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Rename ScalarEvolution's getIterationCount to getBackedgeTakenCount,

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to more accurately describe what it does. Expand its doxygen comment
to describe what the backedge-taken count is and how it differs
from the actual iteration count of the loop. Adjust names and
comments in associated code accordingly.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@65382 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman
2009-02-24 18:55:53 +00:00
parent 57f0db833d
commit 46bdfb0e6b
21 changed files with 177 additions and 145 deletions
Download Patch File Download Diff File Expand all files Collapse all files

71
lib/Transforms/Scalar/IndVarSimplify.cpp
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@@ -93,12 +93,12 @@ namespace {
void EliminatePointerRecurrence(PHINode *PN, BasicBlock *Preheader,
SmallPtrSet<Instruction*, 16> &DeadInsts);
void LinearFunctionTestReplace(Loop *L, SCEVHandle IterationCount,
void LinearFunctionTestReplace(Loop *L, SCEVHandle BackedgeTakenCount,
Value *IndVar,
BasicBlock *ExitingBlock,
BranchInst *BI,
SCEVExpander &Rewriter);
void RewriteLoopExitValues(Loop *L, SCEV *IterationCount);
void RewriteLoopExitValues(Loop *L, SCEV *BackedgeTakenCount);
void DeleteTriviallyDeadInstructions(SmallPtrSet<Instruction*, 16> &Insts);
@@ -232,7 +232,7 @@ void IndVarSimplify::EliminatePointerRecurrence(PHINode *PN,
/// SCEV analysis can determine a loop-invariant trip count of the loop, which
/// is actually a much broader range than just linear tests.
void IndVarSimplify::LinearFunctionTestReplace(Loop *L,
SCEVHandle IterationCount,
SCEVHandle BackedgeTakenCount,
Value *IndVar,
BasicBlock *ExitingBlock,
BranchInst *BI,
@@ -241,43 +241,41 @@ void IndVarSimplify::LinearFunctionTestReplace(Loop *L,
// against the preincremented value, otherwise we prefer to compare against
// the post-incremented value.
Value *CmpIndVar;
SCEVHandle RHS = BackedgeTakenCount;
if (ExitingBlock == L->getLoopLatch()) {
// What ScalarEvolution calls the "iteration count" is actually the
// number of times the branch is taken. Add one to get the number
// of times the branch is executed. If this addition may overflow,
// we have to be more pessimistic and cast the induction variable
// before doing the add.
SCEVHandle Zero = SE->getIntegerSCEV(0, IterationCount->getType());
// Add one to the "backedge-taken" count to get the trip count.
// If this addition may overflow, we have to be more pessimistic and
// cast the induction variable before doing the add.
SCEVHandle Zero = SE->getIntegerSCEV(0, BackedgeTakenCount->getType());
SCEVHandle N =
SE->getAddExpr(IterationCount,
SE->getIntegerSCEV(1, IterationCount->getType()));
SE->getAddExpr(BackedgeTakenCount,
SE->getIntegerSCEV(1, BackedgeTakenCount->getType()));
if ((isa<SCEVConstant>(N) && !N->isZero()) ||
SE->isLoopGuardedByCond(L, ICmpInst::ICMP_NE, N, Zero)) {
// No overflow. Cast the sum.
IterationCount = SE->getTruncateOrZeroExtend(N, IndVar->getType());
RHS = SE->getTruncateOrZeroExtend(N, IndVar->getType());
} else {
// Potential overflow. Cast before doing the add.
IterationCount = SE->getTruncateOrZeroExtend(IterationCount,
IndVar->getType());
IterationCount =
SE->getAddExpr(IterationCount,
SE->getIntegerSCEV(1, IndVar->getType()));
RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount,
IndVar->getType());
RHS = SE->getAddExpr(RHS,
SE->getIntegerSCEV(1, IndVar->getType()));
}
// The IterationCount expression contains the number of times that the
// backedge actually branches to the loop header. This is one less than the
// number of times the loop executes, so add one to it.
// The BackedgeTaken expression contains the number of times that the
// backedge branches to the loop header. This is one less than the
// number of times the loop executes, so use the incremented indvar.
CmpIndVar = L->getCanonicalInductionVariableIncrement();
} else {
// We have to use the preincremented value...
IterationCount = SE->getTruncateOrZeroExtend(IterationCount,
IndVar->getType());
RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount,
IndVar->getType());
CmpIndVar = IndVar;
}
// Expand the code for the iteration count into the preheader of the loop.
BasicBlock *Preheader = L->getLoopPreheader();
Value *ExitCnt = Rewriter.expandCodeFor(IterationCount,
Value *ExitCnt = Rewriter.expandCodeFor(RHS,
Preheader->getTerminator());
// Insert a new icmp_ne or icmp_eq instruction before the branch.
