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If a loop termination compare instruction is the only use of its stride, 

and the compaison is against a constant value, try eliminate the stride
by moving the compare instruction to another stride and change its
constant operand accordingly. e.g.

loop:
...
v1 = v1 + 3
v2 = v2 + 1
if (v2 < 10) goto loop
=>
loop:
...
v1 = v1 + 3
if (v1 < 30) goto loop

llvm-svn: 43336
This commit is contained in:
Evan Cheng 2007-10-25 09:11:16 +00:00
parent ac72db5dbe
commit 133694db06
3 changed files with 249 additions and 34 deletions
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197
llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
View File

@ -39,9 +39,10 @@
#include <set>
using namespace llvm;
STATISTIC(NumReduced , "Number of GEPs strength reduced");
STATISTIC(NumInserted, "Number of PHIs inserted");
STATISTIC(NumVariable, "Number of PHIs with variable strides");
STATISTIC(NumReduced , "Number of GEPs strength reduced");
STATISTIC(NumInserted, "Number of PHIs inserted");
STATISTIC(NumVariable, "Number of PHIs with variable strides");
STATISTIC(NumEliminated , "Number of strides eliminated");
namespace {
@ -170,18 +171,17 @@ private:
bool AddUsersIfInteresting(Instruction *I, Loop *L,
std::set<Instruction*> &Processed);
SCEVHandle GetExpressionSCEV(Instruction *E, Loop *L);
ICmpInst *ChangeCompareStride(Loop *L, ICmpInst *Cond,
IVStrideUse* &CondUse,
const SCEVHandle* &CondStride);
void OptimizeIndvars(Loop *L);
bool FindIVForUser(ICmpInst *Cond, IVStrideUse *&CondUse,
const SCEVHandle *&CondStride);
unsigned CheckForIVReuse(bool, const SCEVHandle&,
IVExpr&, const Type*,
const std::vector<BasedUser>& UsersToProcess);
bool ValidStride(bool, int64_t,
const std::vector<BasedUser>& UsersToProcess);
void StrengthReduceStridedIVUsers(const SCEVHandle &Stride,
IVUsersOfOneStride &Uses,
Loop *L, bool isOnlyStride);
@ -981,8 +981,6 @@ unsigned LoopStrengthReduce::CheckForIVReuse(bool HasBaseReg,
const SCEVHandle &Stride,
IVExpr &IV, const Type *Ty,
const std::vector<BasedUser>& UsersToProcess) {
if (!TLI) return 0;
if (SCEVConstant *SC = dyn_cast<SCEVConstant>(Stride)) {
int64_t SInt = SC->getValue()->getSExtValue();
if (SInt == 1) return 0;
@ -1039,6 +1037,10 @@ void LoopStrengthReduce::StrengthReduceStridedIVUsers(const SCEVHandle &Stride,
IVUsersOfOneStride &Uses,
Loop *L,
bool isOnlyStride) {
// If all the users are moved to another stride, then there is nothing to do.
if (Uses.Users.size() == 0)
return;
// Transform our list of users and offsets to a bit more complex table. In
// this new vector, each 'BasedUser' contains 'Base' the base of the
// strided accessas well as the old information from Uses. We progressively
@ -1377,6 +1379,154 @@ bool LoopStrengthReduce::FindIVForUser(ICmpInst *Cond, IVStrideUse *&CondUse,
return false;
}
namespace {
// Constant strides come first which in turns are sorted by their absolute
// values. If absolute values are the same, then positive strides comes first.
// e.g.
// 4, -1, X, 1, 2 ==> 1, -1, 2, 4, X
struct StrideCompare {
bool operator()(const SCEVHandle &LHS, const SCEVHandle &RHS) {
SCEVConstant *LHSC = dyn_cast<SCEVConstant>(LHS);
SCEVConstant *RHSC = dyn_cast<SCEVConstant>(RHS);
if (LHSC && RHSC) {
int64_t LV = LHSC->getValue()->getSExtValue();
int64_t RV = RHSC->getValue()->getSExtValue();
uint64_t ALV = (LV < 0) ? -LV : LV;
uint64_t ARV = (RV < 0) ? -RV : RV;
if (ALV == ARV)
return LV > RV;
else
return ALV < ARV;
}
return (LHSC && !RHSC);
}
};
}
/// ChangeCompareStride - If a loop termination compare instruction is the
/// only use of its stride, and the compaison is against a constant value,
/// try eliminate the stride by moving the compare instruction to another
/// stride and change its constant operand accordingly. e.g.
///
/// loop:
/// ...
/// v1 = v1 + 3
/// v2 = v2 + 1
/// if (v2 < 10) goto loop
/// =>
/// loop:
/// ...
/// v1 = v1 + 3
/// if (v1 < 30) goto loop
ICmpInst *LoopStrengthReduce::ChangeCompareStride(Loop *L, ICmpInst *Cond,
IVStrideUse* &CondUse,
const SCEVHandle* &CondStride) {
if (StrideOrder.size() < 2 ||
IVUsesByStride[*CondStride].Users.size() != 1)
return Cond;
// FIXME: loosen this restriction?
if (!isa<SCEVConstant>(CondUse->Offset))
return Cond;
const SCEVConstant *SC = dyn_cast<SCEVConstant>(*CondStride);
if (!SC) return Cond;
ConstantInt *C = dyn_cast<ConstantInt>(Cond->getOperand(1));
if (!C) return Cond;
ICmpInst::Predicate Predicate = Cond->getPredicate();
bool isSigned = ICmpInst::isSignedPredicate(Predicate);
