[llvm-commits] [llvm] r86264 - in /llvm/trunk: lib/Transforms/Scalar/JumpThreading.cpp test/Transforms/JumpThreading/basic.ll
Chris Lattner
sabre at nondot.org
Fri Nov 6 10:15:15 PST 2009
Author: lattner
Date: Fri Nov 6 12:15:14 2009
New Revision: 86264
URL: http://llvm.org/viewvc/llvm-project?rev=86264&view=rev
Log:
Extend jump threading to support much more general threading
predicates. This allows us to jump thread things like:
_ZN12StringSwitchI5ColorE4CaseILj7EEERS1_RAT__KcRKS0_.exit119:
%tmp1.i24166 = phi i8 [ 1, %bb5.i117 ], [ %tmp1.i24165, %_Z....exit ], [ %tmp1.i24165, %bb4.i114 ]
%toBoolnot.i87 = icmp eq i8 %tmp1.i24166, 0 ; <i1> [#uses=1]
%tmp4.i90 = icmp eq i32 %tmp2.i, 6 ; <i1> [#uses=1]
%or.cond173 = and i1 %toBoolnot.i87, %tmp4.i90 ; <i1> [#uses=1]
br i1 %or.cond173, label %bb4.i96, label %_ZN12...
Where it is "obvious" that when coming from %bb5.i117 that the 'and' is always
false. This triggers a surprisingly high number of times in the testsuite,
and gets us closer to generating good code for doug's strswitch testcase.
This also make a bunch of other code in jump threading redundant, I'll rip
out in the next patch. This survived an enable-checking llvm-gcc bootstrap.
Modified:
llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp
llvm/trunk/test/Transforms/JumpThreading/basic.ll
Modified: llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp?rev=86264&r1=86263&r2=86264&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp Fri Nov 6 12:15:14 2009
@@ -75,8 +75,16 @@
bool ThreadEdge(BasicBlock *BB, BasicBlock *PredBB, BasicBlock *SuccBB);
bool DuplicateCondBranchOnPHIIntoPred(BasicBlock *BB,
BasicBlock *PredBB);
-
BasicBlock *FactorCommonPHIPreds(PHINode *PN, Value *Val);
+
+ typedef SmallVectorImpl<std::pair<ConstantInt*,
+ BasicBlock*> > PredValueInfo;
+
+ bool ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB,
+ PredValueInfo &Result);
+ bool ProcessThreadableEdges(Instruction *CondInst, BasicBlock *BB);
+
+
bool ProcessBranchOnDuplicateCond(BasicBlock *PredBB, BasicBlock *DestBB);
bool ProcessSwitchOnDuplicateCond(BasicBlock *PredBB, BasicBlock *DestBB);
@@ -220,7 +228,133 @@
&CommonPreds[0], CommonPreds.size(),
".thr_comm", this);
}
+
+/// GetResultOfComparison - Given an icmp/fcmp predicate and the left and right
+/// hand sides of the compare instruction, try to determine the result. If the
+/// result can not be determined, a null pointer is returned.
+static Constant *GetResultOfComparison(CmpInst::Predicate pred,
+ Value *LHS, Value *RHS) {
+ if (Constant *CLHS = dyn_cast<Constant>(LHS))
+ if (Constant *CRHS = dyn_cast<Constant>(RHS))
+ return ConstantExpr::getCompare(pred, CLHS, CRHS);
+
+ if (LHS == RHS)
+ if (isa<IntegerType>(LHS->getType()) || isa<PointerType>(LHS->getType()))
+ if (ICmpInst::isTrueWhenEqual(pred))
+ return ConstantInt::getTrue(LHS->getContext());
+ else
+ return ConstantInt::getFalse(LHS->getContext());
+ return 0;
+}
+
+
+/// ComputeValueKnownInPredecessors - Given a basic block BB and a value V, see
+/// if we can infer that the value is a known ConstantInt in any of our
+/// predecessors. If so, return the known the list of value and pred BB in the
+/// result vector. If a value is known to be undef, it is returned as null.
+///
+/// The BB basic block is known to start with a PHI node.
+///
+/// This returns true if there were any known values.
