mirror of
https://github.com/RPCSX/llvm.git
synced 2024-12-11 05:35:11 +00:00
7be7739e12
.cpp files are unambiguously C++, you only need the mode markers on .h files. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@267353 91177308-0d34-0410-b5e6-96231b3b80d8
255 lines
10 KiB
C++
255 lines
10 KiB
C++
//===- ScalarEvolutionNormalization.cpp - See below -----------------------===//
|
|
//
|
|
// The LLVM Compiler Infrastructure
|
|
//
|
|
// This file is distributed under the University of Illinois Open Source
|
|
// License. See LICENSE.TXT for details.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
//
|
|
// This file implements utilities for working with "normalized" expressions.
|
|
// See the comments at the top of ScalarEvolutionNormalization.h for details.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#include "llvm/IR/Dominators.h"
|
|
#include "llvm/Analysis/LoopInfo.h"
|
|
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
|
|
#include "llvm/Analysis/ScalarEvolutionNormalization.h"
|
|
using namespace llvm;
|
|
|
|
/// IVUseShouldUsePostIncValue - We have discovered a "User" of an IV expression
|
|
/// and now we need to decide whether the user should use the preinc or post-inc
|
|
/// value. If this user should use the post-inc version of the IV, return true.
|
|
///
|
|
/// Choosing wrong here can break dominance properties (if we choose to use the
|
|
/// post-inc value when we cannot) or it can end up adding extra live-ranges to
|
|
/// the loop, resulting in reg-reg copies (if we use the pre-inc value when we
|
|
/// should use the post-inc value).
|
|
static bool IVUseShouldUsePostIncValue(Instruction *User, Value *Operand,
|
|
const Loop *L, DominatorTree *DT) {
|
|
// If the user is in the loop, use the preinc value.
|
|
if (L->contains(User)) return false;
|
|
|
|
BasicBlock *LatchBlock = L->getLoopLatch();
|
|
if (!LatchBlock)
|
|
return false;
|
|
|
|
// Ok, the user is outside of the loop. If it is dominated by the latch
|
|
// block, use the post-inc value.
|
|
if (DT->dominates(LatchBlock, User->getParent()))
|
|
return true;
|
|
|
|
// There is one case we have to be careful of: PHI nodes. These little guys
|
|
// can live in blocks that are not dominated by the latch block, but (since
|
|
// their uses occur in the predecessor block, not the block the PHI lives in)
|
|
// should still use the post-inc value. Check for this case now.
|
|
PHINode *PN = dyn_cast<PHINode>(User);
|
|
if (!PN || !Operand) return false; // not a phi, not dominated by latch block.
|
|
|
|
// Look at all of the uses of Operand by the PHI node. If any use corresponds
|
|
// to a block that is not dominated by the latch block, give up and use the
|
|
// preincremented value.
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
|
|
if (PN->getIncomingValue(i) == Operand &&
|
|
!DT->dominates(LatchBlock, PN->getIncomingBlock(i)))
|
|
return false;
|
|
|
|
// Okay, all uses of Operand by PN are in predecessor blocks that really are
|
|
// dominated by the latch block. Use the post-incremented value.
|
|
return true;
|
|
}
|
|
|
|
namespace {
|
|
|
|
/// Hold the state used during post-inc expression transformation, including a
|
|
/// map of transformed expressions.
|
|
class PostIncTransform {
|
|
TransformKind Kind;
|
|
PostIncLoopSet &Loops;
|
|
ScalarEvolution &SE;
|
|
DominatorTree &DT;
|
|
|
|
DenseMap<const SCEV*, const SCEV*> Transformed;
|
|
|
|
public:
|
|
PostIncTransform(TransformKind kind, PostIncLoopSet &loops,
|
|
ScalarEvolution &se, DominatorTree &dt):
|
|
Kind(kind), Loops(loops), SE(se), DT(dt) {}
|
|
|
|
const SCEV *TransformSubExpr(const SCEV *S, Instruction *User,
|
|
Value *OperandValToReplace);
|
|
|
|
protected:
|
|
const SCEV *TransformImpl(const SCEV *S, Instruction *User,
|
|
Value *OperandValToReplace);
|
|
};
|
|
|
|
} // namespace
|
|
|
|
/// Implement post-inc transformation for all valid expression types.
