[NFC] Encapsulate source map reader state (#7132)

Move all state relevant to reading source maps out of WasmBinaryReader
and into a new utility, SourceMapReader. This is a prerequisite for
parallelizing the parsing of function bodies, since the source map
reader state is different at the beginning of each function.

Also take the opportunity to simplify the way we read source maps, for
example by deferring the reading of anything but the position of a debug
location until it will be used and by using `std::optional` instead of
singleton `std::set`s to store function prologue and epilogue debug
locations.

1 files changed, 4 insertions, 4 deletions

diff --git a/src/wasm-stack.h b/src/wasm-stack.h
index 85003f9ea..f48233333 100644
--- a/src/wasm-stack.h
+++ b/src/wasm-stack.h
@@ -456,8 +456,8 @@ public:
 
   void emit(Expression* curr) { writer.visit(curr); }
   void emitHeader() {
-    if (func->prologLocation.size()) {
-      parent.writeDebugLocation(*func->prologLocation.begin());
+    if (func->prologLocation) {
+      parent.writeDebugLocation(*func->prologLocation);
     }
     writer.mapLocalsAndEmitHeader();
   }
@@ -469,8 +469,8 @@ public:
   void emitFunctionEnd() {
     // Indicate the debug location corresponding to the end opcode
     // that terminates the function code.
-    if (func->epilogLocation.size()) {
-      parent.writeDebugLocation(*func->epilogLocation.begin());
+    if (func->epilogLocation) {
+      parent.writeDebugLocation(*func->epilogLocation);
     } else {
       // The end opcode has no debug location.
       parent.writeNoDebugLocation();