//
// This file implements the Aggressive Dead Code Elimination pass. This pass
// optimistically assumes that all instructions are dead until proven otherwise,
-// allowing it to eliminate dead computations that other DCE passes do not
+// allowing it to eliminate dead computations that other DCE passes do not
// catch, particularly involving loop computations.
//
//===----------------------------------------------------------------------===//
-#define DEBUG_TYPE "adce"
#include "llvm/Transforms/Scalar.h"
-#include "llvm/BasicBlock.h"
-#include "llvm/Instructions.h"
-#include "llvm/IntrinsicInst.h"
-#include "llvm/Pass.h"
-#include "llvm/Support/CFG.h"
-#include "llvm/Support/InstIterator.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/CFG.h"
+#include "llvm/IR/InstIterator.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/Pass.h"
using namespace llvm;
+#define DEBUG_TYPE "adce"
+
STATISTIC(NumRemoved, "Number of instructions removed");
namespace {
- struct ADCE : public FunctionPass {
- static char ID; // Pass identification, replacement for typeid
- ADCE() : FunctionPass(ID) {
- initializeADCEPass(*PassRegistry::getPassRegistry());
- }
-
- virtual bool runOnFunction(Function& F);
-
- virtual void getAnalysisUsage(AnalysisUsage& AU) const {
- AU.setPreservesCFG();
- }
-
- };
+struct ADCE : public FunctionPass {
+ static char ID; // Pass identification, replacement for typeid
+ ADCE() : FunctionPass(ID) {
+ initializeADCEPass(*PassRegistry::getPassRegistry());
+ }
+
+ bool runOnFunction(Function& F) override;
+
+ void getAnalysisUsage(AnalysisUsage& AU) const override {
+ AU.setPreservesCFG();
+ }
+};
}
char ADCE::ID = 0;
INITIALIZE_PASS(ADCE, "adce", "Aggressive Dead Code Elimination", false, false)
bool ADCE::runOnFunction(Function& F) {
- SmallPtrSet<Instruction*, 128> alive;
- SmallVector<Instruction*, 128> worklist;
-
+ if (skipOptnoneFunction(F))
+ return false;
+
+ SmallPtrSet<Instruction*, 128> Alive;
+ SmallVector<Instruction*, 128> Worklist;
+
// Collect the set of "root" instructions that are known live.
- for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
- if (isa<TerminatorInst>(I.getInstructionIterator()) ||
- isa<DbgInfoIntrinsic>(I.getInstructionIterator()) ||
- I->mayHaveSideEffects()) {
- alive.insert(I.getInstructionIterator());
- worklist.push_back(I.getInstructionIterator());
+ for (Instruction &I : inst_range(F)) {
+ if (isa<TerminatorInst>(I) || isa<DbgInfoIntrinsic>(I) ||
+ isa<LandingPadInst>(I) || I.mayHaveSideEffects()) {
+ Alive.insert(&I);
+ Worklist.push_back(&I);
}
-
+ }
+
// Propagate liveness backwards to operands.
- while (!worklist.empty()) {
- Instruction* curr = worklist.pop_back_val();
-
- for (Instruction::op_iterator OI = curr->op_begin(), OE = curr->op_end();
- OI != OE; ++OI)
- if (Instruction* Inst = dyn_cast<Instruction>(OI))
- if (alive.insert(Inst))
- worklist.push_back(Inst);
+ while (!Worklist.empty()) {
+ Instruction *Curr = Worklist.pop_back_val();
+ for (Use &OI : Curr->operands()) {
+ if (Instruction *Inst = dyn_cast<Instruction>(OI))
+ if (Alive.insert(Inst).second)
+ Worklist.push_back(Inst);
+ }
}
-
+
// The inverse of the live set is the dead set. These are those instructions
// which have no side effects and do not influence the control flow or return
// value of the function, and may therefore be deleted safely.
- // NOTE: We reuse the worklist vector here for memory efficiency.
- for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
- if (!alive.count(I.getInstructionIterator())) {
- worklist.push_back(I.getInstructionIterator());
- I->dropAllReferences();
+ // NOTE: We reuse the Worklist vector here for memory efficiency.
+ for (Instruction &I : inst_range(F)) {
+ if (!Alive.count(&I)) {
+ Worklist.push_back(&I);
+ I.dropAllReferences();
}
-
- for (SmallVector<Instruction*, 1024>::iterator I = worklist.begin(),
- E = worklist.end(); I != E; ++I) {
+ }
+
+ for (Instruction *&I : Worklist) {
++NumRemoved;
- (*I)->eraseFromParent();
+ I->eraseFromParent();
}
- return !worklist.empty();
+ return !Worklist.empty();
}
FunctionPass *llvm::createAggressiveDCEPass() {