Apply the sbrk/brk value at compile time (#2366)

We've had an option to set the location of the sbrk ptr, but not the value.
Applying the value as well is necessary for standalone wasm, as otherwise we set
it in JS.

1 files changed, 16 insertions, 2 deletions

diff --git a/src/ir/memory-utils.h b/src/ir/memory-utils.h
index fd4b865f4..39914a95a 100644
--- a/src/ir/memory-utils.h
+++ b/src/ir/memory-utils.h
@@ -22,17 +22,31 @@
 
 #include "literal.h"
 #include "wasm-binary.h"
+#include "wasm-builder.h"
 #include "wasm.h"
 
 namespace wasm {
 
 namespace MemoryUtils {
-// flattens memory into a single data segment. returns true if successful
-inline bool flatten(Memory& memory) {
+// Flattens memory into a single data segment, or no segment. If there is
+// a segment, it starts at 0.
+// If ensuredSegmentSize is provided, then a segment is always emitted,
+// and of at least that size.
+// Returns true if successful (e.g. relocatable segments cannot be flattened).
+inline bool flatten(Memory& memory,
+                    Index ensuredSegmentSize = 0,
+                    Module* module = nullptr) {
   if (memory.segments.size() == 0) {
+    if (ensuredSegmentSize > 0) {
+      assert(module); // must provide a module if ensuring a size.
+      Builder builder(*module);
+      memory.segments.emplace_back(builder.makeConst(Literal(int32_t(0))));
+      memory.segments[0].data.resize(ensuredSegmentSize);
+    }
     return true;
   }
   std::vector<char> data;
+  data.resize(ensuredSegmentSize);
   for (auto& segment : memory.segments) {
     if (segment.isPassive) {
       return false;