[PATCH] D58488: [WebAssembly] Default to something reasonable in WebAssemblyAddMissingPrototypes

[Sam Clegg via Phabricator via llvm-commits]

sbc100 created this revision.
Herald added subscribers: llvm-commits, sunfish, aheejin, hiraditya, jgravelle-google, dschuff.
Herald added a project: LLVM.

Previously if we couldn't derive a prototype for a "no-prototype"
function from C we would leave it as is:

  void foo(...)

With this change we instead give is an empty signature and remove
the "no-prototype" attribute.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D58488

Files:
  llvm/lib/Target/WebAssembly/WebAssemblyAddMissingPrototypes.cpp
  llvm/test/CodeGen/WebAssembly/add-prototypes.ll


Index: llvm/test/CodeGen/WebAssembly/add-prototypes.ll
===================================================================
--- llvm/test/CodeGen/WebAssembly/add-prototypes.ll
+++ llvm/test/CodeGen/WebAssembly/add-prototypes.ll
@@ -58,6 +58,9 @@
 
 declare void @func_param(i64 (...)*)
 
+; CHECK: declare void @func_not_called()
+declare void @func_not_called(...) #1
+
 ; CHECK: declare extern_weak i64 @foo(i32)
 declare extern_weak i64 @foo(...) #1
 
Index: llvm/lib/Target/WebAssembly/WebAssemblyAddMissingPrototypes.cpp
===================================================================
--- llvm/lib/Target/WebAssembly/WebAssemblyAddMissingPrototypes.cpp
+++ llvm/lib/Target/WebAssembly/WebAssemblyAddMissingPrototypes.cpp
@@ -86,7 +86,6 @@
     // Create a function prototype based on the first call site (first bitcast)
     // that we find.
     FunctionType *NewType = nullptr;
-    Function *NewF = nullptr;
     for (Use &U : F.uses()) {
       LLVM_DEBUG(dbgs() << "prototype-less use: " << F.getName() << "\n");
       LLVM_DEBUG(dbgs() << *U.getUser() << "\n");
@@ -97,10 +96,6 @@
             // Create a new function with the correct type
             NewType = DestType;
             LLVM_DEBUG(dbgs() << "found function type: " << *NewType << "\n");
-            NewF = Function::Create(NewType, F.getLinkage(), F.getName() + ".fixed_sig");
-            NewF->setAttributes(F.getAttributes());
-            NewF->removeFnAttr("no-prototype");
-            Replacements.emplace_back(&F, NewF);
           } else if (NewType != DestType) {
             errs() << "warning: prototype-less function used with "
                       "conflicting signatures: "
@@ -116,8 +111,19 @@
       LLVM_DEBUG(
           dbgs() << "could not derive a function prototype from usage: " +
                         F.getName() + "\n");
-      continue;
+      // We could not derive a type for this function.  In this case strip
+      // the isVarArg and make it a simple zero-arg function.  This has more
+      // chance of being correct.  The current signature of (...) is illegal in
+      // C since it doesn't have any arguments before the "...", we this at
+      // least makes it possible for this symbol to be resolved by the linker.
+      NewType = FunctionType::get(F.getFunctionType()->getReturnType(), false);
     }
+
+    Function *NewF =
+        Function::Create(NewType, F.getLinkage(), F.getName() + ".fixed_sig");
+    NewF->setAttributes(F.getAttributes());
+    NewF->removeFnAttr("no-prototype");
+    Replacements.emplace_back(&F, NewF);
   }
 
   for (auto &Pair : Replacements) {
@@ -126,7 +132,7 @@
     std::string Name = OldF->getName();
     M.getFunctionList().push_back(NewF);
     OldF->replaceAllUsesWith(
-      ConstantExpr::getPointerBitCastOrAddrSpaceCast(NewF, OldF->getType()));
+        ConstantExpr::getPointerBitCastOrAddrSpaceCast(NewF, OldF->getType()));
     OldF->eraseFromParent();
     NewF->setName(Name);
   }


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