|
|
const SCEV *PostIncTransform::
|
|
TransformImpl(const SCEV *S, Instruction *User, Value *OperandValToReplace) {
|
|
|
|
if (const SCEVCastExpr *X = dyn_cast<SCEVCastExpr>(S)) {
|
|
const SCEV *O = X->getOperand();
|
|
const SCEV *N = TransformSubExpr(O, User, OperandValToReplace);
|
|
if (O != N)
|
|
switch (S->getSCEVType()) {
|
|
case scZeroExtend: return SE.getZeroExtendExpr(N, S->getType());
|
|
case scSignExtend: return SE.getSignExtendExpr(N, S->getType());
|
|
case scTruncate: return SE.getTruncateExpr(N, S->getType());
|
|
default: llvm_unreachable("Unexpected SCEVCastExpr kind!");
|
|
}
|
|
return S;
|
|
}
|
|
|
|
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
|
|
// An addrec. This is the interesting part.
|
|
SmallVector<const SCEV *, 8> Operands;
|
|
const Loop *L = AR->getLoop();
|
|
// The addrec conceptually uses its operands at loop entry.
|
|
Instruction *LUser = &L->getHeader()->front();
|
|
// Transform each operand.
|
|
for (SCEVNAryExpr::op_iterator I = AR->op_begin(), E = AR->op_end();
|
|
I != E; ++I) {
|
|
Operands.push_back(TransformSubExpr(*I, LUser, nullptr));
|
|
}
|
|
// Conservatively use AnyWrap until/unless we need FlagNW.
|
|
const SCEV *Result = SE.getAddRecExpr(Operands, L, SCEV::FlagAnyWrap);
|
|
switch (Kind) {
|
|
case NormalizeAutodetect:
|
|
// Normalize this SCEV by subtracting the expression for the final step.
|
|
// We only allow affine AddRecs to be normalized, otherwise we would not
|
|
// be able to correctly denormalize.
|
|
// e.g. {1,+,3,+,2} == {-2,+,1,+,2} + {3,+,2}
|
|
// Normalized form: {-2,+,1,+,2}
|
|
// Denormalized form: {1,+,3,+,2}
|
|
//
|
|
// However, denormalization would use a different step expression than
|
|
// normalization (see getPostIncExpr), generating the wrong final
|
|
// expression: {-2,+,1,+,2} + {1,+,2} => {-1,+,3,+,2}
|
|
if (AR->isAffine() &&
|
|
IVUseShouldUsePostIncValue(User, OperandValToReplace, L, &DT)) {
|
|
const SCEV *TransformedStep =
|
|
TransformSubExpr(AR->getStepRecurrence(SE),
|
|
User, OperandValToReplace);
|
|
Result = SE.getMinusSCEV(Result, TransformedStep);
|
|
Loops.insert(L);
|
|
}
|
|
#if 0
|
|
// This assert is conceptually correct, but ScalarEvolution currently
|
|
// sometimes fails to canonicalize two equal SCEVs to exactly the same
|
|
// form. It's possibly a pessimization when this happens, but it isn't a
|
|
// correctness problem, so disable this assert for now.
|
|
assert(S == TransformSubExpr(Result, User, OperandValToReplace) &&
|
|
"SCEV normalization is not invertible!");
|
|
#endif
|
|
break;
|
|
case Normalize:
|
|
// We want to normalize step expression, because otherwise we might not be
|
|
// able to denormalize to the original expression.
|
|
//
|
|
// Here is an example what will happen if we don't normalize step:
|
|
// ORIGINAL ISE:
|
|
// {(100 /u {1,+,1}<%bb16>),+,(100 /u {1,+,1}<%bb16>)}<%bb25>
|
|
// NORMALIZED ISE:
|
|
// {((-1 * (100 /u {1,+,1}<%bb16>)) + (100 /u {0,+,1}<%bb16>)),+,
|
|
// (100 /u {0,+,1}<%bb16>)}<%bb25>
|
|
// DENORMALIZED BACK ISE:
|
|
// {((2 * (100 /u {1,+,1}<%bb16>)) + (-1 * (100 /u {2,+,1}<%bb16>))),+,
|
|
// (100 /u {1,+,1}<%bb16>)}<%bb25>
|
|
// Note that the initial value changes after normalization +
|
|
// denormalization, which isn't correct.