+///
+///
+/// TODO: Per PR2563, we could infer value range information about a predecessor
+/// based on its terminator.
+bool JumpThreading::
+ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB,PredValueInfo &Result){
+ PHINode *TheFirstPHI = cast<PHINode>(BB->begin());
+
+ // If V is a constantint, then it is known in all predecessors.
+ if (isa<ConstantInt>(V) || isa<UndefValue>(V)) {
+ ConstantInt *CI = dyn_cast<ConstantInt>(V);
+ Result.resize(TheFirstPHI->getNumIncomingValues());
+ for (unsigned i = 0, e = Result.size(); i != e; ++i)
+ Result.push_back(std::make_pair(CI, TheFirstPHI->getIncomingBlock(i)));
+ return true;
+ }
+ // If V is a non-instruction value, or an instruction in a different block,
+ // then it can't be derived from a PHI.
+ Instruction *I = dyn_cast<Instruction>(V);
+ if (I == 0 || I->getParent() != BB)
+ return false;
+
+ /// If I is a PHI node, then we know the incoming values for any constants.
+ if (PHINode *PN = dyn_cast<PHINode>(I)) {
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
+ Value *InVal = PN->getIncomingValue(i);
+ if (isa<ConstantInt>(InVal) || isa<UndefValue>(InVal)) {
+ ConstantInt *CI = dyn_cast<ConstantInt>(InVal);
+ Result.push_back(std::make_pair(CI, PN->getIncomingBlock(i)));
+ }
+ }
+ return !Result.empty();
+ }
+
+ SmallVector<std::pair<ConstantInt*, BasicBlock*>, 8> LHSVals, RHSVals;
+
+ // Handle some boolean conditions.
+ if (I->getType()->getPrimitiveSizeInBits() == 1) {
+ // X | true -> true
+ // X & false -> false
+ if (I->getOpcode() == Instruction::Or ||
+ I->getOpcode() == Instruction::And) {
+ ComputeValueKnownInPredecessors(I->getOperand(0), BB, LHSVals);
+ ComputeValueKnownInPredecessors(I->getOperand(1), BB, RHSVals);
+
+ if (LHSVals.empty() && RHSVals.empty())
+ return false;
+
+ ConstantInt *InterestingVal;
+ if (I->getOpcode() == Instruction::Or)
+ InterestingVal = ConstantInt::getTrue(I->getContext());
+ else
+ InterestingVal = ConstantInt::getFalse(I->getContext());
+
+ // Scan for the sentinel.
+ for (unsigned i = 0, e = LHSVals.size(); i != e; ++i)
+ if (LHSVals[i].first == InterestingVal || LHSVals[i].first == 0)
+ Result.push_back(LHSVals[i]);
+ for (unsigned i = 0, e = RHSVals.size(); i != e; ++i)
+ if (RHSVals[i].first == InterestingVal || RHSVals[i].first == 0)
+ Result.push_back(RHSVals[i]);
+ return !Result.empty();
+ }
+
+ // TODO: Should handle the NOT form of XOR.
+
+ }
+
+ // Handle compare with phi operand, where the PHI is defined in this block.
+ if (CmpInst *Cmp = dyn_cast<CmpInst>(I)) {
+ PHINode *PN = dyn_cast<PHINode>(Cmp->getOperand(0));
+ if (PN && PN->getParent() == BB) {
+ // We can do this simplification if any comparisons fold to true or false.
+ // See if any do.
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
+ BasicBlock *PredBB = PN->getIncomingBlock(i);
+ Value *LHS = PN->getIncomingValue(i);
+ Value *RHS = Cmp->getOperand(1)->DoPHITranslation(BB, PredBB);
+
+ Constant *Res = GetResultOfComparison(Cmp->getPredicate(), LHS, RHS);
+ if (Res == 0) continue;
+
+ if (isa<UndefValue>(Res))
+ Result.push_back(std::make_pair((ConstantInt*)0, PredBB));
+ else if (ConstantInt *CI = dyn_cast<ConstantInt>(Res))
+ Result.push_back(std::make_pair(CI, PredBB));
+ }
+
+ return !Result.empty();
+ }
+
+ // TODO: We could also recurse to see if we can determine constants another
+ // way.
