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.

llvm-svn: 70636
This commit is contained in:
Dan Gohman 2009-05-02 18:29:22 +00:00
parent cc9123424f
commit ff08995589
9 changed files with 121 additions and 51 deletions

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@ -25,6 +25,7 @@ namespace llvm {
class Instruction;
class Pass;
class AliasAnalysis;
class ValueDeletionListener;
/// DeleteDeadBlock - Delete the specified block, which must have no
/// predecessors.
@ -37,6 +38,12 @@ void DeleteDeadBlock(BasicBlock *BB);
/// when the block has exactly one predecessor.
void FoldSingleEntryPHINodes(BasicBlock *BB);
/// 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 DeleteDeadPHIs(BasicBlock *BB, ValueDeletionListener *VDL = 0);
/// MergeBlockIntoPredecessor - Attempts to merge a block into its predecessor,
/// if possible. The return value indicates success or failure.

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@ -50,15 +50,40 @@ bool ConstantFoldTerminator(BasicBlock *BB);
///
bool isInstructionTriviallyDead(Instruction *I);
/// ValueDeletionListener - A simple abstract interface for delivering
/// notifications when Values are deleted.
///
/// @todo Consider whether ValueDeletionListener can be made obsolete by
/// requiring clients to use CallbackVH instead.
class ValueDeletionListener {
public:
/// ValueWillBeDeleted - This method is called shortly before the specified
/// value will be deleted.
virtual void ValueWillBeDeleted(Value *V) = 0;
protected:
virtual ~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 RecursivelyDeleteTriviallyDeadInstructions(Value *V,
SmallVectorImpl<Instruction*> *DeadInst = 0);
ValueDeletionListener *VDL = 0);
/// 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 RecursivelyDeleteDeadPHINode(PHINode *PN,
ValueDeletionListener *VDL = 0);
//===----------------------------------------------------------------------===//
// Control Flow Graph Restructuring.

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@ -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 @@ ICmpInst *LoopStrengthReduce::ChangeCompareStride(Loop *L, ICmpInst *Cond,
CondUse = &IVUsesByStride[*NewStride].Users.back();
CondStride = NewStride;
++NumEliminated;
Changed = true;
}
return Cond;
@ -2501,44 +2503,21 @@ bool LoopStrengthReduce::runOnLoop(Loop *L, LPPassManager &LPM) {
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;
// 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) {}
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;
}
}
DeleteTriviallyDeadInstructions();
virtual void ValueWillBeDeleted(Value *V) {
SE.deleteValueFromRecords(V);
}
} VDL(*SE);
DeleteDeadPHIs(L->getHeader(), &VDL);
return Changed;
}

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@ -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 @@ void llvm::FoldSingleEntryPHINodes(BasicBlock *BB) {
}
/// 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) {

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@ -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 @@ bool llvm::isInstructionTriviallyDead(Instruction *I) {
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 @@ void llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V,
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 @@ void llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V,
}
}
/// 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...

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@ -1,5 +1,4 @@
; RUN: llvm-as < %s | llc -mtriple=arm-apple-darwin9
; RUN: llvm-as < %s | llc -mtriple=arm-apple-darwin9 -stats |& grep asm-printer | grep 186
; RUN: llvm-as < %s | llc -mtriple=arm-apple-darwin9 -stats |& grep asm-printer | grep 184
%"struct.Adv5::Ekin<3>" = type <{ i8 }>
%"struct.Adv5::X::Energyflux<3>" = type { double }

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@ -17,6 +17,7 @@ bb554: ; preds = %bb554, %entry
%tmp555 = and <2 x i32> %1, < i32 -1, i32 0 > ; <<2 x i32>> [#uses=1]
%2 = bitcast <2 x i32> %tmp555 to <1 x i64> ; <<1 x i64>> [#uses=1]
%3 = call <1 x i64> @llvm.x86.mmx.psrli.q(<1 x i64> %0, i32 32) nounwind readnone ; <<1 x i64>> [#uses=1]
store <1 x i64> %sum.0.reg2mem.0, <1 x i64>* null
%tmp558 = add <1 x i64> %sum.0.reg2mem.0, %2 ; <<1 x i64>> [#uses=1]
%4 = call <1 x i64> @llvm.x86.mmx.psrli.q(<1 x i64> %tmp558, i32 32) nounwind readnone ; <<1 x i64>> [#uses=1]
%tmp562 = add <1 x i64> %4, %3 ; <<1 x i64>> [#uses=1]

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@ -14,6 +14,8 @@ bb: ; preds = %bb, %entry
%2 = tail call double @sin(double %k.0.reg2mem.0) nounwind readonly ; <double> [#uses=1]
%3 = mul double 0.000000e+00, %2 ; <double> [#uses=1]
%4 = fdiv double 1.000000e+00, %3 ; <double> [#uses=1]
store double %Flint.0.reg2mem.0, double* null
store double %twoThrd.0.reg2mem.0, double* null
%5 = add double %4, %Flint.0.reg2mem.0 ; <double> [#uses=1]
%6 = add double %k.0.reg2mem.0, 1.000000e+00 ; <double> [#uses=1]
br label %bb

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@ -1,4 +1,4 @@
; RUN: llvm-as < %s | opt -loop-reduce | llvm-dis | grep {phi\\>} | count 14
; RUN: llvm-as < %s | opt -loop-reduce | llvm-dis | grep {phi\\>} | count 10
; PR2570
target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:32:32"