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Add support to ADCE for pruning unreachable blocks. This addresses the final

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part of PR2509.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@53038 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Owen Anderson
2008-07-02 18:05:19 +00:00
parent 6ed2d1ecdb
commit 77d76b7ef7
2 changed files with 80 additions and 1 deletions
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44
lib/Transforms/Scalar/ADCE.cpp
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@@ -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 @@ namespace {
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 @@ static RegisterPass<ADCE> X("adce", "Aggressive Dead Code Elimination");
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)