[llvm-commits] [PATCH] [msan] Remove unreachable bb's

[Evgeniy Stepanov]

  I've moved the code to BasicBlockUtils, in case we want to reuse it.

Hi kcc, chandlerc,

http://llvm-reviews.chandlerc.com/D208

CHANGE SINCE LAST DIFF
  http://llvm-reviews.chandlerc.com/D208?vs=504&id=523#toc

Files:
  include/llvm/Transforms/Utils/BasicBlockUtils.h
  lib/Transforms/Instrumentation/MemorySanitizer.cpp
  lib/Transforms/Scalar/SimplifyCFGPass.cpp
  lib/Transforms/Utils/BasicBlockUtils.cpp

Index: include/llvm/Transforms/Utils/BasicBlockUtils.h
===================================================================
--- include/llvm/Transforms/Utils/BasicBlockUtils.h
+++ include/llvm/Transforms/Utils/BasicBlockUtils.h
@@ -228,6 +228,10 @@
 TerminatorInst *SplitBlockAndInsertIfThen(Instruction *Cmp,
     bool Unreachable, MDNode *BranchWeights = 0);
 
+/// RemoveUnreachableBlocks - Remove all blocks that can not be reached from the
+/// function's entry.
+void RemoveUnreachableBlocks(Function &F);
+
 } // End llvm namespace
 
 #endif
Index: lib/Transforms/Instrumentation/MemorySanitizer.cpp
===================================================================
--- lib/Transforms/Instrumentation/MemorySanitizer.cpp
+++ lib/Transforms/Instrumentation/MemorySanitizer.cpp
@@ -477,6 +477,9 @@
   bool runOnFunction() {
     MS.initializeCallbacks(*F.getParent());
     if (!MS.TD) return false;
+
+    RemoveUnreachableBlocks(F);
+
     // Iterate all BBs in depth-first order and create shadow instructions
     // for all instructions (where applicable).
     // For PHI nodes we create dummy shadow PHIs which will be finalized later.
Index: lib/Transforms/Scalar/SimplifyCFGPass.cpp
===================================================================
--- lib/Transforms/Scalar/SimplifyCFGPass.cpp
+++ lib/Transforms/Scalar/SimplifyCFGPass.cpp
@@ -111,13 +111,11 @@
 
   SmallVector<BasicBlock*, 128> Worklist;
   Worklist.push_back(BB);
+  Reachable.insert(BB);
   bool Changed = false;
   do {
     BB = Worklist.pop_back_val();
 
-    if (!Reachable.insert(BB))
-      continue;
-
     // Do a quick scan of the basic block, turning any obviously unreachable
     // instructions into LLVM unreachable insts.  The instruction combining pass
     // canonicalizes unreachable insts into stores to null or undef.
@@ -176,7 +174,8 @@
 
     Changed |= ConstantFoldTerminator(BB, true);
     for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
-      Worklist.push_back(*SI);
+      if (Reachable.insert(*SI))
+        Worklist.push_back(*SI);
   } while (!Worklist.empty());
   return Changed;
 }
Index: lib/Transforms/Utils/BasicBlockUtils.cpp
===================================================================
--- lib/Transforms/Utils/BasicBlockUtils.cpp
+++ lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -726,3 +726,30 @@
   ReplaceInstWithInst(HeadOldTerm, HeadNewTerm);
   return CheckTerm;
 }
+
+/// RemoveUnreachableBlocks - Remove all blocks that can not be reached from the
+/// function's entry.
+void llvm::RemoveUnreachableBlocks(Function &F) {
+  SmallPtrSet<BasicBlock*, 128> Reachable;
+  SmallVector<BasicBlock*, 128> Worklist;
+  Worklist.push_back(&F.getEntryBlock());
+  Reachable.insert(&F.getEntryBlock());
+  do {
+    BasicBlock *BB = Worklist.pop_back_val();
+    for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
+      if (Reachable.insert(*SI))
+        Worklist.push_back(*SI);
+  } while (!Worklist.empty());
+
+  if (Reachable.size() == F.size())
+    return;
+
+  assert(Reachable.size() < F.size());
+  for (Function::iterator BB = ++F.begin(); BB != F.end();)
+    if (!Reachable.count(BB)) {
+      if (!BB->use_empty())
+        BB->replaceAllUsesWith(UndefValue::get(BB->getType()));
+      DeleteDeadBlock(BB++);
+    } else
+      ++BB;
+}
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