[wasm-split] Do not split out the start function

src/ir/module-splitting.cpp

@@ -353,10 +353,10 @@ struct ModuleSplitter {
     classifyFunctions();
     moveSecondaryFunctions();
     thunkExportedSecondaryFunctions();
-    shareImportableItems();
     indirectReferencesToSecondaryFunctions();
     indirectCallsToSecondaryFunctions();
     exportImportCalledPrimaryFunctions();
+    shareImportableItems();
     setupTablePatching();
   }
 };
@@ -432,11 +432,11 @@ void ModuleSplitter::classifyFunctions() {
     configSecondaryFuncs.insert(funcs.begin(), funcs.end());
   }
   for (auto& func : primary.functions) {
+    // The start function must always be kept in the primary module.
     if (func->imported() || !configSecondaryFuncs.contains(func->name) ||
-        segmentReferrers.contains(func->name)) {
+        segmentReferrers.contains(func->name) || func->name == primary.start) {
       primaryFuncs.insert(func->name);
     } else {
-      assert(func->name != primary.start && "The start function must be kept");
       allSecondaryFuncs.insert(func->name);
     }
   }

src/tools/wasm-split/wasm-split.cpp

@@ -296,6 +296,13 @@ void splitModule(const WasmSplitOptions& options) {
       }
       continue;
     }
+    if (function->name == wasm.start) {
+      if (!options.quiet) {
+        std::cerr << "warning: cannot split out start function " << func
+                  << "\n";
+      }
+      continue;
+    }
     if (!options.quiet && options.keepFuncs.contains(func)) {
       std::cerr << "warning: function " << func
                 << " was to be both kept and split. It will be split.\n";

test/lit/wasm-split/active-table-base-global-used-elsewhere.wast

@@ -40,7 +40,7 @@
  (func $keep
   (call $split)
  )
- ;; SECONDARY:      (import "primary" "table" (table $table 1 funcref))
+ ;; SECONDARY:      (import "primary" "table" (table $table 2 funcref))
 
  ;; SECONDARY:      (import "primary" "global" (global $base i32))
 

test/lit/wasm-split/multi-split-start.wast

@@ -0,0 +1,86 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py --all-items and should not be edited.
+
+;; RUN: wasm-split -all -g --multi-split %s --manifest %s.manifest --out-prefix=%t -o %t.wasm
+;; RUN: wasm-dis %t.wasm | filecheck %s --check-prefix=PRIMARY
+;; RUN: wasm-dis %t1.wasm | filecheck %s --check-prefix=MOD1
+;; RUN: wasm-dis %t2.wasm | filecheck %s --check-prefix=MOD2
+;; RUN: wasm-dis %t3.wasm | filecheck %s --check-prefix=MOD3
+
+;; The start function, $C, cannot be split it, and will remain in the primary.
+
+(module
+ ;; PRIMARY:      (type $0 (func))
+
+ ;; PRIMARY:      (import "placeholder.2" "0" (func $placeholder_0))
+
+ ;; PRIMARY:      (table $0 1 funcref)
+
+ ;; PRIMARY:      (elem $0 (i32.const 0) $placeholder_0)
+
+ ;; PRIMARY:      (export "C" (func $C))
+
+ ;; PRIMARY:      (export "table" (table $0))
+
+ ;; PRIMARY:      (start $C)
+ (start $C)
+
+ ;; MOD1:      (type $0 (func))
+
+ ;; MOD1:      (import "primary" "table" (table $timport$0 1 funcref))
+
+ ;; MOD1:      (import "primary" "C" (func $C (exact)))
+
+ ;; MOD1:      (func $A
+ ;; MOD1-NEXT:  (call $A)
+ ;; MOD1-NEXT:  (call_indirect (type $0)
+ ;; MOD1-NEXT:   (i32.const 0)
+ ;; MOD1-NEXT:  )
+ ;; MOD1-NEXT:  (call $C)
+ ;; MOD1-NEXT: )
+ (func $A
+  (call $A)
+  (call $B)
+  (call $C)
+ )
+
+ ;; MOD2:      (type $0 (func))
+
+ ;; MOD2:      (import "primary" "table" (table $timport$0 1 funcref))
+
+ ;; MOD2:      (elem $0 (i32.const 0) $B)
+
+ ;; MOD2:      (func $B
+ ;; MOD2-NEXT:  (drop
+ ;; MOD2-NEXT:   (i32.const 42)
+ ;; MOD2-NEXT:  )
+ ;; MOD2-NEXT: )
+ (func $B
+  (drop
+   (i32.const 42)
+  )
+ )
+
+ ;; PRIMARY:      (func $C
+ ;; PRIMARY-NEXT:  (drop
+ ;; PRIMARY-NEXT:   (i32.const 1337)
+ ;; PRIMARY-NEXT:  )
+ ;; PRIMARY-NEXT: )
+ (func $C
+  (drop
+   (i32.const 1337)
+  )
+ )
+
+ ;; MOD3:      (type $0 (func))
+
+ ;; MOD3:      (func $D
+ ;; MOD3-NEXT:  (drop
+ ;; MOD3-NEXT:   (i32.const 999999)
+ ;; MOD3-NEXT:  )
+ ;; MOD3-NEXT: )
+ (func $D
+  (drop
+   (i32.const 999999)
+  )
+ )
+)

test/lit/wasm-split/multi-split-start.wast.manifest

@@ -0,0 +1,9 @@
+1:
+A
+
+2:
+B
+
+3:
+C
+D

test/lit/wasm-split/split-module-items.wast

@@ -34,11 +34,11 @@
  ;; PRIMARY:      (tag $keep-tag (type $1) (param i32))
  ;; PRIMARY-NEXT: (tag $shared-tag (type $1) (param i32))
 
- ;; PRIMARY:      (export "memory" (memory $shared-memory))
+ ;; PRIMARY:      (export "keep" (func $keep))
+ ;; PRIMARY-NEXT: (export "memory" (memory $shared-memory))
  ;; PRIMARY-NEXT: (export "table" (table $shared-table))
  ;; PRIMARY-NEXT: (export "global" (global $shared-global))
  ;; PRIMARY-NEXT: (export "tag" (tag $shared-tag))
- ;; PRIMARY-NEXT: (export "keep" (func $keep))
  ;; PRIMARY-NEXT: (export "table_5" (table $2))
 
  ;; SECONDARY:      (import "primary" "memory" (memory $shared-memory 1 1))

test/lit/wasm-split/start.wast

@@ -0,0 +1,28 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py --all-items and should not be edited.
+
+;; RUN: wasm-split %s --split-funcs=start_func,other -o1 %t.1.wasm -o2 %t.2.wasm -g 2>&1
+;; RUN: wasm-dis -all %t.1.wasm | filecheck %s --check-prefix PRIMARY
+;; RUN: wasm-dis -all %t.2.wasm | filecheck %s --check-prefix SECONDARY
+
+;; Do not error on trying to split out the start function. It cannot be
+;; split out, keep it in the primary module.
+
+(module
+  ;; PRIMARY:      (type $0 (func))
+
+  ;; PRIMARY:      (start $start_func)
+
+  ;; PRIMARY:      (func $start_func (type $0)
+  ;; PRIMARY-NEXT: )
+  (func $start_func)
+
+  (start $start_func)
+
+  ;; SECONDARY:      (type $0 (func))
+
+  ;; SECONDARY:      (func $other (type $0)
+  ;; SECONDARY-NEXT: )
+  (func $other)
+)
+
+