|
|
if (Loops.count(L)) {
|
|
const SCEV *TransformedStep =
|
|
TransformSubExpr(AR->getStepRecurrence(SE),
|
|
User, OperandValToReplace);
|
|
Result = SE.getMinusSCEV(Result, TransformedStep);
|
|
}
|
|
#if 0
|
|
// See the comment on the assert above.
|
|
assert(S == TransformSubExpr(Result, User, OperandValToReplace) &&
|
|
"SCEV normalization is not invertible!");
|
|
#endif
|
|
break;
|
|
case Denormalize:
|
|
// Here we want to normalize step expressions for the same reasons, as
|
|
// stated above.
|
|
if (Loops.count(L)) {
|
|
const SCEV *TransformedStep =
|
|
TransformSubExpr(AR->getStepRecurrence(SE),
|
|
User, OperandValToReplace);
|
|
Result = SE.getAddExpr(Result, TransformedStep);
|
|
}
|
|
break;
|
|
}
|
|
return Result;
|
|
}
|
|
|
|
if (const SCEVNAryExpr *X = dyn_cast<SCEVNAryExpr>(S)) {
|
|
SmallVector<const SCEV *, 8> Operands;
|
|
bool Changed = false;
|
|
// Transform each operand.
|
|
for (SCEVNAryExpr::op_iterator I = X->op_begin(), E = X->op_end();
|
|
I != E; ++I) {
|
|
const SCEV *O = *I;
|
|
const SCEV *N = TransformSubExpr(O, User, OperandValToReplace);
|
|
Changed |= N != O;
|
|
Operands.push_back(N);
|
|
}
|
|
// If any operand actually changed, return a transformed result.
|
|
if (Changed)
|
|
switch (S->getSCEVType()) {
|
|
case scAddExpr: return SE.getAddExpr(Operands);
|
|
case scMulExpr: return SE.getMulExpr(Operands);
|
|
case scSMaxExpr: return SE.getSMaxExpr(Operands);
|
|
case scUMaxExpr: return SE.getUMaxExpr(Operands);
|
|
default: llvm_unreachable("Unexpected SCEVNAryExpr kind!");
|
|
}
|
|
return S;
|
|
}
|
|
|
|
if (const SCEVUDivExpr *X = dyn_cast<SCEVUDivExpr>(S)) {
|
|
const SCEV *LO = X->getLHS();
|
|
const SCEV *RO = X->getRHS();
|
|
const SCEV *LN = TransformSubExpr(LO, User, OperandValToReplace);
|
|
const SCEV *RN = TransformSubExpr(RO, User, OperandValToReplace);
|
|
if (LO != LN || RO != RN)
|
|
return SE.getUDivExpr(LN, RN);
|
|
return S;
|
|
}
|
|
|
|
llvm_unreachable("Unexpected SCEV kind!");
|
|
}
|
|
|
|
/// Manage recursive transformation across an expression DAG. Revisiting
|
|
/// expressions would lead to exponential recursion.
|
|
const SCEV *PostIncTransform::
|
|
TransformSubExpr(const SCEV *S, Instruction *User, Value *OperandValToReplace) {
|
|
|
|
if (isa<SCEVConstant>(S) || isa<SCEVUnknown>(S))
|
|
return S;
|
|
|
|
const SCEV *Result = Transformed.lookup(S);
|
|
if (Result)
|
|
return Result;
|
|
|
|
Result = TransformImpl(S, User, OperandValToReplace);
|
|
Transformed[S] = Result;
|
|
return Result;
|
|
}
|
|
|
|
/// Top level driver for transforming an expression DAG into its requested
|
|
/// post-inc form (either "Normalized" or "Denormalized").
|
|
const SCEV *llvm::TransformForPostIncUse(TransformKind Kind,
|
|
const SCEV *S,
|
|
Instruction *User,
|
|
Value *OperandValToReplace,
|
|
PostIncLoopSet &Loops,
|
|
ScalarEvolution &SE,
|
|
DominatorTree &DT) {
|
|
PostIncTransform Transform(Kind, Loops, SE, DT);
|
|
return Transform.TransformSubExpr(S, User, OperandValToReplace);
|
|
}
|