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SCEVExpander fixes. Affects LSR and indvars.

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LSR has gradually been improved to more aggressively reuse existing code, particularly existing phi cycles. This exposed problems with the SCEVExpander's sloppy treatment of its insertion point. I applied some rigor to the insertion point problem that will hopefully avoid an endless bug cycle in this area. Changes:

- Always used properlyDominates to check safe code hoisting.

- The insertion point provided to SCEV is now considered a lower bound. This is usually a block terminator or the use itself. Under no cirumstance may SCEVExpander insert below this point.

- LSR is reponsible for finding a "canonical" insertion point across expansion of different expressions.

- Robust logic to determine whether IV increments are in "expanded" form and/or can be safely hoisted above some insertion point.

Fixes PR11783: SCEVExpander assert.

llvm-svn: 148535
This commit is contained in:
Andrew Trick 2012-01-20 07:41:13 +00:00
parent e2d3f3060d
commit be3e9530e1
6 changed files with 203 additions and 146 deletions
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6
include/llvm/Analysis/Dominators.h
View File

@ -753,6 +753,12 @@ public:
// special checks necessary if A and B are in the same basic block.
bool dominates(const Instruction *A, const Instruction *B) const;
/// properlyDominates - Use this instead of dominates() to determine whether a
/// user of A can be hoisted above B.
bool properlyDominates(const Instruction *A, const Instruction *B) const {
return A != B && dominates(A, B);
}
bool properlyDominates(const DomTreeNode *A, const DomTreeNode *B) const {
return DT->properlyDominates(A, B);
}

23
include/llvm/Analysis/ScalarEvolutionExpander.h
View File

@ -114,9 +114,12 @@ namespace llvm {
/// starts at zero and steps by one on each iteration.
PHINode *getOrInsertCanonicalInductionVariable(const Loop *L, Type *Ty);
/// hoistStep - Utility for hoisting an IV increment.
static bool hoistStep(Instruction *IncV, Instruction *InsertPos,
const DominatorTree *DT);
/// getIVIncOperand - Return the induction variable increment's IV operand.
Instruction *getIVIncOperand(Instruction *IncV, Instruction *InsertPos,
bool allowScale);
/// hoistIVInc - Utility for hoisting an IV increment.
bool hoistIVInc(Instruction *IncV, Instruction *InsertPos);
/// replaceCongruentIVs - replace congruent phis with their most canonical
/// representative. Return the number of phis eliminated.
@ -169,6 +172,13 @@ namespace llvm {
Builder.ClearInsertionPoint();
}
/// isInsertedInstruction - Return true if the specified instruction was
/// inserted by the code rewriter. If so, the client should not modify the
/// instruction.
bool isInsertedInstruction(Instruction *I) const {
return InsertedValues.count(I) || InsertedPostIncValues.count(I);
}
void setChainedPhi(PHINode *PN) { ChainedPhis.insert(PN); }
private:
@ -205,13 +215,6 @@ namespace llvm {
/// result will be expanded to have that type, with a cast if necessary.
Value *expandCodeFor(const SCEV *SH, Type *Ty = 0);
/// isInsertedInstruction - Return true if the specified instruction was
/// inserted by the code rewriter. If so, the client should not modify the
/// instruction.
bool isInsertedInstruction(Instruction *I) const {
return InsertedValues.count(I) || InsertedPostIncValues.count(I);
}
/// getRelevantLoop - Determine the most "relevant" loop for the given SCEV.
const Loop *getRelevantLoop(const SCEV *);

