Default mainReadsParams to true in standalone mode (#2906)

The process of DCE'ing the argument handling is already handled in
a different way in standalone more.   In standalone mode the entry
point is `_start` which takes no args, and argv code is included
on-demand via the presence or absence the wasi syscalls for argument
processing (__wasi_args_get/__wasi_args_sizes_get).

6 files changed, 21 insertions, 20 deletions

diff --git a/src/wasm/wasm-emscripten.cpp b/src/wasm/wasm-emscripten.cpp
index c2cace488..a57573254 100644
--- a/src/wasm/wasm-emscripten.cpp
+++ b/src/wasm/wasm-emscripten.cpp
@@ -1224,25 +1224,31 @@ std::string EmscriptenGlueGenerator::generateEmscriptenMetadata(
   });
   meta << "\n  ],\n";
 
-  auto mainReadsParams = false;
-  auto* exp = wasm.getExportOrNull("main");
-  if (!exp) {
-    exp = wasm.getExportOrNull("__main_argc_argv");
-  }
-  if (exp) {
-    if (exp->kind == ExternalKind::Function) {
-      auto* main = wasm.getFunction(exp->value);
-      mainReadsParams = true;
-      // If main does not read its parameters, it will just be a stub that
-      // calls __original_main (which has no parameters).
-      if (auto* call = main->body->dynCast<Call>()) {
-        if (call->operands.empty()) {
-          mainReadsParams = false;
+  // In normal mode we attempt to determine if main takes argumnts or not
+  // In standalone mode we export _start instead and rely on the presence
+  // of the __wasi_args_get and __wasi_args_sizes_get syscalls allow us to
+  // DCE to the argument handling JS code instead.
+  if (!standalone) {
+    auto mainReadsParams = false;
+    auto* exp = wasm.getExportOrNull("main");
+    if (!exp) {
+      exp = wasm.getExportOrNull("__main_argc_argv");
+    }
+    if (exp) {
+      if (exp->kind == ExternalKind::Function) {
+        auto* main = wasm.getFunction(exp->value);
+        mainReadsParams = true;
+        // If main does not read its parameters, it will just be a stub that
+        // calls __original_main (which has no parameters).
+        if (auto* call = main->body->dynCast<Call>()) {
+          if (call->operands.empty()) {
+            mainReadsParams = false;
+          }
         }
       }
     }
+    meta << "  \"mainReadsParams\": " << int(mainReadsParams) << '\n';
   }
-  meta << "  \"mainReadsParams\": " << int(mainReadsParams) << '\n';
 
   meta << "}\n";
 
diff --git a/test/lld/safe_stack_standalone-wasm.wat.out b/test/lld/safe_stack_standalone-wasm.wat.out
index e39b076ff..81f62a0dd 100644
--- a/test/lld/safe_stack_standalone-wasm.wat.out
+++ b/test/lld/safe_stack_standalone-wasm.wat.out
@@ -187,7 +187,6 @@
   ],
   "features": [
   ],
-  "mainReadsParams": 0
 }
 -- END METADATA --
 ;)
diff --git a/test/lld/standalone-wasm-with-start.wat.out b/test/lld/standalone-wasm-with-start.wat.out
index 4e2d8cbc4..367a26168 100644
--- a/test/lld/standalone-wasm-with-start.wat.out
+++ b/test/lld/standalone-wasm-with-start.wat.out
@@ -45,7 +45,6 @@
   ],
   "features": [
   ],
-  "mainReadsParams": 0
 }
 -- END METADATA --
 ;)
diff --git a/test/lld/standalone-wasm.wat.out b/test/lld/standalone-wasm.wat.out
index 179878979..3a483bdf7 100644
--- a/test/lld/standalone-wasm.wat.out
+++ b/test/lld/standalone-wasm.wat.out
@@ -60,7 +60,6 @@
   ],
   "features": [
   ],
-  "mainReadsParams": 0
 }
 -- END METADATA --
 ;)
diff --git a/test/lld/standalone-wasm2.wat.out b/test/lld/standalone-wasm2.wat.out
index 5d2198d8d..d6a0c5505 100644
--- a/test/lld/standalone-wasm2.wat.out
+++ b/test/lld/standalone-wasm2.wat.out
@@ -57,7 +57,6 @@
   ],
   "features": [
   ],
-  "mainReadsParams": 1
 }
 -- END METADATA --
 ;)
diff --git a/test/lld/standalone-wasm3.wat.out b/test/lld/standalone-wasm3.wat.out
index 3634ca46e..65557a790 100644
--- a/test/lld/standalone-wasm3.wat.out
+++ b/test/lld/standalone-wasm3.wat.out
@@ -38,7 +38,6 @@
   ],
   "features": [
   ],
-  "mainReadsParams": 0
 }
 -- END METADATA --
 ;)