Preserve debug info through the optimizer (#981)

* add debugInfo option to passes, and use it to keep debug info alive through optimizations when we need it

* add fib testcase for debug info

* when preserving debug info, do not move code around call-imports, so debug info intrinsics remain stationary

* improve wasm-module-building handling of the single-threaded case: don't create workers, which is more efficient and also nicer for debugging

* process debug info in a more precise way, reordering it from being after the node (as it was a comment in JS) to before the node

* remove unreachable hack for debug info, which is no longer needed since we reorder them, and make sure to finalize blocks in which we reorder

1 files changed, 10 insertions, 1 deletions

diff --git a/src/ast_utils.h b/src/ast_utils.h
index 00b755bf7..17627d959 100644
--- a/src/ast_utils.h
+++ b/src/ast_utils.h
@@ -73,10 +73,12 @@ struct BreakSeeker : public PostWalker<BreakSeeker> {
 struct EffectAnalyzer : public PostWalker<EffectAnalyzer> {
   EffectAnalyzer(PassOptions& passOptions, Expression *ast = nullptr) {
     ignoreImplicitTraps = passOptions.ignoreImplicitTraps;
+    debugInfo = passOptions.debugInfo;
     if (ast) analyze(ast);
   }
 
   bool ignoreImplicitTraps;
+  bool debugInfo;
 
   void analyze(Expression *ast) {
     breakNames.clear();
@@ -187,7 +189,14 @@ struct EffectAnalyzer : public PostWalker<EffectAnalyzer> {
   }
 
   void visitCall(Call *curr) { calls = true; }
-  void visitCallImport(CallImport *curr) { calls = true; }
+  void visitCallImport(CallImport *curr) {
+    calls = true;
+    if (debugInfo) {
+      // debugInfo call imports must be preserved very strongly, do not
+      // move code around them
+      branches = true; // !
+    }
+  }
   void visitCallIndirect(CallIndirect *curr) { calls = true; }
   void visitGetLocal(GetLocal *curr) {
     localsRead.insert(curr->index);