int64_t CmpSSInt = SC->getValue()->getSExtValue();
int64_t CmpVal = C->getValue().getSExtValue();
uint64_t SignBit = 1ULL << (C->getValue().getBitWidth()-1);
int64_t NewCmpVal = CmpVal;
SCEVHandle *NewStride = NULL;
Value *NewIncV = NULL;
int64_t Scale = 1;
const Type *CmpTy = C->getType();
const Type *NewCmpTy = NULL;
// Look for a suitable stride / iv as replacement.
std::stable_sort(StrideOrder.begin(), StrideOrder.end(), StrideCompare());
for (unsigned i = 0, e = StrideOrder.size(); i != e; ++i) {
std::map<SCEVHandle, IVUsersOfOneStride>::iterator SI =
IVUsesByStride.find(StrideOrder[i]);
if (!isa<SCEVConstant>(SI->first))
continue;
int64_t SSInt = cast<SCEVConstant>(SI->first)->getValue()->getSExtValue();
if (abs(SSInt) < abs(CmpSSInt) && (CmpSSInt % SSInt) == 0) {
Scale = CmpSSInt / SSInt;
NewCmpVal = CmpVal / Scale;
} else if (abs(SSInt) > abs(CmpSSInt) && (SSInt % CmpSSInt) == 0) {
Scale = SSInt / CmpSSInt;
NewCmpVal = CmpVal * Scale;
} else
continue;
// Watch out for overflow.
if (isSigned && (CmpVal & SignBit) != (NewCmpVal & SignBit))
NewCmpVal = CmpVal;
if (NewCmpVal != CmpVal) {
// Pick the best iv to use trying to avoid a cast.
NewIncV = NULL;
for (std::vector<IVStrideUse>::iterator UI = SI->second.Users.begin(),
E = SI->second.Users.end(); UI != E; ++UI) {
// if (!isa<SCEVConstant>(UI->Offset))
// continue;
NewIncV = UI->OperandValToReplace;
if (NewIncV->getType() == CmpTy)
break;
}
if (!NewIncV) {
NewCmpVal = CmpVal;
continue;
}
// FIXME: allow reuse of iv of a smaller type?
NewCmpTy = NewIncV->getType();
if (!CmpTy->canLosslesslyBitCastTo(NewCmpTy) &&
!(isa<PointerType>(NewCmpTy) &&
CmpTy->canLosslesslyBitCastTo(UIntPtrTy))) {
NewCmpVal = CmpVal;
continue;
}
// If scale is negative, use inverse predicate unless it's testing
// for equality.
if (Scale < 0 && !Cond->isEquality())
Predicate = ICmpInst::getInversePredicate(Predicate);
NewStride = &StrideOrder[i];
break;
}
}
if (NewCmpVal != CmpVal) {
// Create a new compare instruction using new stride / iv.
ICmpInst *OldCond = Cond;
Value *RHS = ConstantInt::get(C->getType(), NewCmpVal);
// Both sides of a ICmpInst must be of the same type.
if (NewCmpTy != CmpTy) {
if (isa<PointerType>(NewCmpTy) && !isa<PointerType>(CmpTy))
RHS= SCEVExpander::InsertCastOfTo(Instruction::IntToPtr, RHS, NewCmpTy);
else
RHS = SCEVExpander::InsertCastOfTo(Instruction::BitCast, RHS, NewCmpTy);
}
Cond = new ICmpInst(Predicate, NewIncV, RHS);
Cond->setName(L->getHeader()->getName() + ".termcond");
OldCond->getParent()->getInstList().insert(OldCond, Cond);
OldCond->replaceAllUsesWith(Cond);
OldCond->eraseFromParent();
IVUsesByStride[*CondStride].Users.pop_back();
SCEVHandle NewOffset = SE->getMulExpr(CondUse->Offset,
SE->getConstant(ConstantInt::get(CondUse->Offset->getType(), Scale)));
IVUsesByStride[*NewStride].addUser(NewOffset, Cond, NewIncV);
CondUse = &IVUsesByStride[*NewStride].Users.back();
CondStride = NewStride;
++NumEliminated;
}
return Cond;
}
// OptimizeIndvars - Now that IVUsesByStride is set up with all of the indvar
// uses in the loop, look to see if we can eliminate some, in favor of using
// common indvars for the different uses.
@ -1403,7 +1553,10 @@ void LoopStrengthReduce::OptimizeIndvars(Loop *L) {
if (!FindIVForUser(Cond, CondUse, CondStride))
return; // setcc doesn't use the IV.
// If possible, change stride and operands of the compare instruction to
// eliminate one stride.
Cond = ChangeCompareStride(L, Cond, CondUse, CondStride);
// It's possible for the setcc instruction to be anywhere in the loop, and
// possible for it to have multiple users. If it is not immediately before
@ -1431,30 +1584,6 @@ void LoopStrengthReduce::OptimizeIndvars(Loop *L) {
CondUse->isUseOfPostIncrementedValue = true;
}
namespace {
// Constant strides come first which in turns are sorted by their absolute
// values. If absolute values are the same, then positive strides comes first.
// e.g.
// 4, -1, X, 1, 2 ==> 1, -1, 2, 4, X
struct StrideCompare {
bool operator()(const SCEVHandle &LHS, const SCEVHandle &RHS) {
SCEVConstant *LHSC = dyn_cast<SCEVConstant>(LHS);
SCEVConstant *RHSC = dyn_cast<SCEVConstant>(RHS);
if (LHSC && RHSC) {
int64_t LV = LHSC->getValue()->getSExtValue();
int64_t RV = RHSC->getValue()->getSExtValue();
uint64_t ALV = (LV < 0) ? -LV : LV;
uint64_t ARV = (RV < 0) ? -RV : RV;
if (ALV == ARV)
return LV > RV;
else
return ALV < ARV;
}
return (LHSC && !RHSC);
}
};
}
bool LoopStrengthReduce::runOnLoop(Loop *L, LPPassManager &LPM) {
LI = &getAnalysis<LoopInfo>();

