[llvm-reduce] Do not crash when accessing landingpads of invokes.

[fhahn]

Summary

Unconditionally removing landing pads results in invalid IR,
if there is a different invoke that uses it. Update the code
to only remove the landing pad if the current invoke is the only
user. Also carefully avoid creating plain branches to bbs with
landing pads we couldn't remove.

[arsenm]

If it's temporarily invalid as in will fall the verifier, probably should try to avoid getting there in the first place

llvm/test/tools/llvm-reduce/invoke-with-missing-landingpad.ll

2

Should add -abort-on-invalid-reduction

[fhahn]

In D138072#3929124, @arsenm wrote:

If it's temporarily invalid as in will fall the verifier, probably should try to avoid getting there in the first place

Fair point! I updated the code to only remove the landing pad instruction if the current invoke is the only invoke using it. This also requires extra care when we cannot remove the landing pad and it would be the destination for the branch.

[fhahn]

llvm/test/tools/llvm-reduce/invoke-with-missing-landingpad.ll

2

Done, thanks!

[aeubanks]

llvm/test/tools/llvm-reduce/invoke-with-missing-landingpad.ll

2

looks like this wasn't done

[aeubanks]

otherwise lgtm

[fhahn]

llvm/test/tools/llvm-reduce/invoke-with-missing-landingpad.ll

2

Missed to include this in the recent update, fixed in the committed version.

llvm/test/tools/llvm-reduce/invoke-with-missing-landingpad.ll

+; RUN: llvm-reduce --delta-passes=basic-blocks --test FileCheck --test-arg --check-prefixes=CHECK-INTERESTINGNESS --test-arg %s --test-arg --input-file %s  -abort-on-invalid-reduction -o %t
+; RUN: FileCheck <%t %s
+
+; CHECK-INTERESTINGNESS: call void @foo()
+
+; CHECK: define void @test() personality ptr null {
+; CHECK-NEXT: entry:
+; CHECK-NEXT:   br label %cont
+; CHECK-EMPTY:
+; CHECK-NEXT: cont:
+; CHECK-NEXT:   br label %exit
+; CHECK-EMPTY:
+; CHECK-NEXT: exit:
+; CHECK-NEXT:   call void @foo()
+; CHECK-NEXT:   ret void
+; CHECK-NEXT: }
+
+define void @test() personality ptr null {
+entry:
+  invoke void @foo()
+          to label %cont unwind label %lpad
+
+cont:
+  invoke void @foo()
+          to label %exit unwind label %lpad
+
+lpad:
+  %0 = landingpad { ptr, i32 }
+          cleanup
+  ret void
+
+exit:
+  call void @foo()
+  ret void
+}
+
+declare void @foo()

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

static void replaceBranchTerminator(BasicBlock &BB,
 
   // BB only references Chunk BBs
   if (ChunkSuccessors.size() == Term->getNumSuccessors())
     return;
 
   bool IsBranch = isa<BranchInst>(Term);
   if (InvokeInst *Invoke = dyn_cast<InvokeInst>(Term)) {
     LandingPadInst *LP = Invoke->getLandingPadInst();
+    // Remove landingpad instruction if the containing block isn't used by other
+    // invokes.
+    if (none_of(LP->getParent()->users(), [Invoke](User *U) {
+          return U != Invoke && isa<InvokeInst>(U);
+        })) {
       LP->replaceAllUsesWith(getDefaultValue(LP->getType()));
       LP->eraseFromParent();
+    } else if (!ChunkSuccessors.empty() &&
+               ChunkSuccessors[0] == LP->getParent()) {
+      // If the selected successor is the landing pad, clear the chunk
+      // successors to avoid creating a regular branch to the landing pad which
+      // would result in invalid IR.
+      ChunkSuccessors.clear();
+    }
     IsBranch = true;
   }
 
   Value *Address = nullptr;
   if (auto *IndBI = dyn_cast<IndirectBrInst>(Term))
     Address = IndBI->getAddress();
 
   Term->replaceAllUsesWith(getDefaultValue(Term->getType()));