[SimplifyCFG] Reapply: when eliminating `unreachable` landing pads, mark `call`s as `nounwind`

This time the change is in it's least intrusive form since only the return
type in prototype for `removeUnwindEdge()` is changed, since only a single
specific caller need that knowledge.

We really can't recover that knowledge, and `nounwind` knowledge,
(and not just a lack of the unwind edge, aka `call` instead of `invoke`),
is e.g. part of the reasoning in e.g. `mayHaveSideEffects()`.

Note that this is call-site-specific knowledge,
just because some callsite had an `unreachable`
unwind edge, does not mean that all will.

1 files changed, 4 insertions, 5 deletions

diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index d5d0232..a8a7b64 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -2557,13 +2557,11 @@ static bool markAliveBlocks(Function &F,
   return Changed;
 }
 
-void llvm::removeUnwindEdge(BasicBlock *BB, DomTreeUpdater *DTU) {
+Instruction *llvm::removeUnwindEdge(BasicBlock *BB, DomTreeUpdater *DTU) {
   Instruction *TI = BB->getTerminator();
 
-  if (auto *II = dyn_cast<InvokeInst>(TI)) {
-    changeToCall(II, DTU);
-    return;
-  }
+  if (auto *II = dyn_cast<InvokeInst>(TI))
+    return changeToCall(II, DTU);
 
   Instruction *NewTI;
   BasicBlock *UnwindDest;
@@ -2591,6 +2589,7 @@ void llvm::removeUnwindEdge(BasicBlock *BB, DomTreeUpdater *DTU) {
   TI->eraseFromParent();
   if (DTU)
     DTU->applyUpdates({{DominatorTree::Delete, BB, UnwindDest}});
+  return NewTI;
 }
 
 /// removeUnreachableBlocks - Remove blocks that are not reachable, even