Add a --strip-dwarf pass (#2454)

This pass strips DWARF debug sections, but not other debug
sections. This is useful when emitting source maps, as we do
need the SourceMapURL section, but the DWARF sections are
not longer necessary (and we've seen a testcase where they
are massively large, so big the wasm can't even be loaded in
a browser...).

Also contains a trivial one-line fix in --extract-function which
was necessary to create the testcase here: that pass extracts
a function from a wasm file (like llvm-extract) but it didn't check
if an export already existed for the function.

6 files changed, 48 insertions, 6 deletions

diff --git a/src/passes/ExtractFunction.cpp b/src/passes/ExtractFunction.cpp
index 01daf3504..fbc1aa7c4 100644
--- a/src/passes/ExtractFunction.cpp
+++ b/src/passes/ExtractFunction.cpp
@@ -49,12 +49,14 @@ struct ExtractFunction : public Pass {
     module->memory.segments.clear();
     module->table.segments.clear();
     // leave just an export for the thing we want
-    module->exports.clear();
-    auto* export_ = new Export;
-    export_->name = name;
-    export_->value = name;
-    export_->kind = ExternalKind::Function;
-    module->addExport(export_);
+    if (!module->getExportOrNull(name)) {
+      module->exports.clear();
+      auto* export_ = new Export;
+      export_->name = name;
+      export_->value = name;
+      export_->kind = ExternalKind::Function;
+      module->addExport(export_);
+    }
   }
 };
 
diff --git a/src/passes/Strip.cpp b/src/passes/Strip.cpp
index e85379003..ace745f87 100644
--- a/src/passes/Strip.cpp
+++ b/src/passes/Strip.cpp
@@ -62,6 +62,12 @@ Pass* createStripDebugPass() {
   });
 }
 
+Pass* createStripDWARFPass() {
+  return new Strip([&](const UserSection& curr) {
+    return curr.name.find(".debug") == 0 || curr.name.find("reloc..debug") == 0;
+  });
+}
+
 Pass* createStripProducersPass() {
   return new Strip([&](const UserSection& curr) {
     return curr.name == BinaryConsts::UserSections::Producers;
diff --git a/src/passes/pass.cpp b/src/passes/pass.cpp
index 0f6507d98..9afea38e6 100644
--- a/src/passes/pass.cpp
+++ b/src/passes/pass.cpp
@@ -320,6 +320,7 @@ void PassRegistry::registerPasses() {
   registerPass("strip-debug",
                "strip debug info (including the names section)",
                createStripDebugPass);
+  registerPass("strip-dwarf", "strip dwarf debug info", createStripDWARFPass);
   registerPass("strip-producers",
                "strip the wasm producers section",
                createStripProducersPass);
diff --git a/src/passes/passes.h b/src/passes/passes.h
index caa02ac8a..cc33e4300 100644
--- a/src/passes/passes.h
+++ b/src/passes/passes.h
@@ -102,6 +102,7 @@ Pass* createSimplifyLocalsNoTeePass();
 Pass* createSimplifyLocalsNoStructurePass();
 Pass* createSimplifyLocalsNoTeeNoStructurePass();
 Pass* createStripDebugPass();
+Pass* createStripDWARFPass();
 Pass* createStripProducersPass();
 Pass* createStripTargetFeaturesPass();
 Pass* createSouperifyPass();
diff --git a/test/passes/strip-dwarf.bin.txt b/test/passes/strip-dwarf.bin.txt
new file mode 100644
index 000000000..2276090e7
--- /dev/null
+++ b/test/passes/strip-dwarf.bin.txt
@@ -0,0 +1,32 @@
+(module
+ (type $0 (func (result i32)))
+ (type $1 (func (param i32) (result i32)))
+ (type $2 (func))
+ (type $3 (func (param i32)))
+ (type $4 (func (param i32 i32)))
+ (import "env" "__wasm_call_ctors" (func $fimport$0))
+ (import "env" "dlmalloc" (func $fimport$1 (param i32) (result i32)))
+ (import "env" "dlfree" (func $fimport$2 (param i32)))
+ (import "env" "setThrew" (func $fimport$3 (param i32 i32)))
+ (import "env" "stackSave" (func $fimport$4 (result i32)))
+ (import "env" "stackAlloc" (func $fimport$5 (param i32) (result i32)))
+ (import "env" "stackRestore" (func $fimport$6 (param i32)))
+ (import "env" "__growWasmMemory" (func $fimport$7 (param i32) (result i32)))
+ (global $global$0 i32 (i32.const 1532))
+ (export "__wasm_call_ctors" (func $fimport$0))
+ (export "_Z3foov" (func $fimport$0))
+ (export "__errno_location" (func $0))
+ (export "setThrew" (func $fimport$3))
+ (export "malloc" (func $fimport$1))
+ (export "free" (func $fimport$2))
+ (export "__data_end" (global $global$0))
+ (export "stackSave" (func $fimport$4))
+ (export "stackAlloc" (func $fimport$5))
+ (export "stackRestore" (func $fimport$6))
+ (export "__growWasmMemory" (func $fimport$7))
+ (func $0 (; 8 ;) (type $0) (result i32)
+  (i32.const 1024)
+ )
+ ;; custom section "sourceMappingURL", size 15
+ ;; custom section "sourceMappingURL", size 15
+)
diff --git a/test/passes/strip-dwarf.wasm b/test/passes/strip-dwarf.wasm
new file mode 100644
index 000000000..b9c7378e8
--- /dev/null
+++ b/test/passes/strip-dwarf.wasm