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Add some comments, simplify some code, and fix a bug that caused rewriting

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to rewrite with the wrong value.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@26311 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2006-02-22 06:37:14 +00:00
parent 470a6adc78
commit bd28e3f8ef
1 changed files with 26 additions and 34 deletions
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60
lib/Transforms/Scalar/LoopUnswitch.cpp
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@ -88,7 +88,7 @@ namespace {
bool UnswitchIfProfitable(Value *LoopCond, Constant *Val,Loop *L);
unsigned getLoopUnswitchCost(Loop *L, Value *LIC);
void UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val,
bool EntersWhenTrue, BasicBlock *ExitBlock);
BasicBlock *ExitBlock);
void UnswitchNontrivialCondition(Value *LIC, Constant *OnVal, Loop *L);
BasicBlock *SplitEdge(BasicBlock *From, BasicBlock *To);
BasicBlock *SplitBlock(BasicBlock *Old, Instruction *SplitPt);
@ -282,16 +282,17 @@ static BasicBlock *isTrivialLoopExitBlock(Loop *L, BasicBlock *BB) {
/// code duplications (equivalently, it produces a simpler loop and a new empty
/// loop, which gets deleted).
///
/// If this is a trivial condition, return ConstantBool::True if the loop body
/// runs when the condition is true, False if the loop body executes when the
/// condition is false. Otherwise, return null to indicate a complex condition.
static bool IsTrivialUnswitchCondition(Loop *L, Value *Cond,
Constant **Val = 0,
bool *EntersWhenTrue = 0,
/// If this is a trivial condition, return true, otherwise return false. When
/// returning true, this sets Cond and Val to the condition that controls the
/// trivial condition: when Cond dynamically equals Val, the loop is known to
/// exit. Finally, this sets LoopExit to the BB that the loop exits to when
/// Cond == Val.
///
static bool IsTrivialUnswitchCondition(Loop *L, Value *Cond, Constant **Val = 0,
BasicBlock **LoopExit = 0) {
BasicBlock *Header = L->getHeader();
TerminatorInst *HeaderTerm = Header->getTerminator();
BasicBlock *LoopExitBB = 0;
if (BranchInst *BI = dyn_cast<BranchInst>(HeaderTerm)) {
// If the header block doesn't end with a conditional branch on Cond, we
@ -304,9 +305,9 @@ static bool IsTrivialUnswitchCondition(Loop *L, Value *Cond,
// side-effects. If so, determine the value of Cond that causes it to do
// this.
if ((LoopExitBB = isTrivialLoopExitBlock(L, BI->getSuccessor(0)))) {
if (Val) *Val = ConstantBool::False;
} else if ((LoopExitBB = isTrivialLoopExitBlock(L, BI->getSuccessor(1)))) {
if (Val) *Val = ConstantBool::True;
} else if ((LoopExitBB = isTrivialLoopExitBlock(L, BI->getSuccessor(1)))) {
if (Val) *Val = ConstantBool::False;
}
} else if (SwitchInst *SI = dyn_cast<SwitchInst>(HeaderTerm)) {
// If this isn't a switch on Cond, we can't handle it.
@ -320,7 +321,6 @@ static bool IsTrivialUnswitchCondition(Loop *L, Value *Cond,
if ((LoopExitBB = isTrivialLoopExitBlock(L, SI->getSuccessor(i)))) {
// Okay, we found a trivial case, remember the value that is trivial.
if (Val) *Val = SI->getCaseValue(i);
if (EntersWhenTrue) *EntersWhenTrue = false;
break;
}
}
@ -395,11 +395,9 @@ bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val,Loop *L){
// If this is a trivial condition to unswitch (which results in no code
// duplication), do it now.
