used = start + size;
-	if (new_used > page.total) return this.alloc_new(size, alignment);
-	page.used = new_used;
-	return page.memory + start;
-}
diff --git a/lib/std/mem_allocator_fn.c3 b/lib/std/mem_allocator_fn.c3
index 270a37000..3de78a2d3 100644
--- a/lib/std/mem_allocator_fn.c3
+++ b/lib/std/mem_allocator_fn.c3
@@ -54,6 +54,8 @@ fn void*! libc_allocator_fn(void *unused, usize bytes, usize alignment, void* ol
             }
             if (!data) return AllocationFailure.OUT_OF_MEMORY!;
             return data;
+        case RESET:
+            return AllocationFailure.UNSUPPORTED_OPERATION!;
         case FREE:
             libc::free(old_pointer);
             return null;
diff --git a/lib/std/mem_temp_allocator.c3 b/lib/std/mem_temp_allocator.c3
index 9fc258b70..bf7101d7f 100644
--- a/lib/std/mem_temp_allocator.c3
+++ b/lib/std/mem_temp_allocator.c3
@@ -6,7 +6,7 @@ const TEMP_PAGES = 64;
 private char[TEMP_BLOCK_SIZE * TEMP_PAGES] allocator_static_storage;
 private void*[TEMP_PAGES] allocator_static_page_storage;
 
-SlotAllocator default_allocator = {
+SlotAllocator temp_allocator = {
     .pages = &allocator_static_storage,
     .page_size = TEMP_BLOCK_SIZE,
     .page_count = TEMP_PAGES,
diff --git a/resources/examples/notworking/timeit.c3 b/resources/examples/notworking/timeit.c3
index 170cd9133..cd0e62ba1 100644
--- a/resources/examples/notworking/timeit.c3
+++ b/resources/examples/notworking/timeit.c3
@@ -1,13 +1,12 @@
 module test;
 import std::time;
-import std::io;
 
 public macro timeit(#call)
 {
     Time t = time::current();
     typeof(#call) result = #call;
     TimeDiff diff = time::current() - t;
-    io::printf("'%s' took %f ms\n", $stringify(#call), diff * 1000);
+    libc::printf("'%s' took %f ms\n", $stringify(#call), diff * 1000);
     return result;
 }
 
diff --git a/resources/testfragments/demo_err.c3 b/resources/testfragments/boolerr.c3
similarity index 94%
rename from resources/testfragments/demo_err.c3
rename to resources/testfragments/boolerr.c3
index c7714740a..24f8b59d9 100644
--- a/resources/testfragments/demo_err.c3
+++ b/resources/testfragments/boolerr.c3
@@ -127,11 +127,12 @@ fn char* nameFromError(anyerr e)
 fn void main()
 {
     const char[][] URLS = { "good", "title-empty", "title-missing", "head-missing", "fail" };
-    DynamicArenaAllocator allocator;
-    allocator.init(1024);
+    DynamicArenaAllocator dynamic_arena;
+	dynamic_arena.init(1024);
+    Allocator allocator = mem::dynamic_arena_allocator(&dynamic_arena);
     foreach (char[] url : URLS)
     {
-        @mem::with_allocator(allocator.to_allocator())
+        @mem::with_allocator(allocator)
         {
 	        // Yes, it's pretty onerous to print strings for the moment in C3
             libc::printf(`Checking "https://%.*s/":` "\n", (int)url.len, url.ptr);
@@ -148,5 +149,5 @@ fn void main()
         };
         allocator.reset();
     }
-    allocator.destroy();
+    dynamic_arena.destroy();
 }
diff --git a/resources/testfragments/demo_errors.c3 b/resources/testfragments/demo_errors.c3
deleted file mode 100644
index e69de29bb..000000000
diff --git a/resources/testfragments/tmem.c3 b/resources/testfragments/tmem.c3
index cbf440616..54388d0a5 100644
--- a/resources/testfragments/tmem.c3
+++ b/resources/testfragments/tmem.c3
@@ -82,5 +82,5 @@ fn void main()
     String w;
     w.init("Yo man!");
     s.concat(&w);
-    io::printf("Message was: %s\n", s.zstr());
+    libc::printf("Message was: %s\n", s.zstr());
 }
\ No newline at end of file
diff --git a/src/compiler/llvm_codegen_expr.c b/src/compiler/llvm_codegen_expr.c
index 227d09145..8ea83f77b 100644
--- a/src/compiler/llvm_codegen_expr.c
+++ b/src/compiler/llvm_codegen_expr.c
@@ -2311,6 +2311,8 @@ static void llvm_emit_slice_values(GenContext *c, Expr *slice, BEValue *parent_r
 	LLVMValueRef parent_addr = parent_addr_x.value;
 	LLVMValueRef parent_load_value = NULL;
 	LLVMValueRef parent_base;
+	bool is_failable = type_is_failable(parent_type);
+	parent_type = type_no_fail(parent_type);
 	switch (parent_type->type_kind)
 	{
 		case TYPE_POINTER:
@@ -2433,8 +2435,8 @@ static void gencontext_emit_slice(GenContext *c, BEValue *be_value, Expr *expr)
 	// Calculate the size
 	LLVMValueRef size = LLVMBuildSub(c->builder, LLVMBuildAdd(c->builder, end.value, llvm_const_int(c, start.type, 1), ""), start.value, "size");
 	LLVMValueRef start_pointer;
-
-	switch (parent.type->type_kind)
+	Type *type = type_lowering(parent.type);
+	switch (type->type_kind)
 	{
 		case TYPE_ARRAY:
 		{
@@ -2459,7 +2461,8 @@ static void gencontext_emit_slice(GenContext *c, BEValue *be_value, Expr *expr)
 	}
 
