[llvm-reduce] Create returns with undef values for non-void functions.

[fhahn]

Summary

Currently replaceBranchTerminator/removeUninterestingBBsFromSwitch
always creates ret void instructions if no successor is in the chunk.

This results in invalid IR for functions with non-void return types,
which makes those reductions unfeasible. Instead, create ret ty undef
for functions with non-void return types.

[lebedev.ri]

llvm/test/Reduce/remove-bbs-ret-nonvoid.ll

6

Please use FileCheck, like most new tests do

[fhahn]

llvm/test/Reduce/remove-bbs-ret-nonvoid.ll

6

Guess I copied from the wrong test then :D

[fhahn]

Update test to use FileCheck for interestingness. Diff should now make the change clear, no switch required.

[lebedev.ri]

LG, thanks

llvm/test/Reduce/remove-bbs-ret-nonvoid.ll

 ; Test that llvm-reduce inserts valid return instructions for functions with
 ; on-void return types.
 ;
 ; RUN: llvm-reduce --test FileCheck --test-arg --check-prefixes=CHECK-INTERESTINGNESS --test-arg %s --test-arg --input-file %s -o %t
 ; RUN: cat %t | FileCheck %s
 
 ; CHECK-INTERESTINGNESS: interesting:
 ; CHECK-INTERESTINGNESS: interesting2:
 
 define i32 @main(i1 %c) {
 ; CHECK-LABEL: define i32 @main() {
 ; CHECK-LABEL: interesting:
 ; CHECK-NEXT:    br label %interesting2
 
 ; CHECK-LABEL: interesting2:
-; CHECK-NEXT:    br label %uninteresting1
-
-; CHECK-LABEL: uninteresting1:
-; CHECK-NEXT:    ret i32 10
+; CHECK-NEXT:    ret i32 undef
 
 interesting:
   br label %interesting2
 
 interesting2:
   br i1 true, label %uninteresting1, label %uninteresting
 
 uninteresting:
   br label %uninteresting1
 
 uninteresting1:
   ret i32 10
 }

llvm/tools/llvm-reduce/deltas/ReduceBasicBlocks.cpp

static void replaceBranchTerminator(BasicBlock &BB,
   Value *Address = nullptr;
   if (auto IndBI = dyn_cast<IndirectBrInst>(Term))
     Address = IndBI->getAddress();
 
   Term->replaceAllUsesWith(UndefValue::get(Term->getType()));
   Term->eraseFromParent();
 
   if (ChunkSucessors.empty()) {
-    ReturnInst::Create(BB.getContext(), nullptr, &BB);
+    auto *FnRetTy = BB.getParent()->getReturnType();
+    ReturnInst::Create(BB.getContext(),
+                       FnRetTy->isVoidTy() ? nullptr : UndefValue::get(FnRetTy),
+                       &BB);
     return;
   }
 
   if (IsBranch)
     BranchInst::Create(ChunkSucessors[0], &BB);
 
   if (Address) {
     auto NewIndBI =
         IndirectBrInst::Create(Address, ChunkSucessors.size(), &BB);
     for (auto Dest : ChunkSucessors)
       NewIndBI->addDestination(Dest);
   }
 }
 
 /// Removes uninteresting BBs from switch, if the default case ends up being
 /// uninteresting, the switch is replaced with a void return (since it has to be
 /// replace with something)
 static void removeUninterestingBBsFromSwitch(SwitchInst &SwInst,
                                              std::set<BasicBlock *> BBsToKeep) {
   if (!BBsToKeep.count(SwInst.getDefaultDest())) {
-    ReturnInst::Create(SwInst.getContext(), nullptr, SwInst.getParent());
+    auto *FnRetTy = SwInst.getParent()->getParent()->getReturnType();
+    ReturnInst::Create(SwInst.getContext(),
+                       FnRetTy->isVoidTy() ? nullptr : UndefValue::get(FnRetTy),
+                       SwInst.getParent());
     SwInst.eraseFromParent();
   } else
     for (int I = 0, E = SwInst.getNumCases(); I != E; ++I) {
       auto Case = SwInst.case_begin() + I;
       if (!BBsToKeep.count(Case->getCaseSuccessor())) {
         SwInst.removeCase(Case);
         --I;
         --E;