249
lib/Analysis/ScalarEvolutionExpander.cpp
View File

@ -38,8 +38,11 @@ Value *SCEVExpander::ReuseOrCreateCast(Value *V, Type *Ty,
if (U->getType() == Ty)
if (CastInst *CI = dyn_cast<CastInst>(U))
if (CI->getOpcode() == Op) {
// If the cast isn't where we want it, fix it.
if (BasicBlock::iterator(CI) != IP) {
// If the cast isn't where we want it, fix it. All new or reused
// instructions must strictly dominate the Builder's InsertPt to
// ensure that the expression's expansion dominates its uses.
if (BasicBlock::iterator(CI) != IP
|| IP == Builder.GetInsertPoint()) {
// Create a new cast, and leave the old cast in place in case
// it is being used as an insert point. Clear its operand
// so that it doesn't hold anything live.
@ -867,6 +870,94 @@ bool SCEVExpander::isNormalAddRecExprPHI(PHINode *PN, Instruction *IncV,
return isNormalAddRecExprPHI(PN, IncV, L);
}
/// getIVIncOperand returns an induction variable increment's induction
/// variable operand.
///
/// If allowScale is set, any type of GEP is allowed as long as the nonIV
/// operands dominate InsertPos.
///
/// If allowScale is not set, ensure that a GEP increment conforms to one of the
/// simple patterns generated by getAddRecExprPHILiterally and
/// expandAddtoGEP. If the pattern isn't recognized, return NULL.
Instruction *SCEVExpander::getIVIncOperand(Instruction *IncV,
Instruction *InsertPos,
bool allowScale) {
if (IncV == InsertPos)
return NULL;
switch (IncV->getOpcode()) {
default:
return NULL;
// Check for a simple Add/Sub or GEP of a loop invariant step.
case Instruction::Add:
case Instruction::Sub: {
Instruction *OInst = dyn_cast<Instruction>(IncV->getOperand(1));
if (!OInst || SE.DT->properlyDominates(OInst, InsertPos))
return dyn_cast<Instruction>(IncV->getOperand(0));
return NULL;
}
case Instruction::BitCast:
return dyn_cast<Instruction>(IncV->getOperand(0));
case Instruction::GetElementPtr:
for (Instruction::op_iterator I = IncV->op_begin()+1, E = IncV->op_end();
I != E; ++I) {
if (isa<Constant>(*I))
continue;
if (Instruction *OInst = dyn_cast<Instruction>(*I)) {
if (!SE.DT->properlyDominates(OInst, InsertPos))
return NULL;
}
if (allowScale) {
// allow any kind of GEP as long as it can be hoisted.
continue;
}
// This must be a pointer addition of constants (pretty), which is already
// handled, or some number of address-size elements (ugly). Ugly geps
// have 2 operands. i1* is used by the expander to represent an
// address-size element.
if (IncV->getNumOperands() != 2)
return NULL;
unsigned AS = cast<PointerType>(IncV->getType())->getAddressSpace();
if (IncV->getType() != Type::getInt1PtrTy(SE.getContext(), AS)
&& IncV->getType() != Type::getInt8PtrTy(SE.getContext(), AS))
return NULL;
break;
}
return dyn_cast<Instruction>(IncV->getOperand(0));
}
}
/// hoistStep - Attempt to hoist a simple IV increment above InsertPos to make
/// it available to other uses in this loop. Recursively hoist any operands,
/// until we reach a value that dominates InsertPos.
bool SCEVExpander::hoistIVInc(Instruction *IncV, Instruction *InsertPos) {
if (SE.DT->properlyDominates(IncV, InsertPos))
return true;
// InsertPos must itself dominate IncV so that IncV's new position satisfies
// its existing users.
if (!SE.DT->dominates(InsertPos->getParent(), IncV->getParent()))
return false;
// Check that the chain of IV operands leading back to Phi can be hoisted.
SmallVector<Instruction*, 4> IVIncs;
for(;;) {
Instruction *Oper = getIVIncOperand(IncV, InsertPos, /*allowScale*/true);
if (!Oper)
return false;
// IncV is safe to hoist.
IVIncs.push_back(IncV);
IncV = Oper;
if (SE.DT->properlyDominates(IncV, InsertPos))
break;
}
for (SmallVectorImpl<Instruction*>::reverse_iterator I = IVIncs.rbegin(),
E = IVIncs.rend(); I != E; ++I) {
(*I)->moveBefore(InsertPos);
}
return true;
}
/// Determine if this cyclic phi is in a form that would have been generated by