+ }
+ return false;
+}
+
+
/// GetBestDestForBranchOnUndef - If we determine that the specified block ends
/// in an undefined jump, decide which block is best to revector to.
@@ -251,7 +385,7 @@
// successor, merge the blocks. This encourages recursive jump threading
// because now the condition in this block can be threaded through
// predecessors of our predecessor block.
- if (BasicBlock *SinglePred = BB->getSinglePredecessor())
+ if (BasicBlock *SinglePred = BB->getSinglePredecessor()) {
if (SinglePred->getTerminator()->getNumSuccessors() == 1 &&
SinglePred != BB) {
// If SinglePred was a loop header, BB becomes one.
@@ -267,10 +401,10 @@
BB->moveBefore(&BB->getParent()->getEntryBlock());
return true;
}
-
- // See if this block ends with a branch or switch. If so, see if the
- // condition is a phi node. If so, and if an entry of the phi node is a
- // constant, we can thread the block.
+ }
+
+ // Look to see if the terminator is a branch of switch, if not we can't thread
+ // it.
Value *Condition;
if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
// Can't thread an unconditional jump.
@@ -369,7 +503,7 @@
}
// If we have a comparison, loop over the predecessors to see if there is
- // a condition with the same value.
+ // a condition with a lexically identical value.
pred_iterator PI = pred_begin(BB), E = pred_end(BB);
for (; PI != E; ++PI)
if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
@@ -402,6 +536,19 @@
if (SimplifyPartiallyRedundantLoad(LI))
return true;
+
+ // Handle a variety of cases where we are branching on something derived from
+ // a PHI node in the current block. If we can prove that any predecessors
+ // compute a predictable value based on a PHI node, thread those predecessors.
+ //
+ // We only bother doing this if the current block has a PHI node and if the
+ // conditional instruction lives in the current block. If either condition
+ // fail, this won't be a computable value anyway.
+ if (CondInst->getParent() == BB && isa<PHINode>(BB->front()))
+ if (ProcessThreadableEdges(CondInst, BB))
+ return true;
+
+
// TODO: If we have: "br (X > 0)" and we have a predecessor where we know
// "(X == 4)" thread through this block.
@@ -690,6 +837,176 @@
return true;
}
+/// FindMostPopularDest - The specified list contains multiple possible
+/// threadable destinations. Pick the one that occurs the most frequently in
+/// the list.
+static BasicBlock *
+FindMostPopularDest(BasicBlock *BB,
+ const SmallVectorImpl<std::pair<BasicBlock*,
+ BasicBlock*> > &PredToDestList) {
+ assert(!PredToDestList.empty());
+
+ // Determine popularity. If there are multiple possible destinations, we
+ // explicitly choose to ignore 'undef' destinations. We prefer to thread
+ // blocks with known and real destinations to threading undef. We'll handle
+ // them later if interesting.
+ DenseMap<BasicBlock*, unsigned> DestPopularity;
+ for (unsigned i = 0, e = PredToDestList.size(); i != e; ++i)
+ if (PredToDestList[i].second)
+ DestPopularity[PredToDestList[i].second]++;
+
+ // Find the most popular dest.
+ DenseMap<BasicBlock*, unsigned>::iterator DPI = DestPopularity.begin();
+ BasicBlock *MostPopularDest = DPI->first;
+ unsigned Popularity = DPI->second;
+ SmallVector<BasicBlock*, 4> SamePopularity;
+
+ for (++DPI; DPI != DestPopularity.end(); ++DPI) {
+ // If the popularity of this entry isn't higher than the popularity we've
+ // seen so far, ignore it.
+ if (DPI->second < Popularity)
+ ; // ignore.
+ else if (DPI->second == Popularity) {
+ // If it is the same as what we've seen so far, keep track of it.
+ SamePopularity.push_back(DPI->first);
+ } else {
+ // If it is more popular, remember it.
+ SamePopularity.clear();
+ MostPopularDest = DPI->first;
+ Popularity = DPI->second;
+ }
+ }
+
+ // Okay, now we know the most popular destination. If there is more than
+ // destination, we need to determine one. This is arbitrary, but we need
+ // to make a deterministic decision. Pick the first one that appears in the
+ // successor list.
