[lld] r352575 - [WebAssembly] Fix undefined weak function symbols in LTO builds

[Sam Clegg via llvm-commits]

Author: sbc
Date: Tue Jan 29 16:25:52 2019
New Revision: 352575

URL: http://llvm.org/viewvc/llvm-project?rev=352575&view=rev
Log:
[WebAssembly] Fix undefined weak function symbols in LTO builds

Summary: Fixes PR40219

Subscribers: dschuff, mehdi_amini, inglorion, jgravelle-google, aheejin, sunfish, steven_wu, dexonsmith, llvm-commits

Differential Revision: https://reviews.llvm.org/D57420

Added:
    lld/trunk/test/wasm/lto/weak-undefined.ll
Modified:
    lld/trunk/wasm/Driver.cpp

Added: lld/trunk/test/wasm/lto/weak-undefined.ll
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/wasm/lto/weak-undefined.ll?rev=352575&view=auto
==============================================================================
--- lld/trunk/test/wasm/lto/weak-undefined.ll (added)
+++ lld/trunk/test/wasm/lto/weak-undefined.ll Tue Jan 29 16:25:52 2019
@@ -0,0 +1,20 @@
+; RUN: llvm-as %s -o %t.o
+; RUN: wasm-ld %t.o -o %t.wasm
+; RUN: obj2yaml %t.wasm | FileCheck %s
+
+; Test that undefined weak external functions are handled in the LTO case
+; We had a bug where stub function generation was failing because functions
+; that are in bitcode (pre-LTO) don't have signatures assigned.
+
+target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
+target triple = "wasm32-unknown-unknown"
+
+declare extern_weak i32 @foo()
+
+define void @_start() #0 {
+entry:
+    %call2 = call i32 @foo()
+    ret void
+}
+
+; CHECK: Name:            undefined function foo

Modified: lld/trunk/wasm/Driver.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/wasm/Driver.cpp?rev=352575&r1=352574&r2=352575&view=diff
==============================================================================
--- lld/trunk/wasm/Driver.cpp (original)
+++ lld/trunk/wasm/Driver.cpp Tue Jan 29 16:25:52 2019
@@ -587,9 +587,6 @@ void LinkerDriver::link(ArrayRef<const c
 
   Symbol *EntrySym = nullptr;
   if (!Config->Relocatable) {
-    // Add synthetic dummies for weak undefined functions.
-    handleWeakUndefines();
-
     if (!Config->Shared && !Config->Entry.empty()) {
       EntrySym = handleUndefined(Config->Entry);
       if (EntrySym && EntrySym->isDefined())
@@ -613,6 +610,11 @@ void LinkerDriver::link(ArrayRef<const c
   if (errorCount())
     return;
 
+  // Add synthetic dummies for weak undefined functions.  Must happen
+  // after LTO otherwise functions may not yet have signatures.
+  if (!Config->Relocatable)
+    handleWeakUndefines();
+
   if (EntrySym)
     EntrySym->setHidden(false);