37
llvm/test/CodeGen/X86/loop-strength-reduce3.ll Normal file
View File

@ -0,0 +1,37 @@
; RUN: llvm-as < %s | llc -march=x86 | grep cmp | grep 240
; RUN: llvm-as < %s | llc -march=x86 | grep inc | count 1
define i32 @foo(i32 %A, i32 %B, i32 %C, i32 %D) {
entry:
%tmp2955 = icmp sgt i32 %C, 0 ; <i1> [#uses=1]
br i1 %tmp2955, label %bb26.outer.us, label %bb40.split
bb26.outer.us: ; preds = %bb26.bb32_crit_edge.us, %entry
%i.044.0.ph.us = phi i32 [ 0, %entry ], [ %indvar.next57, %bb26.bb32_crit_edge.us ] ; <i32> [#uses=2]
%k.1.ph.us = phi i32 [ 0, %entry ], [ %k.0.us, %bb26.bb32_crit_edge.us ] ; <i32> [#uses=1]
%tmp3.us = mul i32 %i.044.0.ph.us, 6 ; <i32> [#uses=1]
br label %bb1.us
bb1.us: ; preds = %bb1.us, %bb26.outer.us
%j.053.us = phi i32 [ 0, %bb26.outer.us ], [ %tmp25.us, %bb1.us ] ; <i32> [#uses=2]
%k.154.us = phi i32 [ %k.1.ph.us, %bb26.outer.us ], [ %k.0.us, %bb1.us ] ; <i32> [#uses=1]
%tmp5.us = add i32 %tmp3.us, %j.053.us ; <i32> [#uses=1]
%tmp7.us = shl i32 %D, %tmp5.us ; <i32> [#uses=2]
%tmp9.us = icmp eq i32 %tmp7.us, %B ; <i1> [#uses=1]
%tmp910.us = zext i1 %tmp9.us to i32 ; <i32> [#uses=1]
%tmp12.us = and i32 %tmp7.us, %A ; <i32> [#uses=1]
%tmp19.us = and i32 %tmp12.us, %tmp910.us ; <i32> [#uses=1]
%k.0.us = add i32 %tmp19.us, %k.154.us ; <i32> [#uses=3]
%tmp25.us = add i32 %j.053.us, 1 ; <i32> [#uses=2]
%tmp29.us = icmp slt i32 %tmp25.us, %C ; <i1> [#uses=1]
br i1 %tmp29.us, label %bb1.us, label %bb26.bb32_crit_edge.us
bb26.bb32_crit_edge.us: ; preds = %bb1.us
%indvar.next57 = add i32 %i.044.0.ph.us, 1 ; <i32> [#uses=2]
%exitcond = icmp eq i32 %indvar.next57, 40 ; <i1> [#uses=1]
br i1 %exitcond, label %bb40.split, label %bb26.outer.us
bb40.split: ; preds = %bb26.bb32_crit_edge.us, %entry
%k.1.lcssa.lcssa.us-lcssa = phi i32 [ %k.0.us, %bb26.bb32_crit_edge.us ], [ 0, %entry ] ; <i32> [#uses=1]
ret i32 %k.1.lcssa.lcssa.us-lcssa
}

