Add support to ADCE for pruning unreachable blocks. This addresses the final
part of PR2509.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@53038 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/ADCE.cpp b/lib/Transforms/Scalar/ADCE.cpp
index b9b828d..f7035e5 100644
--- a/lib/Transforms/Scalar/ADCE.cpp
+++ b/lib/Transforms/Scalar/ADCE.cpp
@@ -16,12 +16,15 @@
#define DEBUG_TYPE "adce"
#include "llvm/Transforms/Scalar.h"
+#include "llvm/BasicBlock.h"
#include "llvm/Instructions.h"
#include "llvm/Pass.h"
+#include "llvm/Support/CFG.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/InstIterator.h"
-#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/DenseSet.h"
+#include "llvm/ADT/DepthFirstIterator.h"
+#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/SmallVector.h"
using namespace llvm;
@@ -36,6 +39,9 @@
DenseSet<Instruction*> alive;
SmallVector<Instruction*, 1024> worklist;
+ DenseSet<BasicBlock*> reachable;
+ SmallVector<BasicBlock*, 1024> unreachable;
+
virtual bool runOnFunction(Function& F);
virtual void getAnalysisUsage(AnalysisUsage& AU) const {
@@ -51,6 +57,42 @@
bool ADCE::runOnFunction(Function& F) {
alive.clear();
worklist.clear();
+ reachable.clear();
+ unreachable.clear();
+
+ // First, collect the set of reachable blocks ...
+ for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
+ DE = df_end(&F.getEntryBlock()); DI != DE; ++DI)
+ reachable.insert(*DI);
+
+ // ... and then invert it into the list of unreachable ones. These
+ // blocks will be removed from the function.
+ for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
+ if (!reachable.count(FI))
+ unreachable.push_back(FI);
+
+ // Prepare to remove blocks by removing the PHI node entries for those blocks
+ // in their successors, and remove them from reference counting.
+ for (SmallVector<BasicBlock*, 1024>::iterator UI = unreachable.begin(),
+ UE = unreachable.end(); UI != UE; ++UI) {
+ BasicBlock* BB = *UI;
+ for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
+ SI != SE; ++SI) {
+ BasicBlock* succ = *SI;
+ BasicBlock::iterator succ_inst = succ->begin();
+ while (PHINode* P = dyn_cast<PHINode>(succ_inst)) {
+ P->removeIncomingValue(BB);
+ ++succ_inst;
+ }
+ }
+
+ BB->dropAllReferences();
+ }
+
+ // Finally, erase the unreachable blocks.
+ for (SmallVector<BasicBlock*, 1024>::iterator UI = unreachable.begin(),
+ UE = unreachable.end(); UI != UE; ++UI)
+ (*UI)->eraseFromParent();
// Collect the set of "root" instructions that are known live.
for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)