Optimize normally with debug info (#1927)

* optimize normally with debug info - some of it may be removed, but that's the price of higher optimization levels, and by optimizing normally in profiling and -g2 etc. builds they are more comparable to normal ones, yielding better data
* copy debug locations automatically in replaceCurrent in wasm-traversal, so optimization passes at least by default will preserve debuggability

2 files changed, 20 insertions, 11 deletions

diff --git a/src/passes/pass.cpp b/src/passes/pass.cpp
index 4b14186fb..58a5f2f0a 100644
--- a/src/passes/pass.cpp
+++ b/src/passes/pass.cpp
@@ -156,9 +156,7 @@ void PassRunner::addDefaultFunctionOptimizationPasses() {
     add("flatten");
     add("local-cse");
   }
-  if (!options.debugInfo) { // debug info must be preserved, do not dce it
-    add("dce");
-  }
+  add("dce");
   add("remove-unused-brs");
   add("remove-unused-names");
   add("optimize-instructions");
@@ -215,14 +213,12 @@ void PassRunner::addDefaultGlobalOptimizationPrePasses() {
 
 void PassRunner::addDefaultGlobalOptimizationPostPasses() {
   // inlining/dae+optimizing can remove debug annotations
-  if (!options.debugInfo) {
-    if (options.optimizeLevel >= 2 || options.shrinkLevel >= 1) {
-      add("dae-optimizing");
-    }
-    // inline when working hard, and when not preserving debug info
-    if (options.optimizeLevel >= 2 || options.shrinkLevel >= 2) {
-      add("inlining-optimizing");
-    }
+  if (options.optimizeLevel >= 2 || options.shrinkLevel >= 1) {
+    add("dae-optimizing");
+  }
+  // inline when working hard, and when not preserving debug info
+  if (options.optimizeLevel >= 2 || options.shrinkLevel >= 2) {
+    add("inlining-optimizing");
   }
   add("duplicate-function-elimination"); // optimizations show more functions as duplicate
   add("remove-unused-module-elements");
diff --git a/src/wasm-traversal.h b/src/wasm-traversal.h
index 5bd316d89..541490418 100644
--- a/src/wasm-traversal.h
+++ b/src/wasm-traversal.h
@@ -302,6 +302,19 @@ struct Walker : public VisitorType {
   // just one visit*() method is called by the traversal; if you replace a node,
   // and you want to process the output, you must do that explicitly).
   Expression* replaceCurrent(Expression* expression) {
+    // Copy debug info, if present.
+    if (currFunction) {
+      auto& debugLocations = currFunction->debugLocations;
+      if (!debugLocations.empty()) {
+        auto* curr = getCurrent();
+        auto iter = debugLocations.find(curr);
+        if (iter != debugLocations.end()) {
+          auto location = iter->second;
+          debugLocations.erase(iter);
+          debugLocations[expression] = location;
+        }
+      }
+    }
     return *replacep = expression;
   }