+ if (!SamePopularity.empty()) {
+ SamePopularity.push_back(MostPopularDest);
+ TerminatorInst *TI = BB->getTerminator();
+ for (unsigned i = 0; ; ++i) {
+ assert(i != TI->getNumSuccessors() && "Didn't find any successor!");
+
+ if (std::find(SamePopularity.begin(), SamePopularity.end(),
+ TI->getSuccessor(i)) == SamePopularity.end())
+ continue;
+
+ MostPopularDest = TI->getSuccessor(i);
+ break;
+ }
+ }
+
+ // Okay, we have finally picked the most popular destination.
+ return MostPopularDest;
+}
+
+bool JumpThreading::ProcessThreadableEdges(Instruction *CondInst,
+ BasicBlock *BB) {
+ // If threading this would thread across a loop header, don't even try to
+ // thread the edge.
+ if (LoopHeaders.count(BB))
+ return false;
+
+
+
+ SmallVector<std::pair<ConstantInt*, BasicBlock*>, 8> PredValues;
+ if (!ComputeValueKnownInPredecessors(CondInst, BB, PredValues))
+ return false;
+ assert(!PredValues.empty() &&
+ "ComputeValueKnownInPredecessors returned true with no values");
+
+ DEBUG(errs() << "IN BB: " << *BB;
+ for (unsigned i = 0, e = PredValues.size(); i != e; ++i) {
+ errs() << " BB '" << BB->getName() << "': FOUND condition = ";
+ if (PredValues[i].first)
+ errs() << *PredValues[i].first;
+ else
+ errs() << "UNDEF";
+ errs() << " for pred '" << PredValues[i].second->getName()
+ << "'.\n";
+ });
+
+ // Decide what we want to thread through. Convert our list of known values to
+ // a list of known destinations for each pred. This also discards duplicate
+ // predecessors and keeps track of the undefined inputs (which are represented
+ // as a null dest in the PredToDestList.
+ SmallPtrSet<BasicBlock*, 16> SeenPreds;
+ SmallVector<std::pair<BasicBlock*, BasicBlock*>, 16> PredToDestList;
+
+ BasicBlock *OnlyDest = 0;
+ BasicBlock *MultipleDestSentinel = (BasicBlock*)(intptr_t)~0ULL;
+
+ for (unsigned i = 0, e = PredValues.size(); i != e; ++i) {
+ BasicBlock *Pred = PredValues[i].second;
+ if (!SeenPreds.insert(Pred))
+ continue; // Duplicate predecessor entry.
+
+ // If the predecessor ends with an indirect goto, we can't change its
+ // destination.
+ if (isa<IndirectBrInst>(Pred->getTerminator()))
+ continue;
+
+ ConstantInt *Val = PredValues[i].first;
+
+ BasicBlock *DestBB;
+ if (Val == 0) // Undef.
+ DestBB = 0;
+ else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator()))
+ DestBB = BI->getSuccessor(Val->isZero());
+ else {
+ SwitchInst *SI = cast<SwitchInst>(BB->getTerminator());
+ DestBB = SI->getSuccessor(SI->findCaseValue(Val));
+ }
+
+ // If we have exactly one destination, remember it for efficiency below.
+ if (i == 0)
+ OnlyDest = DestBB;
+ else if (OnlyDest != DestBB)
+ OnlyDest = MultipleDestSentinel;
+
+ PredToDestList.push_back(std::make_pair(Pred, DestBB));
+ }
+
+ // If all edges were unthreadable, we fail.
+ if (PredToDestList.empty())
+ return false;
+
+ // Determine which is the most common successor. If we have many inputs and
+ // this block is a switch, we want to start by threading the batch that goes
+ // to the most popular destination first. If we only know about one
+ // threadable destination (the common case) we can avoid this.
+ BasicBlock *MostPopularDest = OnlyDest;
+
+ if (MostPopularDest == MultipleDestSentinel)
+ MostPopularDest = FindMostPopularDest(BB, PredToDestList);
+
+ // Now that we know what the most popular destination is, factor all
+ // predecessors that will jump to it into a single predecessor.
