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Fix two significant bugs in LSR:

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1. When rewriting code in outer loops, sometimes we would insert code into
   inner loops that is invariant in that loop.
2. Notice that 4*(2+x) is 8+4*x and use that to simplify expressions.

This is a performance neutral change.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@25964 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2006-02-04 07:36:50 +00:00
parent a6973c348b
commit 221fc3c6d6
1 changed files with 75 additions and 14 deletions
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89
lib/Transforms/Scalar/LoopStrengthReduce.cpp
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@ -477,6 +477,10 @@ namespace {
void RewriteInstructionToUseNewBase(const SCEVHandle &NewBase,
SCEVExpander &Rewriter, Loop *L,
Pass *P);
Value *InsertCodeForBaseAtPosition(const SCEVHandle &NewBase,
SCEVExpander &Rewriter,
Instruction *IP, Loop *L);
void dump() const;
};
}
@ -490,6 +494,41 @@ void BasedUser::dump() const {
std::cerr << " Inst: " << *Inst;
}
Value *BasedUser::InsertCodeForBaseAtPosition(const SCEVHandle &NewBase,
SCEVExpander &Rewriter,
Instruction *IP, Loop *L) {
// Figure out where we *really* want to insert this code. In particular, if
// the user is inside of a loop that is nested inside of L, we really don't
// want to insert this expression before the user, we'd rather pull it out as
// many loops as possible.
LoopInfo &LI = Rewriter.getLoopInfo();
Instruction *BaseInsertPt = IP;
// Figure out the most-nested loop that IP is in.
Loop *InsertLoop = LI.getLoopFor(IP->getParent());
// If InsertLoop is not L, and InsertLoop is nested inside of L, figure out
// the preheader of the outer-most loop where NewBase is not loop invariant.
while (InsertLoop && NewBase->isLoopInvariant(InsertLoop)) {
BaseInsertPt = InsertLoop->getLoopPreheader()->getTerminator();
InsertLoop = InsertLoop->getParentLoop();
}
// If there is no immediate value, skip the next part.
if (SCEVConstant *SC = dyn_cast<SCEVConstant>(Imm))
if (SC->getValue()->isNullValue())
return Rewriter.expandCodeFor(NewBase, BaseInsertPt,
OperandValToReplace->getType());
Value *Base = Rewriter.expandCodeFor(NewBase, BaseInsertPt);
// Always emit the immediate (if non-zero) into the same block as the user.
SCEVHandle NewValSCEV = SCEVAddExpr::get(SCEVUnknown::get(Base), Imm);
return Rewriter.expandCodeFor(NewValSCEV, IP,
OperandValToReplace->getType());
}
// Once we rewrite the code to insert the new IVs we want, update the
// operands of Inst to use the new expression 'NewBase', with 'Imm' added
// to it.
@ -497,9 +536,7 @@ void BasedUser::RewriteInstructionToUseNewBase(const SCEVHandle &NewBase,
SCEVExpander &Rewriter,
Loop *L, Pass *P) {
if (!isa<PHINode>(Inst)) {
SCEVHandle NewValSCEV = SCEVAddExpr::get(NewBase, Imm);
Value *NewVal = Rewriter.expandCodeFor(NewValSCEV, Inst,
OperandValToReplace->getType());
Value *NewVal = InsertCodeForBaseAtPosition(NewBase, Rewriter, Inst, L);
// Replace the use of the operand Value with the new Phi we just created.
Inst->replaceUsesOfWith(OperandValToReplace, NewVal);
DEBUG(std::cerr << " CHANGED: IMM =" << *Imm << " Inst = " << *Inst);
@ -539,11 +576,8 @@ void BasedUser::RewriteInstructionToUseNewBase(const SCEVHandle &NewBase,
Value *&Code = InsertedCode[PN->getIncomingBlock(i)];
if (!Code) {
// Insert the code into the end of the predecessor block.
BasicBlock::iterator InsertPt =PN->getIncomingBlock(i)->getTerminator();
SCEVHandle NewValSCEV = SCEVAddExpr::get(NewBase, Imm);
Code = Rewriter.expandCodeFor(NewValSCEV, InsertPt,
OperandValToReplace->getType());
Instruction *InsertPt = PN->getIncomingBlock(i)->getTerminator();
Code = InsertCodeForBaseAtPosition(NewBase, Rewriter, InsertPt, L);
}
// Replace the use of the operand Value with the new Phi we just created.
@ -627,16 +661,18 @@ static void MoveImmediateValues(SCEVHandle &Val, SCEVHandle &Imm,
std::vector<SCEVHandle> NewOps;
NewOps.reserve(SAE->getNumOperands());
for (unsigned i = 0; i != SAE->getNumOperands(); ++i)
if (isAddress && isTargetConstant(SAE->getOperand(i))) {
Imm = SCEVAddExpr::get(Imm, SAE->getOperand(i));
} else if (!SAE->getOperand(i)->isLoopInvariant(L)) {
for (unsigned i = 0; i != SAE->getNumOperands(); ++i) {
SCEVHandle NewOp = SAE->getOperand(i);
MoveImmediateValues(NewOp, Imm, isAddress, L);
if (!NewOp->isLoopInvariant(L)) {
// If this is a loop-variant expression, it must stay in the immediate
// field of the expression.
Imm = SCEVAddExpr::get(Imm, SAE->getOperand(i));
Imm = SCEVAddExpr::get(Imm, NewOp);
} else {
NewOps.push_back(SAE->getOperand(i));
NewOps.push_back(NewOp);
}
}
if (NewOps.empty())
Val = SCEVUnknown::getIntegerSCEV(0, Val->getType());
@ -654,6 +690,31 @@ static void MoveImmediateValues(SCEVHandle &Val, SCEVHandle &Imm,
Val = SCEVAddRecExpr::get(Ops, SARE->getLoop());
}
return;
} else if (SCEVMulExpr *SME = dyn_cast<SCEVMulExpr>(Val)) {
// Transform "8 * (4 + v)" -> "32 + 8*V" if "32" fits in the immed field.
if (isAddress && isTargetConstant(SME->getOperand(0)) &&
SME->getNumOperands() == 2 && SME->isLoopInvariant(L)) {
SCEVHandle SubImm = SCEVUnknown::getIntegerSCEV(0, Val->getType());
SCEVHandle NewOp = SME->getOperand(1);
MoveImmediateValues(NewOp, SubImm, isAddress, L);
// If we extracted something out of the subexpressions, see if we can
// simplify this!
if (NewOp != SME->getOperand(1)) {
// Scale SubImm up by "8". If the result is a target constant, we are
// good.
SubImm = SCEVMulExpr::get(SubImm, SME->getOperand(0));
if (isTargetConstant(SubImm)) {
// Accumulate the immediate.
Imm = SCEVAddExpr::get(Imm, SubImm);
// Update what is left of 'Val'.
Val = SCEVMulExpr::get(SME->getOperand(0), NewOp);
return;
}
}
}
}
// Loop-variant expressions must stay in the immediate field of the