[SimplifyCFG] When eliminating `unreachable` landing pads, mark `call`s as `nounwind`

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, 5 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index d5d0232..569eee3 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -2557,11 +2557,14 @@ static bool markAliveBlocks(Function &F,
   return Changed;
 }
 
-void llvm::removeUnwindEdge(BasicBlock *BB, DomTreeUpdater *DTU) {
+void llvm::removeUnwindEdge(BasicBlock *BB, bool WouldUnwindBeUB,
+                            DomTreeUpdater *DTU) {
   Instruction *TI = BB->getTerminator();
 
   if (auto *II = dyn_cast<InvokeInst>(TI)) {
-    changeToCall(II, DTU);
+    CallInst *CI = changeToCall(II, DTU);
+    if (WouldUnwindBeUB && !CI->doesNotThrow())
+      CI->setDoesNotThrow();
     return;
   }