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LSR should only reuse phis that match its formula. 

Fixes rdar://problem/5064068

llvm-svn: 141442
This commit is contained in:
Andrew Trick 2011-10-07 23:46:21 +00:00
parent 195464184e
commit 7fb669ab48
3 changed files with 129 additions and 65 deletions
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19
llvm/include/llvm/Analysis/ScalarEvolutionExpander.h
View File

@ -64,6 +64,11 @@ namespace llvm {
/// in a more literal form.
bool CanonicalMode;
/// When invoked from LSR, the expander is in "strength reduction" mode. The
/// only difference is that phi's are only reused if they are already in
/// "expanded" form.
bool LSRMode;
typedef IRBuilder<true, TargetFolder> BuilderType;
BuilderType Builder;
@ -73,7 +78,8 @@ namespace llvm {
/// SCEVExpander - Construct a SCEVExpander in "canonical" mode.
explicit SCEVExpander(ScalarEvolution &se, const char *name)
: SE(se), IVName(name), IVIncInsertLoop(0), IVIncInsertPos(0),
CanonicalMode(true), Builder(se.getContext(), TargetFolder(se.TD)) {}
CanonicalMode(true), LSRMode(false),
Builder(se.getContext(), TargetFolder(se.TD)) {}
/// clear - Erase the contents of the InsertedExpressions map so that users
/// trying to expand the same expression into multiple BasicBlocks or
@ -88,8 +94,7 @@ namespace llvm {
/// canonical induction variable of the specified type for the specified
/// loop (inserting one if there is none). A canonical induction variable
/// starts at zero and steps by one on each iteration.
PHINode *getOrInsertCanonicalInductionVariable(const Loop *L,
Type *Ty);
PHINode *getOrInsertCanonicalInductionVariable(const Loop *L, Type *Ty);
/// expandCodeFor - Insert code to directly compute the specified SCEV
/// expression into the program. The inserted code is inserted into the
@ -127,13 +132,14 @@ namespace llvm {
/// is useful for late optimization passes.
void disableCanonicalMode() { CanonicalMode = false; }
void enableLSRMode() { LSRMode = true; }
/// clearInsertPoint - Clear the current insertion point. This is useful
/// if the instruction that had been serving as the insertion point may
/// have been deleted.
void clearInsertPoint() {
Builder.ClearInsertionPoint();
}
private:
LLVMContext &getContext() const { return SE.getContext(); }
@ -208,6 +214,11 @@ namespace llvm {
void restoreInsertPoint(BasicBlock *BB, BasicBlock::iterator I);
bool isNormalAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L);
bool isExpandedAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L,
Type *ExpandTy);
Value *expandAddRecExprLiterally(const SCEVAddRecExpr *);
PHINode *getAddRecExprPHILiterally(const SCEVAddRecExpr *Normalized,
const Loop *L,