/// LSR. We don't care if the phi was actually expanded in this pass, as long
/// as it is in a low-cost form, for example, no implied multiplication. This
@ -874,54 +965,13 @@ bool SCEVExpander::isNormalAddRecExprPHI(PHINode *PN, Instruction *IncV,
/// expandAddtoGEP.
bool SCEVExpander::isExpandedAddRecExprPHI(PHINode *PN, Instruction *IncV,
const Loop *L) {
if (ChainedPhis.count(PN))
return true;
switch (IncV->getOpcode()) {
// Check for a simple Add/Sub or GEP of a loop invariant step.
case Instruction::Add:
case Instruction::Sub:
return IncV->getOperand(0) == PN
&& L->isLoopInvariant(IncV->getOperand(1));
case Instruction::BitCast:
IncV = dyn_cast<GetElementPtrInst>(IncV->getOperand(0));
if (!IncV)
return false;
// fall-thru to GEP handling
case Instruction::GetElementPtr: {
// This must be a pointer addition of constants (pretty) or some number of
// address-size elements (ugly).
for (Instruction::op_iterator I = IncV->op_begin()+1, E = IncV->op_end();
I != E; ++I) {
if (isa<Constant>(*I))
continue;
// ugly geps have 2 operands.
// i1* is used by the expander to represent an address-size element.
if (IncV->getNumOperands() != 2)
return false;
unsigned AS = cast<PointerType>(IncV->getType())->getAddressSpace();
if (IncV->getType() != Type::getInt1PtrTy(SE.getContext(), AS)
&& IncV->getType() != Type::getInt8PtrTy(SE.getContext(), AS))
return false;
// Ensure the operands dominate the insertion point. I don't know of a
// case when this would not be true, so this is somewhat untested.
if (L == IVIncInsertLoop) {
for (User::op_iterator OI = IncV->op_begin()+1,
OE = IncV->op_end(); OI != OE; ++OI)
if (Instruction *OInst = dyn_cast<Instruction>(OI))
if (!SE.DT->dominates(OInst, IVIncInsertPos))
return false;
}
break;
}
IncV = dyn_cast<Instruction>(IncV->getOperand(0));
if (IncV && IncV->getOpcode() == Instruction::BitCast)
IncV = dyn_cast<Instruction>(IncV->getOperand(0));
return IncV == PN;
}
default:
return false;
for(Instruction *IVOper = IncV;
(IVOper = getIVIncOperand(IVOper, L->getLoopPreheader()->getTerminator(),
/*allowScale=*/false));) {
if (IVOper == PN)
return true;
}
return false;
}
/// expandIVInc - Expand an IV increment at Builder's current InsertPos.
@ -981,26 +1031,28 @@ SCEVExpander::getAddRecExprPHILiterally(const SCEVAddRecExpr *Normalized,
if (LSRMode) {
if (!isExpandedAddRecExprPHI(PN, IncV, L))
continue;
if (L == IVIncInsertLoop && !hoistIVInc(IncV, IVIncInsertPos))
continue;
}
else {
if (!isNormalAddRecExprPHI(PN, IncV, L))
continue;
if (L == IVIncInsertLoop)
do {
if (SE.DT->dominates(IncV, IVIncInsertPos))
break;
// Make sure the increment is where we want it. But don't move it
// down past a potential existing post-inc user.
IncV->moveBefore(IVIncInsertPos);
IVIncInsertPos = IncV;
IncV = cast<Instruction>(IncV->getOperand(0));
} while (IncV != PN);
}
// Ok, the add recurrence looks usable.
// Remember this PHI, even in post-inc mode.
InsertedValues.insert(PN);
// Remember the increment.
rememberInstruction(IncV);
if (L == IVIncInsertLoop)
do {
if (SE.DT->dominates(IncV, IVIncInsertPos))
break;
// Make sure the increment is where we want it. But don't move it
// down past a potential existing post-inc user.
IncV->moveBefore(IVIncInsertPos);
IVIncInsertPos = IncV;
IncV = cast<Instruction>(IncV->getOperand(0));
} while (IncV != PN);
return PN;
}
}
@ -1404,10 +1456,7 @@ Value *SCEVExpander::visitUMaxExpr(const SCEVUMaxExpr *S) {
}
Value *SCEVExpander::expandCodeFor(const SCEV *SH, Type *Ty,
Instruction *I) {
BasicBlock::iterator IP = I;
while (isInsertedInstruction(IP) || isa<DbgInfoIntrinsic>(IP))
++IP;
Instruction *IP) {
Builder.SetInsertPoint(IP->getParent(), IP);
return expandCodeFor(SH, Ty);
}
@ -1445,8 +1494,11 @@ Value *SCEVExpander::expand(const SCEV *S) {
// there) so that it is guaranteed to dominate any user inside the loop.
if (L && SE.hasComputableLoopEvolution(S, L) && !PostIncLoops.count(L))
InsertPt = L->getHeader()->getFirstInsertionPt();
