[WebAssembly] Only mark non-hidden symbols as live if they are also defined

Previously we were also marking undefined symbols (i.e. imports)
as live.

Differential Revision: https://reviews.llvm.org/D48299

3 files changed, 23 insertions, 40 deletions

diff --git a/lld/test/wasm/gc-imports.ll b/lld/test/wasm/gc-imports.ll
index 066cd88daad..fbcb74dbdd3 100644
--- a/lld/test/wasm/gc-imports.ll
+++ b/lld/test/wasm/gc-imports.ll
@@ -1,15 +1,21 @@
 ; RUN: llc -filetype=obj %s -o %t.o
 ; RUN: yaml2obj %S/Inputs/undefined-globals.yaml -o %t_globals.o
-; RUN: wasm-ld -print-gc-sections --allow-undefined -o %t1.wasm %t.o %t_globals.o
+; RUN: wasm-ld --allow-undefined -o %t1.wasm %t.o %t_globals.o
 
 target triple = "wasm32-unknown-unknown"
 
-declare hidden i64 @unused_undef_function(i64 %arg)
+declare i64 @unused_undef_function(i64 %arg)
 
-declare hidden i32 @used_undef_function()
+declare i32 @used_undef_function()
 
 declare i64 @use_undef_global()
 
+define hidden void @foo() {
+entry:
+  call i64 @unused_undef_function(i64 0)
+  ret void
+}
+
 define hidden void @_start() {
 entry:
   call i32 @used_undef_function()
@@ -19,18 +25,7 @@ entry:
 
 ; RUN: obj2yaml %t1.wasm | FileCheck %s
 
-; CHECK:        - Type:            TYPE
-; CHECK-NEXT:     Signatures:
-; CHECK-NEXT:       - Index:           0
-; CHECK-NEXT:         ReturnType:      I32
-; CHECK-NEXT:         ParamTypes:
-; CHECK-NEXT:       - Index:           1
-; CHECK-NEXT:         ReturnType:      NORESULT
-; CHECK-NEXT:         ParamTypes:
-; CHECK-NEXT:       - Index:           2
-; CHECK-NEXT:         ReturnType:      I64
-; CHECK-NEXT:         ParamTypes:
-; CHECK-NEXT:   - Type:            IMPORT
+; CHECK:        - Type:            IMPORT
 ; CHECK-NEXT:     Imports:
 ; CHECK-NEXT:       - Module:          env
 ; CHECK-NEXT:         Field:           used_undef_function
@@ -55,33 +50,18 @@ entry:
 ; CHECK-NEXT:         Name:            use_undef_global
 ; CHECK-NEXT: ...
 
-; RUN: wasm-ld -print-gc-sections --no-gc-sections --allow-undefined \
+; RUN: wasm-ld --no-gc-sections --allow-undefined \
 ; RUN:     -o %t1.no-gc.wasm %t.o %t_globals.o
 ; RUN: obj2yaml %t1.no-gc.wasm | FileCheck %s -check-prefix=NO-GC
 
-; NO-GC:        - Type:            TYPE
-; NO-GC-NEXT:     Signatures:
-; NO-GC-NEXT:       - Index:           0
-; NO-GC-NEXT:         ReturnType:      I32
-; NO-GC-NEXT:         ParamTypes:
-; NO-GC-NEXT:       - Index:           1
-; NO-GC-NEXT:         ReturnType:      I64
-; NO-GC-NEXT:         ParamTypes:
-; NO-GC-NEXT:           - I64
-; NO-GC-NEXT:       - Index:           2
-; NO-GC-NEXT:         ReturnType:      NORESULT
-; NO-GC-NEXT:         ParamTypes:
-; NO-GC-NEXT:       - Index:           3
-; NO-GC-NEXT:         ReturnType:      I64
-; NO-GC-NEXT:         ParamTypes:
-; NO-GC-NEXT:   - Type:            IMPORT
+; NO-GC:        - Type:            IMPORT
 ; NO-GC-NEXT:     Imports:
 ; NO-GC-NEXT:       - Module:          env
-; NO-GC-NEXT:         Field:           used_undef_function
+; NO-GC-NEXT:         Field:           unused_undef_function
 ; NO-GC-NEXT:         Kind:            FUNCTION
 ; NO-GC-NEXT:         SigIndex:        0
 ; NO-GC-NEXT:       - Module:          env
-; NO-GC-NEXT:         Field:           unused_undef_function
+; NO-GC-NEXT:         Field:           used_undef_function
 ; NO-GC-NEXT:         Kind:            FUNCTION
 ; NO-GC-NEXT:         SigIndex:        1
 ; NO-GC-NEXT:       - Module:          env
@@ -99,13 +79,15 @@ entry:
 ; NO-GC-NEXT:     Name:            name
 ; NO-GC-NEXT:     FunctionNames:
 ; NO-GC-NEXT:       - Index:           0
-; NO-GC-NEXT:         Name:            used_undef_function
-; NO-GC-NEXT:       - Index:           1
 ; NO-GC-NEXT:         Name:            unused_undef_function
+; NO-GC-NEXT:       - Index:           1
+; NO-GC-NEXT:         Name:            used_undef_function
 ; NO-GC-NEXT:       - Index:           2
 ; NO-GC-NEXT:         Name:            __wasm_call_ctors
 ; NO-GC-NEXT:       - Index:           3
-; NO-GC-NEXT:         Name:            _start
+; NO-GC-NEXT:         Name:            foo
 ; NO-GC-NEXT:       - Index:           4
+; NO-GC-NEXT:         Name:            _start
+; NO-GC-NEXT:       - Index:           5
 ; NO-GC-NEXT:         Name:            use_undef_global
 ; NO-GC-NEXT: ...
diff --git a/lld/wasm/MarkLive.cpp b/lld/wasm/MarkLive.cpp
index 6b90690cca5..c9dbbf59c95 100644
--- a/lld/wasm/MarkLive.cpp
+++ b/lld/wasm/MarkLive.cpp
@@ -40,6 +40,7 @@ void lld::wasm::markLive() {
   auto Enqueue = [&](Symbol *Sym) {
     if (!Sym || Sym->isLive())
       return;
+    LLVM_DEBUG(dbgs() << "markLive: " << Sym->getName() << "\n");
     Sym->markLive();
     if (Sym->SignatureMismatch)
       error("function signature mismatch: " + Sym->getName());
@@ -52,9 +53,9 @@ void lld::wasm::markLive() {
     Enqueue(Symtab->find(Config->Entry));
   Enqueue(WasmSym::CallCtors);
 
-  // By default we export all non-hidden, so they are gc roots too
+  // We export all defined, non-hidden symbols so they are all gc roots too
   for (Symbol *Sym : Symtab->getSymbols())
-    if (!Sym->isHidden())
+    if (Sym->isDefined() && !Sym->isHidden())
       Enqueue(Sym);
 
   // The ctor functions are all used in the synthetic __wasm_call_ctors
diff --git a/lld/wasm/Symbols.h b/lld/wasm/Symbols.h
index 9b2d51e69f8..ab974770d36 100644
--- a/lld/wasm/Symbols.h
+++ b/lld/wasm/Symbols.h
@@ -105,7 +105,7 @@ protected:
   uint32_t Flags;
   InputFile *File;
   uint32_t OutputSymbolIndex = INVALID_INDEX;
-  bool Referenced = false;
+  bool Referenced;
 };
 
 class FunctionSymbol : public Symbol {