Constant *CondVal;
bool EntersWhenTrue = true;
BasicBlock *ExitBlock;
if (IsTrivialUnswitchCondition(L, LoopCond, &CondVal,
&EntersWhenTrue, &ExitBlock)) {
UnswitchTrivialCondition(L, LoopCond, CondVal, EntersWhenTrue, ExitBlock);
if (IsTrivialUnswitchCondition(L, LoopCond, &CondVal, &ExitBlock)) {
UnswitchTrivialCondition(L, LoopCond, CondVal, ExitBlock);
} else {
UnswitchNontrivialCondition(LoopCond, Val, L);
}
@ -525,13 +523,12 @@ static void EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val,
/// side-effects), unswitch it. This doesn't involve any code duplication, just
/// moving the conditional branch outside of the loop and updating loop info.
void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond,
Constant *Val, bool EntersWhenTrue,
Constant *Val,
BasicBlock *ExitBlock) {
DEBUG(std::cerr << "loop-unswitch: Trivial-Unswitch loop %"
<< L->getHeader()->getName() << " [" << L->getBlocks().size()
<< " blocks] in Function " << L->getHeader()->getParent()->getName()
<< " on cond: " << *Val << (EntersWhenTrue ? " == " : " != ") <<
*Cond << "\n");
<< " on cond: " << *Val << " == " << *Cond << "\n");
// First step, split the preheader, so that we know that there is a safe place
// to insert the conditional branch. We will change 'OrigPH' to have a
@ -552,12 +549,8 @@ void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond,
// Okay, now we have a position to branch from and a position to branch to,
// insert the new conditional branch.
{
BasicBlock *TrueDest = NewPH, *FalseDest = NewExit;
if (!EntersWhenTrue) std::swap(TrueDest, FalseDest);
EmitPreheaderBranchOnCondition(Cond, Val, TrueDest, FalseDest,
OrigPH->getTerminator());
}
EmitPreheaderBranchOnCondition(Cond, Val, NewExit, NewPH,
OrigPH->getTerminator());
OrigPH->getTerminator()->eraseFromParent();
// We need to reprocess this loop, it could be unswitched again.
@ -566,7 +559,7 @@ void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond,
// Now that we know that the loop is never entered when this condition is a
// particular value, rewrite the loop with this info. We know that this will
// at least eliminate the old branch.
RewriteLoopBodyWithConditionConstant(L, Cond, Val, EntersWhenTrue);
RewriteLoopBodyWithConditionConstant(L, Cond, Val, false);
++NumTrivial;
}
@ -912,11 +905,6 @@ void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
// ...
// if (li1 > li2)
// ...
// NotVal - If Val is a bool, this contains its inverse.
Constant *NotVal = 0;
if (ConstantBool *CB = dyn_cast<ConstantBool>(Val))
NotVal = ConstantBool::get(!CB->getValue());
// FOLD boolean conditions (X|LIC), (X&LIC). Fold conditional branches,
// selects, switches.
@ -925,8 +913,12 @@ void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
// If we know that LIC == Val, or that LIC == NotVal, just replace uses of LIC
// in the loop with the appropriate one directly.
if (IsEqual || NotVal) {
Value *Replacement = NotVal ? NotVal : Val;
if (IsEqual || isa<ConstantBool>(Val)) {
Value *Replacement;
if (IsEqual)
Replacement = Val;
else
Replacement = ConstantBool::get(!cast<ConstantBool>(Val)->getValue());
for (unsigned i = 0, e = Users.size(); i != e; ++i)
if (Instruction *U = cast<Instruction>(Users[i])) {
@ -978,7 +970,6 @@ void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
/// pass.
///
void LoopUnswitch::SimplifyCode(std::vector<Instruction*> &Worklist) {
Worklist.back()->getParent()->getParent()->viewCFG();
while (!Worklist.empty()) {
Instruction *I = Worklist.back();
Worklist.pop_back();
@ -1066,9 +1057,10 @@ void LoopUnswitch::SimplifyCode(std::vector<Instruction*> &Worklist) {
Succ->eraseFromParent();
++NumSimplify;
} else if (ConstantBool *CB = dyn_cast<ConstantBool>(BI->getCondition())){
break; // FIXME: Enable.
// Conditional branch. Turn it into an unconditional branch, then
// remove dead blocks.
break; // FIXME: Enable.
DEBUG(std::cerr << "Folded branch: " << *BI);
BasicBlock *DeadSucc = BI->getSuccessor(CB->getValue());
BasicBlock *LiveSucc = BI->getSuccessor(!CB->getValue());