while (isInsertedInstruction(InsertPt) || isa<DbgInfoIntrinsic>(InsertPt))
while (InsertPt != Builder.GetInsertPoint()
&& (isInsertedInstruction(InsertPt)
|| isa<DbgInfoIntrinsic>(InsertPt))) {
InsertPt = llvm::next(BasicBlock::iterator(InsertPt));
}
break;
}
@ -1481,23 +1533,9 @@ void SCEVExpander::rememberInstruction(Value *I) {
InsertedPostIncValues.insert(I);
else
InsertedValues.insert(I);
// If we just claimed an existing instruction and that instruction had
// been the insert point, adjust the insert point forward so that
// subsequently inserted code will be dominated.
if (Builder.GetInsertPoint() == I) {
BasicBlock::iterator It = cast<Instruction>(I);
do { ++It; } while (isInsertedInstruction(It) ||
isa<DbgInfoIntrinsic>(It));
Builder.SetInsertPoint(Builder.GetInsertBlock(), It);
}
}
void SCEVExpander::restoreInsertPoint(BasicBlock *BB, BasicBlock::iterator I) {
// If we acquired more instructions since the old insert point was saved,
// advance past them.
while (isInsertedInstruction(I) || isa<DbgInfoIntrinsic>(I)) ++I;
Builder.SetInsertPoint(BB, I);
}
@ -1525,49 +1563,6 @@ SCEVExpander::getOrInsertCanonicalInductionVariable(const Loop *L,
return V;
}
/// hoistStep - Attempt to hoist an IV increment above a potential use.
///
/// To successfully hoist, two criteria must be met:
/// - IncV operands dominate InsertPos and
/// - InsertPos dominates IncV
///
/// Meeting the second condition means that we don't need to check all of IncV's
/// existing uses (it's moving up in the domtree).
///
/// This does not yet recursively hoist the operands, although that would
/// not be difficult.
///
/// This does not require a SCEVExpander instance and could be replaced by a
/// general code-insertion helper.
bool SCEVExpander::hoistStep(Instruction *IncV, Instruction *InsertPos,
const DominatorTree *DT) {
// Phi nodes are strangely positional but don't follow normal rules for
// instruction dominance. Handle them immediately.
if (isa<PHINode>(InsertPos))
return isa<PHINode>(IncV);
else if (isa<PHINode>(IncV))
return false;
if (DT->dominates(IncV, InsertPos))
return true;
if (!DT->dominates(InsertPos->getParent(), IncV->getParent()))
return false;
if (IncV->mayHaveSideEffects())
return false;
// Attempt to hoist IncV
for (User::op_iterator OI = IncV->op_begin(), OE = IncV->op_end();
OI != OE; ++OI) {
Instruction *OInst = dyn_cast<Instruction>(OI);
if (OInst && (OInst == InsertPos || !DT->dominates(OInst, InsertPos)))
return false;
}
IncV->moveBefore(InsertPos);
return true;
}
/// Sort values by integer width for replaceCongruentIVs.
static bool width_descending(Value *lhs, Value *rhs) {
// Put pointers at the back and make sure pointer < pointer = false.
@ -1632,10 +1627,13 @@ unsigned SCEVExpander::replaceCongruentIVs(Loop *L, const DominatorTree *DT,
cast<Instruction>(Phi->getIncomingValueForBlock(LatchBlock));
// If this phi has the same width but is more canonical, replace the
// original with it.
// original with it. As part of the "more canonical" determination,
// respect a prior decision to use an IV chain.
if (OrigPhiRef->getType() == Phi->getType()
&& !isExpandedAddRecExprPHI(OrigPhiRef, OrigInc, L)
&& isExpandedAddRecExprPHI(Phi, IsomorphicInc, L)) {
&& !(ChainedPhis.count(Phi)
|| isExpandedAddRecExprPHI(OrigPhiRef, OrigInc, L))
&& (ChainedPhis.count(Phi)
|| isExpandedAddRecExprPHI(Phi, IsomorphicInc, L))) {
std::swap(OrigPhiRef, Phi);
std::swap(OrigInc, IsomorphicInc);
}
@ -1649,7 +1647,8 @@ unsigned SCEVExpander::replaceCongruentIVs(Loop *L, const DominatorTree *DT,
IsomorphicInc->getType());
if (OrigInc != IsomorphicInc
&& TruncExpr == SE.getSCEV(IsomorphicInc)
&& hoistStep(OrigInc, IsomorphicInc, DT)) {
&& ((isa<PHINode>(OrigInc) && isa<PHINode>(IsomorphicInc))
|| hoistIVInc(OrigInc, IsomorphicInc))) {
DEBUG_WITH_TYPE(DebugType, dbgs()
<< "INDVARS: Eliminated congruent iv.inc: "
<< *IsomorphicInc << '\n');