 	// Create a new subarray type
-	llvm_value_set(be_value, llvm_emit_aggregate_value(c, expr->type, start_pointer, size, NULL), expr->type);
+	Type *expr_type = type_lowering(expr->type);
+	llvm_value_set(be_value, llvm_emit_aggregate_value(c, expr_type, start_pointer, size, NULL), expr_type);
 }
 
 static void llvm_emit_slice_assign(GenContext *c, BEValue *be_value, Expr *expr)
@@ -4540,7 +4543,7 @@ void llvm_emit_builtin_call(GenContext *c, BEValue *result_value, Expr *expr)
 	llvm_emit_intrinsic_expr(c, llvm_get_intrinsic(func), result_value, expr);
 }
 
-void llvm_add_call_attributes(GenContext *c, LLVMValueRef call_value, int start_index, int count, Type **types, ABIArgInfo **infos)
+void llvm_add_abi_call_attributes(GenContext *c, LLVMValueRef call_value, int start_index, int count, Type **types, ABIArgInfo **infos)
 {
 	for (unsigned i = 0; i < count; i++)
 	{
@@ -4817,10 +4820,15 @@ void llvm_emit_call_expr(GenContext *c, BEValue *result_value, Expr *expr)
 		}
 	}
 
-	llvm_add_call_attributes(c, call_value, 1, non_variadic_params, params, abi_args);
+	llvm_add_abi_call_attributes(c, call_value, 1, non_variadic_params, params, abi_args);
 	if (prototype->abi_varargs)
 	{
-		llvm_add_call_attributes(c, call_value, 1 + non_variadic_params, vec_size(prototype->varargs), prototype->varargs, prototype->abi_varargs);
+		llvm_add_abi_call_attributes(c,
+		                             call_value,
+		                             1 + non_variadic_params,
+		                             vec_size(prototype->varargs),
+		                             prototype->varargs,
+		                             prototype->abi_varargs);
 	}
 
 	// 11. Process the return value.
@@ -4987,6 +4995,9 @@ void llvm_emit_call_expr(GenContext *c, BEValue *result_value, Expr *expr)
 		// 17f. Emit the "after" block.
 		llvm_emit_block(c, after_block);
 