+ SmallVector<BasicBlock*, 16> PredsToFactor;
+ for (unsigned i = 0, e = PredToDestList.size(); i != e; ++i)
+ if (PredToDestList[i].second == MostPopularDest)
+ PredsToFactor.push_back(PredToDestList[i].first);
+
+ BasicBlock *PredToThread;
+ if (PredsToFactor.size() == 1)
+ PredToThread = PredsToFactor[0];
+ else {
+ DEBUG(errs() << " Factoring out " << PredsToFactor.size()
+ << " common predecessors.\n");
+ PredToThread = SplitBlockPredecessors(BB, &PredsToFactor[0],
+ PredsToFactor.size(),
+ ".thr_comm", this);
+ }
+
+ // If the threadable edges are branching on an undefined value, we get to pick
+ // the destination that these predecessors should get to.
+ if (MostPopularDest == 0)
+ MostPopularDest = BB->getTerminator()->
+ getSuccessor(GetBestDestForJumpOnUndef(BB));
+
+ // Ok, try to thread it!
+ return ThreadEdge(BB, PredToThread, MostPopularDest);
+}
/// ProcessJumpOnPHI - We have a conditional branch or switch on a PHI node in
/// the current block. See if there are any simplifications we can do based on
@@ -814,24 +1131,6 @@
return ThreadEdge(BB, PredBB, SuccBB);
}
-/// GetResultOfComparison - Given an icmp/fcmp predicate and the left and right
-/// hand sides of the compare instruction, try to determine the result. If the
-/// result can not be determined, a null pointer is returned.
-static Constant *GetResultOfComparison(CmpInst::Predicate pred,
- Value *LHS, Value *RHS,
- LLVMContext &Context) {
- if (Constant *CLHS = dyn_cast<Constant>(LHS))
- if (Constant *CRHS = dyn_cast<Constant>(RHS))
- return ConstantExpr::getCompare(pred, CLHS, CRHS);
-
- if (LHS == RHS)
- if (isa<IntegerType>(LHS->getType()) || isa<PointerType>(LHS->getType()))
- return ICmpInst::isTrueWhenEqual(pred) ?
- ConstantInt::getTrue(Context) : ConstantInt::getFalse(Context);
-
- return 0;
-}
-
/// ProcessBranchOnCompare - We found a branch on a comparison between a phi
/// node and a value. If we can identify when the comparison is true between
/// the phi inputs and the value, we can fold the compare for that edge and
@@ -852,8 +1151,7 @@
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
PredVal = PN->getIncomingValue(i);
- Constant *Res = GetResultOfComparison(Cmp->getPredicate(), PredVal,
- RHS, Cmp->getContext());
+ Constant *Res = GetResultOfComparison(Cmp->getPredicate(), PredVal, RHS);
if (!Res) {
PredVal = 0;
continue;
Modified: llvm/trunk/test/Transforms/JumpThreading/basic.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/JumpThreading/basic.ll?rev=86264&r1=86263&r2=86264&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/JumpThreading/basic.ll (original)
+++ llvm/trunk/test/Transforms/JumpThreading/basic.ll Fri Nov 6 12:15:14 2009
@@ -170,5 +170,36 @@
}
+;; This tests that the branch in 'merge' can be cloned up into T1.
+;; rdar://7367025
+define i32 @test7(i1 %cond, i1 %cond2) {
+Entry:
+; CHECK: @test7
+ %v1 = call i32 @f1()
+ br i1 %cond, label %Merge, label %F1
+F1:
+ %v2 = call i32 @f2()
+ br label %Merge
+
+Merge:
+ %B = phi i32 [%v1, %Entry], [%v2, %F1]
+ %M = icmp ne i32 %B, %v1
+ %N = icmp eq i32 %B, 47
+ %O = and i1 %M, %N
+ br i1 %O, label %T2, label %F2
+
+; CHECK: Merge:
+; CHECK-NOT: phi
+; CHECK-NEXT: %v2 = call i32 @f2()
+
+T2:
+ call void @f3()
+ ret i32 %B
+
+F2:
+ ret i32 %B
+; CHECK: F2:
+; CHECK-NEXT: phi i32
+}
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