8
lib/Transforms/Scalar/IndVarSimplify.cpp
View File

@ -846,7 +846,7 @@ protected:
const SCEVAddRecExpr* GetExtendedOperandRecurrence(NarrowIVDefUse DU);
Instruction *WidenIVUse(NarrowIVDefUse DU);
Instruction *WidenIVUse(NarrowIVDefUse DU, SCEVExpander &Rewriter);
void pushNarrowIVUsers(Instruction *NarrowDef, Instruction *WideDef);
};
@ -990,7 +990,7 @@ const SCEVAddRecExpr *WidenIV::GetWideRecurrence(Instruction *NarrowUse) {
/// WidenIVUse - Determine whether an individual user of the narrow IV can be
/// widened. If so, return the wide clone of the user.
Instruction *WidenIV::WidenIVUse(NarrowIVDefUse DU) {
Instruction *WidenIV::WidenIVUse(NarrowIVDefUse DU, SCEVExpander &Rewriter) {
// Stop traversing the def-use chain at inner-loop phis or post-loop phis.
if (isa<PHINode>(DU.NarrowUse) &&
@ -1058,7 +1058,7 @@ Instruction *WidenIV::WidenIVUse(NarrowIVDefUse DU) {
// NarrowUse.
Instruction *WideUse = 0;
if (WideAddRec == WideIncExpr
&& SCEVExpander::hoistStep(WideInc, DU.NarrowUse, DT))
&& Rewriter.hoistIVInc(WideInc, DU.NarrowUse))
WideUse = WideInc;
else {
WideUse = CloneIVUser(DU);
@ -1163,7 +1163,7 @@ PHINode *WidenIV::CreateWideIV(SCEVExpander &Rewriter) {
// Process a def-use edge. This may replace the use, so don't hold a
// use_iterator across it.
Instruction *WideUse = WidenIVUse(DU);
Instruction *WideUse = WidenIVUse(DU, Rewriter);
// Follow all def-use edges from the previous narrow use.
if (WideUse)