+		// Emit the current stack into the thread local or things will get messed up.
+		if (c->debug.last_ptr) llvm_store(c, c->debug.last_ptr, c->debug.stack_slot, type_alloca_alignment(type_voidptr));
+
 		// 17g. If void, be_value contents should be skipped.
 		if (!prototype->ret_by_ref)
 		{
@@ -4996,9 +5007,10 @@ void llvm_emit_call_expr(GenContext *c, BEValue *result_value, Expr *expr)
 
 		// 17h. Assign the return param to be_value.
 		*result_value = synthetic_return_param;
-		if (c->debug.last_ptr) llvm_store(c, c->debug.last_ptr, c->debug.stack_slot, type_alloca_alignment(type_voidptr));
 		return;
 	}
+
+	// Emit the current stack into the thread local or things will get messed up.
 	if (c->debug.last_ptr) llvm_store(c, c->debug.last_ptr, c->debug.stack_slot, type_alloca_alignment(type_voidptr));
 
 	// 17i. The simple case here is where there is a normal return.
diff --git a/test/test_suite/compile_time/stringify.c3t b/test/test_suite/compile_time/stringify.c3t
index 75d0d3fc4..1f5bfccf3 100644
--- a/test/test_suite/compile_time/stringify.c3t
+++ b/test/test_suite/compile_time/stringify.c3t
@@ -14,7 +14,7 @@ $else:
     $Type result = #call;
 $endif;
     long diff = (long)libc::clock() - t;
-    io::printf("'%s' took %lld us\n", $stringify(#call), diff);
+    libc::printf("'%s' took %lld us\n", $stringify(#call), diff);
 $if (!$is_void):
     return result;
 $endif;
@@ -22,7 +22,7 @@ $endif;
 
 fn void test()
 {
-    for (int i = 0; i < 1000; i++) io::printf("%d\n", i);
+    for (int i = 0; i < 1000; i++) libc::printf("%d\n", i);
 }
 
 fn void main()
@@ -30,7 +30,7 @@ fn void main()
     @timeit(test());
     int a = 100;
     int x = @timeit(1 + 3 + a);
-    io::printf("Result was %d\n", x);
+    libc::printf("Result was %d\n", x);
 }
 
 /* #expect: test.ll
diff --git a/test/test_suite/errors/general_error_regression.c3t b/test/test_suite/errors/general_error_regression.c3t
index 0e8395633..a474bd8c3 100644
--- a/test/test_suite/errors/general_error_regression.c3t
+++ b/test/test_suite/errors/general_error_regression.c3t
@@ -47,22 +47,22 @@ fn void main()
     Foo ef = Foo.Y;
     anyerr x = f;
     ulong z = (ulong)(x);
-    io::printf("1: %p\n", z);
+    libc::printf("1: %p\n", z);
     x = ef;
     z = (ulong)(x);
-    io::printf("2: %p\n", z);
+    libc::printf("2: %p\n", z);
     x = Foo.W;
     z = (ulong)(x);
-    io::printf("21: %p\n", z);
+    libc::printf("21: %p\n", z);
     x = Foo.W1;
     z = (ulong)(x);
-    io::printf("22: %p\n", z);
+    libc::printf("22: %p\n", z);
     x = Foob.X1;
     z = (ulong)(x);
-    io::printf("3: %p\n", z);
+    libc::printf("3: %p\n", z);
     x = Foob.Y2;
     z = (ulong)(x);
-    io::printf("4: %p\n", z);
+    libc::printf("4: %p\n", z);
     Bar b;
     MyEnum a = MyEnum.A;
     f.hello();
diff --git a/test/test_suite/from_docs/examples_forswitch.c3t b/test/test_suite/from_docs/examples_forswitch.c3t
index 775f547d6..bf9393649 100644
--- a/test/test_suite/from_docs/examples_forswitch.c3t
+++ b/test/test_suite/from_docs/examples_forswitch.c3t
@@ -8,7 +8,7 @@ fn void example_for()
     // the for-loop is the same as C99.
     for (int i = 0; i < 10; i++)
     {
-        io::printf("%d\n", i);
+        libc::printf("%d\n", i);
     }
 
