Previously, RecursivelyDeleteDeadInstructions provided an option
of returning a list of pointers to Values that are deleted. This was
unsafe, because the pointers in the list are, by nature of what
RecursivelyDeleteDeadInstructions does, always dangling. Replace this
with a simple callback mechanism. This may eventually be removed if
all clients can reasonably be expected to use CallbackVH.
Use this to factor out the dead-phi-cycle-elimination code from LSR
utility function, and generalize it to use the
RecursivelyDeleteTriviallyDeadInstructions utility function.
This makes LSR more aggressive about eliminating dead PHI cycles;
adjust tests to either be less trivial or to simply expect fewer
instructions.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@70636 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index e550200..b940665 100644
--- a/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -32,6 +32,7 @@
#include "llvm/Support/Debug.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/ValueHandle.h"
#include "llvm/Target/TargetLowering.h"
#include <algorithm>
using namespace llvm;
@@ -2138,6 +2139,7 @@
CondUse = &IVUsesByStride[*NewStride].Users.back();
CondStride = NewStride;
++NumEliminated;
+ Changed = true;
}
return Cond;
@@ -2501,44 +2503,21 @@
StrideOrder.clear();
// Clean up after ourselves
- if (!DeadInsts.empty()) {
+ if (!DeadInsts.empty())
DeleteTriviallyDeadInstructions();
- BasicBlock::iterator I = L->getHeader()->begin();
- while (PHINode *PN = dyn_cast<PHINode>(I++)) {
- // At this point, we know that we have killed one or more IV users.
- // It is worth checking to see if the cannonical indvar is also
- // dead, so that we can remove it as well.
- //
- // We can remove a PHI if it is on a cycle in the def-use graph
- // where each node in the cycle has degree one, i.e. only one use,
- // and is an instruction with no side effects.
- //
- // FIXME: this needs to eliminate an induction variable even if it's being
- // compared against some value to decide loop termination.
- if (!PN->hasOneUse())
- continue;
-
- SmallPtrSet<PHINode *, 4> PHIs;
- for (Instruction *J = dyn_cast<Instruction>(*PN->use_begin());
- J && J->hasOneUse() && !J->mayWriteToMemory();
- J = dyn_cast<Instruction>(*J->use_begin())) {
- // If we find the original PHI, we've discovered a cycle.
- if (J == PN) {
- // Break the cycle and mark the PHI for deletion.
- SE->deleteValueFromRecords(PN);
- PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
- DeadInsts.push_back(PN);
- Changed = true;
- break;
- }
- // If we find a PHI more than once, we're on a cycle that
- // won't prove fruitful.
- if (isa<PHINode>(J) && !PHIs.insert(cast<PHINode>(J)))
- break;
- }
+ // At this point, it is worth checking to see if any recurrence PHIs are also
+ // dead, so that we can remove them as well. To keep ScalarEvolution
+ // current, use a ValueDeletionListener class.
+ struct LSRListener : public ValueDeletionListener {
+ ScalarEvolution &SE;
+ explicit LSRListener(ScalarEvolution &se) : SE(se) {}
+
+ virtual void ValueWillBeDeleted(Value *V) {
+ SE.deleteValueFromRecords(V);
}
- DeleteTriviallyDeadInstructions();
- }
+ } VDL(*SE);
+ DeleteDeadPHIs(L->getHeader(), &VDL);
+
return Changed;
}
diff --git a/lib/Transforms/Utils/BasicBlockUtils.cpp b/lib/Transforms/Utils/BasicBlockUtils.cpp
index 97460bf..076f89e 100644
--- a/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -22,6 +22,8 @@
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Target/TargetData.h"
+#include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Support/ValueHandle.h"
#include <algorithm>
using namespace llvm;
@@ -73,6 +75,24 @@
}
+/// DeleteDeadPHIs - Examine each PHI in the given block and delete it if it
+/// is dead. Also recursively delete any operands that become dead as
+/// a result. This includes tracing the def-use list from the PHI to see if
+/// it is ultimately unused or if it reaches an unused cycle. If a
+/// ValueDeletionListener is specified, it is notified of the deletions.
+void llvm::DeleteDeadPHIs(BasicBlock *BB, ValueDeletionListener *VDL) {
+ // Recursively deleting a PHI may cause multiple PHIs to be deleted
+ // or RAUW'd undef, so use an array of WeakVH for the PHIs to delete.