174
llvm/lib/Analysis/ScalarEvolutionExpander.cpp
View File

@ -17,6 +17,7 @@
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/LLVMContext.h"
#include "llvm/Support/Debug.h"
#include "llvm/Target/TargetData.h"
#include "llvm/ADT/STLExtras.h"
@ -843,6 +844,82 @@ static void ExposePointerBase(const SCEV *&Base, const SCEV *&Rest,
}
}
/// Determine if this is a well-behaved chain of instructions leading back to
/// the PHI. If so, it may be reused by expanded expressions.
bool SCEVExpander::isNormalAddRecExprPHI(PHINode *PN, Instruction *IncV,
const Loop *L) {
if (IncV->getNumOperands() == 0 || isa<PHINode>(IncV) ||
(isa<CastInst>(IncV) && !isa<BitCastInst>(IncV)))
return false;
// If any of the operands don't dominate the insert position, bail.
// Addrec operands are always loop-invariant, so this can only happen
// if there are instructions which haven't been hoisted.
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;
}
// Advance to the next instruction.
IncV = dyn_cast<Instruction>(IncV->getOperand(0));
if (!IncV)
return false;
if (IncV->mayHaveSideEffects())
return false;
if (IncV != PN)
return true;
return isNormalAddRecExprPHI(PN, IncV, L);
}
/// 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
/// should match any patterns generated by getAddRecExprPHILiterally and
/// expandAddtoGEP.
bool SCEVExpander::isExpandedAddRecExprPHI(PHINode *PN, Instruction *IncV,
const Loop *L, Type *ExpandTy) {
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>(ExpandTy)->getAddressSpace();
if (IncV->getType() != Type::getInt1PtrTy(SE.getContext(), AS)
&& IncV->getType() != Type::getInt8PtrTy(SE.getContext(), AS))
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;
}
}
/// getAddRecExprPHILiterally - Helper for expandAddRecExprLiterally. Expand
/// the base addrec, which is the addrec without any non-loop-dominating
/// values, and return the PHI.
@ -854,70 +931,45 @@ SCEVExpander::getAddRecExprPHILiterally(const SCEVAddRecExpr *Normalized,
assert((!IVIncInsertLoop||IVIncInsertPos) && "Uninitialized insert position");
// Reuse a previously-inserted PHI, if present.
for (BasicBlock::iterator I = L->getHeader()->begin();
PHINode *PN = dyn_cast<PHINode>(I); ++I)
if (SE.isSCEVable(PN->getType()) &&
(SE.getEffectiveSCEVType(PN->getType()) ==
SE.getEffectiveSCEVType(Normalized->getType())) &&
SE.getSCEV(PN) == Normalized)
if (BasicBlock *LatchBlock = L->getLoopLatch()) {
Instruction *IncV =
cast<Instruction>(PN->getIncomingValueForBlock(LatchBlock));
BasicBlock *LatchBlock = L->getLoopLatch();
if (LatchBlock) {
for (BasicBlock::iterator I = L->getHeader()->begin();
PHINode *PN = dyn_cast<PHINode>(I); ++I) {
if (!SE.isSCEVable(PN->getType()) ||
(SE.getEffectiveSCEVType(PN->getType()) !=
SE.getEffectiveSCEVType(Normalized->getType())) ||
SE.getSCEV(PN) != Normalized)
continue;
// Determine if this is a well-behaved chain of instructions leading
// back to the PHI. It probably will be, if we're scanning an inner
// loop already visited by LSR for example, but it wouldn't have
// to be.
do {
if (IncV->getNumOperands() == 0 || isa<PHINode>(IncV) ||
(isa<CastInst>(IncV) && !isa<BitCastInst>(IncV))) {
IncV = 0;
break;
}
// If any of the operands don't dominate the insert position, bail.
// Addrec operands are always loop-invariant, so this can only happen
// if there are instructions which haven't been hoisted.
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)) {
IncV = 0;
break;
}
}
if (!IncV)
break;
// Advance to the next instruction.
IncV = dyn_cast<Instruction>(IncV->getOperand(0));
if (!IncV)
break;
if (IncV->mayHaveSideEffects()) {
IncV = 0;
break;
}
} while (IncV != PN);
Instruction *IncV =
cast<Instruction>(PN->getIncomingValueForBlock(LatchBlock));
if (IncV) {
// Ok, the add recurrence looks usable.
// Remember this PHI, even in post-inc mode.
InsertedValues.insert(PN);
// Remember the increment.
IncV = cast<Instruction>(PN->getIncomingValueForBlock(LatchBlock));
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;
}
if (LSRMode) {
if (!isExpandedAddRecExprPHI(PN, IncV, L, ExpandTy))
continue;
}
else {
if (!isNormalAddRecExprPHI(PN, IncV, L))
continue;
}
// 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;
}
}
// Save the original insertion point so we can restore it when we're done.
BasicBlock *SaveInsertBB = Builder.GetInsertBlock();

1
llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
View File

@ -3770,6 +3770,7 @@ LSRInstance::ImplementSolution(const SmallVectorImpl<const Formula *> &Solution,
SCEVExpander Rewriter(SE, "lsr");
Rewriter.disableCanonicalMode();
Rewriter.enableLSRMode();
Rewriter.setIVIncInsertPos(L, IVIncInsertPos);
// Expand the new value definitions and update the users.