49
llvm/test/CodeGen/X86/loop-strength-reduce4.ll Normal file
View File

@ -0,0 +1,49 @@
; RUN: llvm-as < %s | llc -march=x86 | grep cmp | grep 64
; RUN: llvm-as < %s | llc -march=x86 | not grep inc
@state = external global [0 x i32] ; <[0 x i32]*> [#uses=4]
@S = external global [0 x i32] ; <[0 x i32]*> [#uses=4]
define i32 @foo() {
entry:
br label %bb
bb: ; preds = %bb, %entry
%indvar = phi i32 [ 0, %entry ], [ %indvar.next, %bb ] ; <i32> [#uses=2]
%t.063.0 = phi i32 [ 0, %entry ], [ %tmp47, %bb ] ; <i32> [#uses=1]
%j.065.0 = shl i32 %indvar, 2 ; <i32> [#uses=4]
%tmp3 = getelementptr [0 x i32]* @state, i32 0, i32 %j.065.0 ; <i32*> [#uses=2]
%tmp4 = load i32* %tmp3, align 4 ; <i32> [#uses=1]
%tmp6 = getelementptr [0 x i32]* @S, i32 0, i32 %t.063.0 ; <i32*> [#uses=1]
%tmp7 = load i32* %tmp6, align 4 ; <i32> [#uses=1]
%tmp8 = xor i32 %tmp7, %tmp4 ; <i32> [#uses=2]
store i32 %tmp8, i32* %tmp3, align 4
%tmp1378 = or i32 %j.065.0, 1 ; <i32> [#uses=1]
%tmp16 = getelementptr [0 x i32]* @state, i32 0, i32 %tmp1378 ; <i32*> [#uses=2]
%tmp17 = load i32* %tmp16, align 4 ; <i32> [#uses=1]
%tmp19 = getelementptr [0 x i32]* @S, i32 0, i32 %tmp8 ; <i32*> [#uses=1]
%tmp20 = load i32* %tmp19, align 4 ; <i32> [#uses=1]
%tmp21 = xor i32 %tmp20, %tmp17 ; <i32> [#uses=2]
store i32 %tmp21, i32* %tmp16, align 4
%tmp2680 = or i32 %j.065.0, 2 ; <i32> [#uses=1]
%tmp29 = getelementptr [0 x i32]* @state, i32 0, i32 %tmp2680 ; <i32*> [#uses=2]
%tmp30 = load i32* %tmp29, align 4 ; <i32> [#uses=1]
%tmp32 = getelementptr [0 x i32]* @S, i32 0, i32 %tmp21 ; <i32*> [#uses=1]
%tmp33 = load i32* %tmp32, align 4 ; <i32> [#uses=1]
%tmp34 = xor i32 %tmp33, %tmp30 ; <i32> [#uses=2]
store i32 %tmp34, i32* %tmp29, align 4
%tmp3982 = or i32 %j.065.0, 3 ; <i32> [#uses=1]
%tmp42 = getelementptr [0 x i32]* @state, i32 0, i32 %tmp3982 ; <i32*> [#uses=2]
%tmp43 = load i32* %tmp42, align 4 ; <i32> [#uses=1]
%tmp45 = getelementptr [0 x i32]* @S, i32 0, i32 %tmp34 ; <i32*> [#uses=1]
%tmp46 = load i32* %tmp45, align 4 ; <i32> [#uses=1]
%tmp47 = xor i32 %tmp46, %tmp43 ; <i32> [#uses=3]
store i32 %tmp47, i32* %tmp42, align 4
%indvar.next = add i32 %indvar, 1 ; <i32> [#uses=2]
%exitcond = icmp eq i32 %indvar.next, 4 ; <i1> [#uses=1]
br i1 %exitcond, label %bb57, label %bb
bb57: ; preds = %bb
%tmp59 = and i32 %tmp47, 255 ; <i32> [#uses=1]
ret i32 %tmp59
}