[Attributor][NFC] Do not delete dead blocks but "clear" them

Deleting blocks will require us to deal with dead edges, e.g.,
  `br i1 false, label %live, label %dead`
explicitly. For now we just clear the blocks and move on.
This will be revisited once we actually fold branches.

1 files changed, 6 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/IPO/Attributor.cpp b/llvm/lib/Transforms/IPO/Attributor.cpp
index 11a4939da78..129eb197674 100644
--- a/llvm/lib/Transforms/IPO/Attributor.cpp
+++ b/llvm/lib/Transforms/IPO/Attributor.cpp
@@ -4644,9 +4644,12 @@ ChangeStatus Attributor::run(Module &M) {
       SmallVector<BasicBlock *, 8> ToBeDeletedBBs;
       ToBeDeletedBBs.reserve(NumDeadBlocks);
       ToBeDeletedBBs.append(ToBeDeletedBlocks.begin(), ToBeDeletedBlocks.end());
-      DeleteDeadBlocks(ToBeDeletedBBs);
-      STATS_DECLTRACK(AAIsDead, BasicBlock,
-                      "Number of dead basic blocks deleted.");
+      // Actually we do not delete the blocks but squash them into a single
+      // unreachable but untangling branches that jump here is something we need
+      // to do in a more generic way.
+      DetatchDeadBlocks(ToBeDeletedBBs, nullptr);
+      STATS_DECL(AAIsDead, BasicBlock, "Number of dead basic blocks deleted.");
+      BUILD_STAT_NAME(AAIsDead, BasicBlock) += ToBeDeletedBlocks.size();
     }
 
     STATS_DECL(AAIsDead, Function, "Number of dead functions deleted.");