1 files changed, 114 insertions, 0 deletions
diff --git a/v_windows/v/vlib/builtin/prealloc.c.v b/v_windows/v/vlib/builtin/prealloc.c.v
new file mode 100644
index 0000000..0ef66fc
--- /dev/null
+++ b/v_windows/v/vlib/builtin/prealloc.c.v
@@ -0,0 +1,114 @@
+module builtin
+
+// With -prealloc, V calls libc's malloc to get chunks, each at least 16MB
+// in size, as needed. Once a chunk is available, all malloc() calls within
+// V code, that can fit inside the chunk, will use it instead, each bumping a
+// pointer, till the chunk is filled. Once a chunk is filled, a new chunk will
+// be allocated by calling libc's malloc, and the process continues.
+// Each new chunk has a pointer to the old one, and at the end of the program,
+// the entire linked list of chunks is freed.
+// The goal of all this is to amortize the cost of calling libc's malloc,
+// trading higher memory usage for a compiler (or any single threaded batch
+// mode program), for a ~8-10% speed increase.
+// NB: `-prealloc` is NOT safe to be used for multithreaded programs!
+
+// size of the preallocated chunk
+const prealloc_block_size = 16 * 1024 * 1024
+
+__global g_memory_block &VMemoryBlock
+[heap]
+struct VMemoryBlock {
+mut:
+	id        int
+	cap       int
+	start     &byte = 0
+	previous  &VMemoryBlock = 0
+	remaining int
+	current   &byte = 0
+	mallocs   int
+}
+
+[unsafe]
+fn vmemory_block_new(prev &VMemoryBlock, at_least int) &VMemoryBlock {
+	mut v := unsafe { &VMemoryBlock(C.calloc(1, sizeof(VMemoryBlock))) }
+	if prev != 0 {
+		v.id = prev.id + 1
+	}
+	v.previous = prev
+	block_size := if at_least < prealloc_block_size { prealloc_block_size } else { at_least }
+	v.start = unsafe { C.malloc(block_size) }
+	v.cap = block_size
+	v.remaining = block_size
+	v.current = v.start
+	return v
+}
+
+[unsafe]
+fn vmemory_block_malloc(n int) &byte {
+	unsafe {
+		if g_memory_block.remaining < n {
+			g_memory_block = vmemory_block_new(g_memory_block, n)
+		}
+		mut res := &byte(0)
+		res = g_memory_block.current
+		g_memory_block.remaining -= n
+		g_memory_block.mallocs++
+		g_memory_block.current += n
+		return res
+	}
+}
+
+/////////////////////////////////////////////////
+
+[unsafe]
+fn prealloc_vinit() {
+	unsafe {
+		g_memory_block = vmemory_block_new(voidptr(0), prealloc_block_size)
+		$if !freestanding {
+			C.atexit(prealloc_vcleanup)
+		}
+	}
+}
+
+[unsafe]
+fn prealloc_vcleanup() {
+	$if prealloc_stats ? {
+		// NB: we do 2 loops here, because string interpolation
+		// in the first loop may still use g_memory_block
+		// The second loop however should *not* allocate at all.
+		mut nr_mallocs := i64(0)
+		mut mb := g_memory_block
+		for mb != 0 {
+			nr_mallocs += mb.mallocs
+			eprintln('> freeing mb.id: ${mb.id:3} | cap: ${mb.cap:7} | rem: ${mb.remaining:7} | start: ${voidptr(mb.start)} | current: ${voidptr(mb.current)} | diff: ${u64(mb.current) - u64(mb.start):7} bytes | mallocs: $mb.mallocs')
+			mb = mb.previous
+		}
+		eprintln('> nr_mallocs: $nr_mallocs')
+	}
+	unsafe {
+		for g_memory_block != 0 {
+			C.free(g_memory_block.start)
+			g_memory_block = g_memory_block.previous
+		}
+	}
+}
+
+[unsafe]
+fn prealloc_malloc(n int) &byte {
+	return unsafe { vmemory_block_malloc(n) }
+}
+
+[unsafe]
+fn prealloc_realloc(old_data &byte, old_size int, new_size int) &byte {
+	new_ptr := unsafe { vmemory_block_malloc(new_size) }
+	min_size := if old_size < new_size { old_size } else { new_size }
+	unsafe { C.memcpy(new_ptr, old_data, min_size) }
+	return new_ptr
+}
+
+[unsafe]
+fn prealloc_calloc(n int) &byte {
+	new_ptr := unsafe { vmemory_block_malloc(n) }
+	unsafe { C.memset(new_ptr, 0, n) }
+	return new_ptr
+}