[PATCH] D50721: [WebAssembly] Preserve function signatures during LTO

[Sam Clegg via Phabricator via llvm-commits]

sbc100 created this revision.
Herald added subscribers: llvm-commits, dexonsmith, steven_wu, sunfish, aheejin, jgravelle-google, inglorion, mehdi_amini, dschuff.

With LTO when and undefined function (with a known signature)
in replaced by a defined bitcode function we were loosing the
signature information (since bitcode functions don't have
signatures).

With this change we preserve the original signature from the
undefined function and verify that the post LTO compiled
function has the correct signature.

This change improves the error handling in the case where
there is a signature mismatch with a function defined in
a bitcode file.


Repository:
  rLLD LLVM Linker

https://reviews.llvm.org/D50721

Files:
  wasm/LTO.cpp
  wasm/SymbolTable.cpp


Index: wasm/SymbolTable.cpp
===================================================================
--- wasm/SymbolTable.cpp
+++ wasm/SymbolTable.cpp
@@ -201,7 +201,9 @@
 Symbol *SymbolTable::addDefinedFunction(StringRef Name, uint32_t Flags,
                                         InputFile *File,
                                         InputFunction *Function) {
-  LLVM_DEBUG(dbgs() << "addDefinedFunction: " << Name << "\n");
+  LLVM_DEBUG(dbgs() << "addDefinedFunction: " << Name << " ["
+                    << (Function ? toString(Function->Signature) : "none")
+                    << "]\n");
   Symbol *S;
   bool WasInserted;
   std::tie(S, WasInserted) = insert(Name, File);
@@ -214,8 +216,12 @@
   if (Function)
     checkFunctionType(S, File, &Function->Signature);
 
-  if (shouldReplace(S, File, Flags))
-    replaceSymbol<DefinedFunction>(S, Name, Flags, File, Function);
+  if (shouldReplace(S, File, Flags)) {
+    const WasmSignature *OldSig = cast<FunctionSymbol>(S)->FunctionType;
+    auto NewSym = replaceSymbol<DefinedFunction>(S, Name, Flags, File, Function);
+    if (!NewSym->FunctionType)
+      NewSym->FunctionType = OldSig;
+  }
   return S;
 }
 
@@ -263,7 +269,8 @@
 Symbol *SymbolTable::addUndefinedFunction(StringRef Name, uint32_t Flags,
                                           InputFile *File,
                                           const WasmSignature *Sig) {
-  LLVM_DEBUG(dbgs() << "addUndefinedFunction: " << Name << "\n");
+  LLVM_DEBUG(dbgs() << "addUndefinedFunction: " << Name <<
+             " [" << (Sig ? toString(*Sig) : "none") << "]\n");
 
   Symbol *S;
   bool WasInserted;
Index: wasm/LTO.cpp
===================================================================
--- wasm/LTO.cpp
+++ wasm/LTO.cpp
@@ -72,10 +72,11 @@
 BitcodeCompiler::~BitcodeCompiler() = default;
 
 static void undefine(Symbol *S) {
-  if (isa<DefinedFunction>(S))
-    replaceSymbol<UndefinedFunction>(S, S->getName(), 0);
+  if (auto F = dyn_cast<DefinedFunction>(S))
+    replaceSymbol<UndefinedFunction>(F, F->getName(), 0, F->getFile(),
+                                     F->FunctionType);
   else if (isa<DefinedData>(S))
-    replaceSymbol<UndefinedData>(S, S->getName(), 0);
+    replaceSymbol<UndefinedData>(S, S->getName(), 0, S->getFile());
   else
     llvm_unreachable("unexpected symbol kind");
 }


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