+ SmallVector<WeakVH, 8> PHIs;
+ for (BasicBlock::iterator I = BB->begin();
+ PHINode *PN = dyn_cast<PHINode>(I); ++I)
+ PHIs.push_back(PN);
+
+ for (unsigned i = 0, e = PHIs.size(); i != e; ++i)
+ if (PHINode *PN = dyn_cast_or_null<PHINode>(PHIs[i].operator Value*()))
+ RecursivelyDeleteDeadPHINode(PN, VDL);
+}
+
/// MergeBlockIntoPredecessor - Attempts to merge a block into its predecessor,
/// if possible. The return value indicates success or failure.
bool llvm::MergeBlockIntoPredecessor(BasicBlock* BB, Pass* P) {
diff --git a/lib/Transforms/Utils/Local.cpp b/lib/Transforms/Utils/Local.cpp
index 4be1b87..3b36362 100644
--- a/lib/Transforms/Utils/Local.cpp
+++ b/lib/Transforms/Utils/Local.cpp
@@ -19,6 +19,7 @@
#include "llvm/Instructions.h"
#include "llvm/Intrinsics.h"
#include "llvm/IntrinsicInst.h"
+#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/DebugInfo.h"
#include "llvm/Target/TargetData.h"
@@ -177,14 +178,18 @@
return false;
}
+/// ~ValueDeletionListener - A trivial dtor, defined out of line to give the
+/// class a home.
+llvm::ValueDeletionListener::~ValueDeletionListener() {}
+
/// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a
/// trivially dead instruction, delete it. If that makes any of its operands
/// trivially dead, delete them too, recursively.
///
-/// If DeadInst is specified, the vector is filled with the instructions that
-/// are actually deleted.
+/// If a ValueDeletionListener is specified, it is notified of instructions that
+/// are actually deleted (before they are actually deleted).
void llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V,
- SmallVectorImpl<Instruction*> *DeadInst) {
+ ValueDeletionListener *VDL) {
Instruction *I = dyn_cast<Instruction>(V);
if (!I || !I->use_empty() || !isInstructionTriviallyDead(I))
return;
@@ -197,8 +202,8 @@
DeadInsts.pop_back();
// If the client wanted to know, tell it about deleted instructions.
- if (DeadInst)
- DeadInst->push_back(I);
+ if (VDL)
+ VDL->ValueWillBeDeleted(I);
// Null out all of the instruction's operands to see if any operand becomes
// dead as we go.
@@ -220,6 +225,38 @@
}
}
+/// RecursivelyDeleteDeadPHINode - If the specified value is an effectively
+/// dead PHI node, due to being a def-use chain of single-use nodes that
+/// either forms a cycle or is terminated by a trivially dead instruction,
+/// delete it. If that makes any of its operands trivially dead, delete them
+/// too, recursively.
+///
+/// If a ValueDeletionListener is specified, it is notified of instructions that
+/// are actually deleted (before they are actually deleted).
+void
+llvm::RecursivelyDeleteDeadPHINode(PHINode *PN, ValueDeletionListener *VDL) {
+
+ // We can remove a PHI if it is on a cycle in the def-use graph
+ // where each node in the cycle has degree one, i.e. only one use,
+ // and is an instruction with no side effects.
+ if (!PN->hasOneUse())
+ return;
+
+ SmallPtrSet<PHINode *, 4> PHIs;
+ PHIs.insert(PN);
+ for (Instruction *J = cast<Instruction>(*PN->use_begin());
+ J->hasOneUse() && !J->mayWriteToMemory();
+ J = cast<Instruction>(*J->use_begin()))
+ // If we find a PHI more than once, we're on a cycle that
+ // won't prove fruitful.
+ if (PHINode *JP = dyn_cast<PHINode>(J))
+ if (!PHIs.insert(cast<PHINode>(JP))) {
+ // Break the cycle and delete the PHI and its operands.
+ JP->replaceAllUsesWith(UndefValue::get(JP->getType()));
+ RecursivelyDeleteTriviallyDeadInstructions(JP, VDL);
+ break;
+ }
+}
//===----------------------------------------------------------------------===//
// Control Flow Graph Restructuring...