26
lib/Transforms/Scalar/LoopStrengthReduce.cpp
View File

@ -1573,9 +1573,11 @@ class LSRInstance {
BasicBlock::iterator
HoistInsertPosition(BasicBlock::iterator IP,
const SmallVectorImpl<Instruction *> &Inputs) const;
BasicBlock::iterator AdjustInsertPositionForExpand(BasicBlock::iterator IP,
const LSRFixup &LF,
const LSRUse &LU) const;
BasicBlock::iterator
AdjustInsertPositionForExpand(BasicBlock::iterator IP,
const LSRFixup &LF,
const LSRUse &LU,
SCEVExpander &Rewriter) const;
Value *Expand(const LSRFixup &LF,
const Formula &F,
@ -4131,9 +4133,10 @@ LSRInstance::HoistInsertPosition(BasicBlock::iterator IP,
/// AdjustInsertPositionForExpand - Determine an input position which will be
/// dominated by the operands and which will dominate the result.
BasicBlock::iterator
LSRInstance::AdjustInsertPositionForExpand(BasicBlock::iterator IP,
LSRInstance::AdjustInsertPositionForExpand(BasicBlock::iterator LowestIP,
const LSRFixup &LF,
const LSRUse &LU) const {
const LSRUse &LU,
SCEVExpander &Rewriter) const {
// Collect some instructions which must be dominated by the
// expanding replacement. These must be dominated by any operands that
// will be required in the expansion.
@ -4168,9 +4171,13 @@ LSRInstance::AdjustInsertPositionForExpand(BasicBlock::iterator IP,
}
}
assert(!isa<PHINode>(LowestIP) && !isa<LandingPadInst>(LowestIP)
&& !isa<DbgInfoIntrinsic>(LowestIP) &&
"Insertion point must be a normal instruction");
// Then, climb up the immediate dominator tree as far as we can go while
// still being dominated by the input positions.
IP = HoistInsertPosition(IP, Inputs);
BasicBlock::iterator IP = HoistInsertPosition(LowestIP, Inputs);
// Don't insert instructions before PHI nodes.
while (isa<PHINode>(IP)) ++IP;
@ -4181,6 +4188,11 @@ LSRInstance::AdjustInsertPositionForExpand(BasicBlock::iterator IP,
// Ignore debug intrinsics.
while (isa<DbgInfoIntrinsic>(IP)) ++IP;
// Set IP below instructions recently inserted by SCEVExpander. This keeps the
// IP consistent across expansions and allows the previously inserted
// instructions to be reused by subsequent expansion.
while (Rewriter.isInsertedInstruction(IP) && IP != LowestIP) ++IP;
return IP;
}
@ -4195,7 +4207,7 @@ Value *LSRInstance::Expand(const LSRFixup &LF,
// Determine an input position which will be dominated by the operands and
// which will dominate the result.
IP = AdjustInsertPositionForExpand(IP, LF, LU);
IP = AdjustInsertPositionForExpand(IP, LF, LU, Rewriter);
// Inform the Rewriter if we have a post-increment use, so that it can
// perform an advantageous expansion.

37
test/Transforms/LoopStrengthReduce/X86/2012-01-13-phielim.ll
View File

@ -48,3 +48,40 @@ cond.false35.i: ; preds = %for.end.i
exit: ; preds = %cond.true29.i, %cond.true.i
ret i32 0
}
%struct.anon.7.91.199.307.415.475.559.643.751.835.943.1003.1111.1219.1351.1375.1399.1435.1471.1483.1519.1531.1651.1771 = type { i32, i32, i32 }
@tags = external global [5000 x %struct.anon.7.91.199.307.415.475.559.643.751.835.943.1003.1111.1219.1351.1375.1399.1435.1471.1483.1519.1531.1651.1771], align 16
; CHECK: @test2
; CHECK: %entry
; CHECK-NOT: mov
; CHECK: jne
define void @test2(i32 %n) nounwind uwtable {
entry:
br i1 undef, label %while.end, label %for.cond468
for.cond468: ; preds = %if.then477, %entry
%indvars.iv1163 = phi i64 [ %indvars.iv.next1164, %if.then477 ], [ 1, %entry ]
%k.0.in = phi i32* [ %last, %if.then477 ], [ getelementptr inbounds ([5000 x %struct.anon.7.91.199.307.415.475.559.643.751.835.943.1003.1111.1219.1351.1375.1399.1435.1471.1483.1519.1531.1651.1771]* @tags, i64 0, i64 0, i32 2), %entry ]
%k.0 = load i32* %k.0.in, align 4
%0 = trunc i64 %indvars.iv1163 to i32
%cmp469 = icmp slt i32 %0, %n
br i1 %cmp469, label %for.body471, label %for.inc498
for.body471: ; preds = %for.cond468
%first = getelementptr inbounds [5000 x %struct.anon.7.91.199.307.415.475.559.643.751.835.943.1003.1111.1219.1351.1375.1399.1435.1471.1483.1519.1531.1651.1771]* @tags, i64 0, i64 %indvars.iv1163, i32 1
%1 = load i32* %first, align 4
br i1 undef, label %if.then477, label %for.inc498
if.then477: ; preds = %for.body471
%last = getelementptr inbounds [5000 x %struct.anon.7.91.199.307.415.475.559.643.751.835.943.1003.1111.1219.1351.1375.1399.1435.1471.1483.1519.1531.1651.1771]* @tags, i64 0, i64 %indvars.iv1163, i32 2
%indvars.iv.next1164 = add i64 %indvars.iv1163, 1
br label %for.cond468
for.inc498: ; preds = %for.inc498, %for.body471, %for.cond468
br label %for.inc498
while.end: ; preds = %entry
ret void
}