     // also equal
diff --git a/test/test_suite/from_docs/examples_if_catch.c3t b/test/test_suite/from_docs/examples_if_catch.c3t
index e85d752ec..8b574e805 100644
--- a/test/test_suite/from_docs/examples_if_catch.c3t
+++ b/test/test_suite/from_docs/examples_if_catch.c3t
@@ -32,15 +32,15 @@ fn void main()
     if (catch err = ratio)
     {
         case MathError.DIVISION_BY_ZERO:
-            io::printf("Division by zero\n");
+            libc::printf("Division by zero\n");
             return;
         default:
-            io::printf("Unexpected error!");
+            libc::printf("Unexpected error!");
             return;
     }
     // Flow typing makes "ratio"
     // have the type double here.
-    io::printf("Ratio was %f\n", ratio);
+    libc::printf("Ratio was %f\n", ratio);
 }
 
 /* #expect: demo.ll
diff --git a/test/test_suite/initializer_lists/statics.c3t b/test/test_suite/initializer_lists/statics.c3t
index b0586a0de..8335f5429 100644
--- a/test/test_suite/initializer_lists/statics.c3t
+++ b/test/test_suite/initializer_lists/statics.c3t
@@ -17,7 +17,7 @@ fn void test()
 {
     Bar[] b = { { 1, 2 } };
     static Bar[] c = { { 1, 2 } };
-    io::printf("%d %d\n", b[0].y, c[0].y);
+    libc::printf("%d %d\n", b[0].y, c[0].y);
     b[0].y += 1;
     c[0].y += 1;
 
diff --git a/test/test_suite/initializer_lists/subarrays.c3t b/test/test_suite/initializer_lists/subarrays.c3t
index 59c107740..a96d4d092 100644
--- a/test/test_suite/initializer_lists/subarrays.c3t
+++ b/test/test_suite/initializer_lists/subarrays.c3t
@@ -21,13 +21,13 @@ int* fofeo = &&(int[2]{ 3, 4 });
 fn int main()
 {
     Bar w = arrbar[1];
-    io::printf("%d\n", arrbar[1].x);
+    libc::printf("%d\n", arrbar[1].x);
     int[] x = { 1, 2, 3 };
     int* y = &&(int[3]{ 123, 234, 567 });
     io::println("Start:");
-    io::printf("X len: %d mid element %d\n", (int)(x.len), x[1]);
-    io::printf("Y mid element %d\n", y[1]);
-    io::printf("Fofeo second element %d\n", fofeo[1]);
+    libc::printf("X len: %d mid element %d\n", (int)(x.len), x[1]);
+    libc::printf("Y mid element %d\n", y[1]);
+    libc::printf("Fofeo second element %d\n", fofeo[1]);
     Baz ffe = { .x = 1 };
     int[1] azz = {};
     int[*] a = {};
diff --git a/test/test_suite/macros/macro_convert_literal.c3 b/test/test_suite/macros/macro_convert_literal.c3
index a6e41023a..d8d0ee7ab 100644
--- a/test/test_suite/macros/macro_convert_literal.c3
+++ b/test/test_suite/macros/macro_convert_literal.c3
@@ -8,5 +8,5 @@ macro foo(y)
 
 fn void main()
 {
-    io::printf("%d\n", @foo(10));
+    libc::printf("%d\n", @foo(10));
 }
\ No newline at end of file
diff --git a/test/test_suite/statements/switch_errors.c3 b/test/test_suite/statements/switch_errors.c3
index 9d4c2e0fa..f3bfdbb33 100644
--- a/test/test_suite/statements/switch_errors.c3
+++ b/test/test_suite/statements/switch_errors.c3
@@ -151,10 +151,10 @@ fn void main()
     switch (catch err = testMayError()) // #error: Catch unwrapping is only allowed
     {
         case MathError.DIVISION_BY_ZERO:
-            io::printf("Division by zero\n");
+            libc::printf("Division by zero\n");
             return;
         default:
-            io::printf("Unexpected error!");
+            libc::printf("Unexpected error!");
             return;
     }
 }
\ No newline at end of file