llvm-extract: Replace IFuncs with declarations

[Dinistro]

Summary

This commit ensures that llvm-extract does not copy all IFuncs into the
resulting modules. Before this change, ifuncs were not modified which
could cause the emission unexpected IR files.

[Dinistro]

@darthscsi I added you as a reviewer, as you were the original author of this pass. There was no other substantial contributions to this pass in a long time. If you know of someone else to assign, feel free to do so.

[darthscsi]

LGTM.

llvm/lib/Transforms/IPO/ExtractGV.cpp

static void makeVisible(GlobalValue &GV, bool Delete) {
   }
 
   if (!GV.hasLinkOnceLinkage()) {
     assert(!GV.isDiscardableIfUnused());
     return;
   }
 
   // Map linkonce* to weak* so that llvm doesn't drop this GV.
-  switch(GV.getLinkage()) {
+  switch (GV.getLinkage()) {
   default:
     llvm_unreachable("Unexpected linkage");
   case GlobalValue::LinkOnceAnyLinkage:
     GV.setLinkage(GlobalValue::WeakAnyLinkage);
     return;
   case GlobalValue::LinkOnceODRLinkage:
     GV.setLinkage(GlobalValue::WeakODRLinkage);
     return;
   }
 }
 
-
-    /// If deleteS is true, this pass deletes the specified global values.
-    /// Otherwise, it deletes as much of the module as possible, except for the
-    /// global values specified.
 ExtractGVPass::ExtractGVPass(std::vector<GlobalValue *> &GVs, bool deleteS,
                              bool keepConstInit)
     : Named(GVs.begin(), GVs.end()), deleteStuff(deleteS),
       keepConstInit(keepConstInit) {}
 
 PreservedAnalyses ExtractGVPass::run(Module &M, ModuleAnalysisManager &) {
   // Visit the global inline asm.
   if (!deleteStuff)
if (Delete) {
         Declaration = new GlobalVariable(
             M, Ty, false, GlobalValue::ExternalLinkage, nullptr, GA.getName());
       }
       GA.replaceAllUsesWith(Declaration);
       delete &GA;
     }
   }
 
+  // Visit the IFuncs.
+  for (GlobalIFunc &IF : llvm::make_early_inc_range(M.ifuncs())) {
+    bool Delete = deleteStuff == (bool)Named.count(&IF);
+    makeVisible(IF, Delete);
+
+    if (!Delete)
+      continue;
+
+    auto *FuncType = dyn_cast<FunctionType>(IF.getValueType());
+    IF.removeFromParent();
+    llvm::Value *Declaration =
+        Function::Create(FuncType, GlobalValue::ExternalLinkage,
+                         IF.getAddressSpace(), IF.getName(), &M);
+    IF.replaceAllUsesWith(Declaration);
+    delete &IF;
+  }
+
   return PreservedAnalyses::none();
 }

llvm/test/tools/llvm-extract/delete-ifunc.ll

+; RUN: llvm-extract -func foo -S %s | FileCheck %s
+
+; llvm-extract should not copy ifuncs into the new module, so make sure they
+; are turned into declarations.
+
+; CHECK: define void @foo() {
+; CHECK: call void @ifunc()
+define void @foo() {
+  call void @ifunc()
+  ret void
+}
+
+define void @ifunc_impl() {
+  ret void
+}
+
+; CHECK: declare void @ifunc()
+@ifunc = ifunc void (), ptr @ifunc_resolver
+
+define internal ptr @ifunc_resolver() {
+  ret ptr @ifunc_impl
+}