@@ -291,7 +289,7 @@ void IndVarSimplify::LinearFunctionTestReplace(Loop *L,
<< " LHS:" << *CmpIndVar // includes a newline
<< " op:\t"
<< (Opcode == ICmpInst::ICMP_NE ? "!=" : "==") << "\n"
<< " RHS:\t" << *IterationCount << "\n";
<< " RHS:\t" << *RHS << "\n";
Value *Cond = new ICmpInst(Opcode, CmpIndVar, ExitCnt, "exitcond", BI);
BI->setCondition(Cond);
@@ -304,7 +302,7 @@ void IndVarSimplify::LinearFunctionTestReplace(Loop *L,
/// final value of any expressions that are recurrent in the loop, and
/// substitute the exit values from the loop into any instructions outside of
/// the loop that use the final values of the current expressions.
void IndVarSimplify::RewriteLoopExitValues(Loop *L, SCEV *IterationCount) {
void IndVarSimplify::RewriteLoopExitValues(Loop *L, SCEV *BackedgeTakenCount) {
BasicBlock *Preheader = L->getLoopPreheader();
// Scan all of the instructions in the loop, looking at those that have
@@ -322,7 +320,7 @@ void IndVarSimplify::RewriteLoopExitValues(Loop *L, SCEV *IterationCount) {
BlockToInsertInto = Preheader;
BasicBlock::iterator InsertPt = BlockToInsertInto->getFirstNonPHI();
bool HasConstantItCount = isa<SCEVConstant>(IterationCount);
bool HasConstantItCount = isa<SCEVConstant>(BackedgeTakenCount);
SmallPtrSet<Instruction*, 16> InstructionsToDelete;
std::map<Instruction*, Value*> ExitValues;
@@ -435,7 +433,7 @@ void IndVarSimplify::RewriteNonIntegerIVs(Loop *L) {
// may not have been able to compute a trip count. Now that we've done some
// re-writing, the trip count may be computable.
if (Changed)
SE->forgetLoopIterationCount(L);
SE->forgetLoopBackedgeTakenCount(L);
if (!DeadInsts.empty())
DeleteTriviallyDeadInstructions(DeadInsts);
@@ -473,7 +471,8 @@ static const Type *getEffectiveIndvarType(const PHINode *Phi) {
/// variables, return the PHI for this induction variable.
///
/// TODO: This duplicates a fair amount of ScalarEvolution logic.
/// Perhaps this can be merged with ScalarEvolution::getIterationCount
/// Perhaps this can be merged with
/// ScalarEvolution::getBackedgeTakenCount
/// and/or ScalarEvolution::get{Sign,Zero}ExtendExpr.
///
static const PHINode *TestOrigIVForWrap(const Loop *L,
@@ -622,9 +621,9 @@ bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
// loop into any instructions outside of the loop that use the final values of
// the current expressions.
//
SCEVHandle IterationCount = SE->getIterationCount(L);
if (!isa<SCEVCouldNotCompute>(IterationCount))
RewriteLoopExitValues(L, IterationCount);
SCEVHandle BackedgeTakenCount = SE->getBackedgeTakenCount(L);
if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount))
RewriteLoopExitValues(L, BackedgeTakenCount);
// Next, analyze all of the induction variables in the loop, canonicalizing
// auxillary induction variables.
@@ -649,9 +648,9 @@ bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
// the set of the types of the other recurrence expressions.
const Type *LargestType = 0;
SmallSetVector<const Type *, 4> SizesToInsert;
if (!isa<SCEVCouldNotCompute>(IterationCount)) {
LargestType = IterationCount->getType();
SizesToInsert.insert(IterationCount->getType());
if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount)) {
LargestType = BackedgeTakenCount->getType();
SizesToInsert.insert(BackedgeTakenCount->getType());
}
for (unsigned i = 0, e = IndVars.size(); i != e; ++i) {
const PHINode *PN = IndVars[i].first;
@@ -682,7 +681,7 @@ bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
bool NoSignedWrap = false;
bool NoUnsignedWrap = false;
const PHINode *OrigControllingPHI = 0;
if (!isa<SCEVCouldNotCompute>(IterationCount) && ExitingBlock)
if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount) && ExitingBlock)
// Can't rewrite non-branch yet.
if (BranchInst *BI = dyn_cast<BranchInst>(ExitingBlock->getTerminator())) {
if (Instruction *OrigCond = dyn_cast<Instruction>(BI->getCondition())) {
@@ -695,7 +694,7 @@ bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
DeadInsts.insert(OrigCond);
}
LinearFunctionTestReplace(L, IterationCount, IndVar,
LinearFunctionTestReplace(L, BackedgeTakenCount, IndVar,
ExitingBlock, BI, Rewriter);
}