[Utils] Extract EliminateUnreachableBlocks (NFC)

Summary:
Extract the functionality of eliminating unreachable basic blocks
within a function, previously encapsulated within the
-unreachableblockelim pass, and make it available as a function within
BlockUtils.h. No functional change intended other than making the logic
reusable.

Exposing this logic makes it easier to implement
https://reviews.llvm.org/D59068, which fixes coroutines bug
https://bugs.llvm.org/show_bug.cgi?id=40979.

Reviewers: mkazantsev, wmi, davidxl, silvas, davide

Reviewed By: davide

Subscribers: llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D59069

llvm-svn: 355846

1 files changed, 2 insertions, 23 deletions

diff --git a/llvm/lib/CodeGen/UnreachableBlockElim.cpp b/llvm/lib/CodeGen/UnreachableBlockElim.cpp
index 57e548c703a..177bab32bcc 100644
--- a/llvm/lib/CodeGen/UnreachableBlockElim.cpp
+++ b/llvm/lib/CodeGen/UnreachableBlockElim.cpp
@@ -40,31 +40,10 @@
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
 using namespace llvm;
 
-static bool eliminateUnreachableBlock(Function &F) {
-  df_iterator_default_set<BasicBlock*> Reachable;
-
-  // Mark all reachable blocks.
-  for (BasicBlock *BB : depth_first_ext(&F, Reachable))
-    (void)BB/* Mark all reachable blocks */;
-
-  // Collect all dead blocks.
-  std::vector<BasicBlock*> DeadBlocks;
-  for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
-    if (!Reachable.count(&*I)) {
-      BasicBlock *BB = &*I;
-      DeadBlocks.push_back(BB);
-    }
-
-  // Delete the dead blocks.
-  DeleteDeadBlocks(DeadBlocks);
-
-  return !DeadBlocks.empty();
-}
-
 namespace {
 class UnreachableBlockElimLegacyPass : public FunctionPass {
   bool runOnFunction(Function &F) override {
-    return eliminateUnreachableBlock(F);
+    return llvm::EliminateUnreachableBlocks(F);
   }
 
 public:
@@ -89,7 +68,7 @@ FunctionPass *llvm::createUnreachableBlockEliminationPass() {
 
 PreservedAnalyses UnreachableBlockElimPass::run(Function &F,
                                                 FunctionAnalysisManager &AM) {
-  bool Changed = eliminateUnreachableBlock(F);
+  bool Changed = llvm::EliminateUnreachableBlocks(F);
   if (!Changed)
     return PreservedAnalyses::all();
   PreservedAnalyses PA;