[wasm] use sbrk instead of emscripten mmap or malloc when loading bytes into heap (#100106)

Use sbrk to allocate persistent space for large load_bytes_into_heap calls to avoid the startup overhead of emscripten's malloc and memset for the new space

Author: kg

src/mono/browser/browser.proj

@@ -200,6 +200,7 @@
       <EmccExportedFunction Include="_free" />
       <EmccExportedFunction Include="_htons" />
       <EmccExportedFunction Include="_malloc" />
+      <EmccExportedFunction Include="_sbrk" />
       <EmccExportedFunction Include="_memalign" />
       <EmccExportedFunction Include="_memset" />
       <EmccExportedFunction Include="_ntohs" />

src/mono/browser/runtime/assets.ts

@@ -7,7 +7,7 @@ import cwraps from "./cwraps";
 import { mono_wasm_load_icu_data } from "./icu";
 import { Module, loaderHelpers, mono_assert, runtimeHelpers } from "./globals";
 import { mono_log_info, mono_log_debug, parseSymbolMapFile } from "./logging";
-import { mono_wasm_load_bytes_into_heap } from "./memory";
+import { mono_wasm_load_bytes_into_heap_persistent } from "./memory";
 import { endMeasure, MeasuredBlock, startMeasure } from "./profiler";
 import { AssetEntry } from "./types";
 import { VoidPtr } from "./types/emscripten";
@@ -37,7 +37,7 @@ export function instantiate_asset (asset: AssetEntry, url: string, bytes: Uint8A
         // falls through
         case "heap":
         case "icu":
-            offset = mono_wasm_load_bytes_into_heap(bytes);
+            offset = mono_wasm_load_bytes_into_heap_persistent(bytes);
             break;
 
         case "vfs": {

src/mono/browser/runtime/dotnet.d.ts

@@ -20,6 +20,7 @@ declare interface Int32Ptr extends NativePointer {
 declare interface EmscriptenModule {
     _malloc(size: number): VoidPtr;
     _free(ptr: VoidPtr): void;
+    _sbrk(size: number): VoidPtr;
     out(message: string): void;
     err(message: string): void;
     ccall<T>(ident: string, returnType?: string | null, argTypes?: string[], args?: any[], opts?: any): T;

src/mono/browser/runtime/memory.ts

@@ -325,7 +325,24 @@ export function withStackAlloc<T1, T2, T3, TResult> (bytesWanted: number, f: (pt
 // @bytes must be a typed array. space is allocated for it in the native heap
 //  and it is copied to that location. returns the address of the allocation.
 export function mono_wasm_load_bytes_into_heap (bytes: Uint8Array): VoidPtr {
-    const memoryOffset = Module._malloc(bytes.length);
+    // pad sizes by 16 bytes for simd
+    const memoryOffset = Module._malloc(bytes.length + 16);
+    const heapBytes = new Uint8Array(localHeapViewU8().buffer, <any>memoryOffset, bytes.length);
+    heapBytes.set(bytes);
+    return memoryOffset;
+}
+
+// @bytes must be a typed array. space is allocated for it in memory
+//  and it is copied to that location. returns the address of the data.
+// the result pointer *cannot* be freed because malloc is bypassed for speed.
+export function mono_wasm_load_bytes_into_heap_persistent (bytes: Uint8Array): VoidPtr {
+    // pad sizes by 16 bytes for simd
+    const desiredSize = bytes.length + 16;
+    // wasm memory page size is 64kb. allocations smaller than that are probably best
+    //  serviced by malloc
+    const memoryOffset = (desiredSize < (64 * 1024))
+        ? Module._malloc(desiredSize)
+        : Module._sbrk(desiredSize);
     const heapBytes = new Uint8Array(localHeapViewU8().buffer, <any>memoryOffset, bytes.length);
     heapBytes.set(bytes);
     return memoryOffset;

src/mono/browser/runtime/types/emscripten.ts

@@ -26,6 +26,7 @@ export declare interface EmscriptenModule {
     // this should match emcc -s EXPORTED_FUNCTIONS
     _malloc(size: number): VoidPtr;
     _free(ptr: VoidPtr): void;
+    _sbrk(size: number): VoidPtr;
 
     // this should match emcc -s EXPORTED_RUNTIME_METHODS
     out(message: string): void;