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Fix bug in updating dominance frontier after loop 

unswitch when frontier includes basic blocks that 
are not inside loop.

llvm-svn: 42654
This commit is contained in:
Devang Patel 2007-10-05 22:29:34 +00:00
parent d3ccf00870
commit a69f987b66
3 changed files with 151 additions and 29 deletions
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144
llvm/lib/Transforms/Scalar/LoopUnswitch.cpp
View File

@ -41,7 +41,6 @@
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
@ -71,6 +70,18 @@ namespace {
bool OptimizeForSize;
bool redoLoop;
DominanceFrontier *DF;
DominatorTree *DT;
/// LoopDF - Loop's dominance frontier. This set is a collection of
/// loop exiting blocks' DF member blocks. However this does set does not
/// includes basic blocks that are inside loop.
SmallPtrSet<BasicBlock *, 8> LoopDF;
/// OrigLoopExitMap - This is used to map loop exiting block with
/// corresponding loop exit block, before updating CFG.
DenseMap<BasicBlock *, BasicBlock *> OrigLoopExitMap;
public:
static char ID; // Pass ID, replacement for typeid
explicit LoopUnswitch(bool Os = false) :
@ -106,8 +117,13 @@ namespace {
/// Split all of the edges from inside the loop to their exit blocks. Update
/// the appropriate Phi nodes as we do so.
void SplitExitEdges(const SmallVector<BasicBlock *, 8> &ExitBlocks,
void SplitExitEdges(Loop *L, const SmallVector<BasicBlock *, 8> &ExitBlocks,
SmallVector<BasicBlock *, 8> &MiddleBlocks);
/// If BB's dominance frontier has a member that is not part of loop L then
/// remove it. Add NewDFMember in BB's dominance frontier.
void ReplaceLoopExternalDFMember(Loop *L, BasicBlock *BB,
BasicBlock *NewDFMember);
bool UnswitchIfProfitable(Value *LoopCond, Constant *Val,Loop *L);
unsigned getLoopUnswitchCost(Loop *L, Value *LIC);
@ -158,13 +174,16 @@ static Value *FindLIVLoopCondition(Value *Cond, Loop *L, bool &Changed) {
if (Value *RHS = FindLIVLoopCondition(BO->getOperand(1), L, Changed))
return RHS;
}
return 0;
return 0;
}
bool LoopUnswitch::runOnLoop(Loop *L, LPPassManager &LPM_Ref) {
LI = &getAnalysis<LoopInfo>();
LPM = &LPM_Ref;
DF = getAnalysisToUpdate<DominanceFrontier>();
DT = getAnalysisToUpdate<DominatorTree>();
bool Changed = false;
do {
@ -601,11 +620,36 @@ void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond,
++NumTrivial;
}
/// ReplaceLoopExternalDFMember -
/// If BB's dominance frontier has a member that is not part of loop L then
/// remove it. Add NewDFMember in BB's dominance frontier.
void LoopUnswitch::ReplaceLoopExternalDFMember(Loop *L, BasicBlock *BB,
BasicBlock *NewDFMember) {
DominanceFrontier::iterator DFI = DF->find(BB);
if (DFI == DF->end())
return;
DominanceFrontier::DomSetType &DFSet = DFI->second;
for (DominanceFrontier::DomSetType::iterator DI = DFSet.begin(),
DE = DFSet.end(); DI != DE; ++DI) {
BasicBlock *B = *DI;
if (L->contains(B))
continue;
DF->removeFromFrontier(DFI, B);
LoopDF.insert(B);
}
DF->addToFrontier(DFI, NewDFMember);
}
/// SplitExitEdges -
/// Split all of the edges from inside the loop to their exit blocks. Update
/// the appropriate Phi nodes as we do so.
void LoopUnswitch::SplitExitEdges(const SmallVector<BasicBlock *, 8> &ExitBlocks,
void LoopUnswitch::SplitExitEdges(Loop *L, const SmallVector<BasicBlock *, 8> &ExitBlocks,
SmallVector<BasicBlock *, 8> &MiddleBlocks) {
for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
BasicBlock *ExitBlock = ExitBlocks[i];
std::vector<BasicBlock*> Preds(pred_begin(ExitBlock), pred_end(ExitBlock));
@ -622,6 +666,8 @@ void LoopUnswitch::SplitExitEdges(const SmallVector<BasicBlock *, 8> &ExitBlocks
EndBlock = ExitBlock;
}
OrigLoopExitMap[StartBlock] = EndBlock;
std::set<PHINode*> InsertedPHIs;
PHINode* OldLCSSA = 0;
for (BasicBlock::iterator I = EndBlock->begin();
@ -647,8 +693,24 @@ void LoopUnswitch::SplitExitEdges(const SmallVector<BasicBlock *, 8> &ExitBlocks
OldLCSSA->replaceAllUsesWith(NewLCSSA);
NewLCSSA->addIncoming(OldLCSSA, MiddleBlock);
}
if (DF && DT) {
// StartBlock -- > MiddleBlock -- > EndBlock
// StartBlock is loop exiting block. EndBlock will become merge point
// of two loop exits after loop unswitch.
// If StartBlock's DF member includes a block that is not loop member
// then replace that DF member with EndBlock.
// If MiddleBlock's DF member includes a block that is not loop member
// tnen replace that DF member with EndBlock.
ReplaceLoopExternalDFMember(L, StartBlock, EndBlock);
ReplaceLoopExternalDFMember(L, MiddleBlock, EndBlock);
}
}
}
}
/// UnswitchNontrivialCondition - We determined that the loop is profitable
@ -683,7 +745,7 @@ void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val,
// Split all of the edges from inside the loop to their exit blocks. Update
// the appropriate Phi nodes as we do so.
SmallVector<BasicBlock *,8> MiddleBlocks;
SplitExitEdges(ExitBlocks, MiddleBlocks);
SplitExitEdges(L, ExitBlocks, MiddleBlocks);
// The exit blocks may have been changed due to edge splitting, recompute.
ExitBlocks.clear();
@ -692,9 +754,6 @@ void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val,
// Add exit blocks to the loop blocks.
LoopBlocks.insert(LoopBlocks.end(), ExitBlocks.begin(), ExitBlocks.end());
DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>();
DominatorTree *DT = getAnalysisToUpdate<DominatorTree>();
// Next step, clone all of the basic blocks that make up the loop (including
// the loop preheader and exit blocks), keeping track of the mapping between
// the instructions and blocks.
@ -778,6 +837,9 @@ void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val,
// Update dominator info
if (DF && DT) {
SmallVector<BasicBlock *,4> ExitingBlocks;
L->getExitingBlocks(ExitingBlocks);
// Clone dominator info for all cloned basic block.
for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) {
BasicBlock *LBB = LoopBlocks[i];
@ -785,29 +847,57 @@ void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val,
CloneDomInfo(NBB, LBB, NewPreheader, OrigPreheader,
OrigHeader, DT, DF, ValueMap);
// Remove any OutSiders from LBB and NBB's dominance frontier.
DominanceFrontier::iterator LBBI = DF->find(LBB);
if (LBBI != DF->end()) {
DominanceFrontier::DomSetType &LBSet = LBBI->second;
for (DominanceFrontier::DomSetType::iterator LI = LBSet.begin(),
LE = LBSet.end(); LI != LE; /* NULL */) {
BasicBlock *B = *LI++;
if (OutSiders.count(B))
DF->removeFromFrontier(LBBI, B);
}
}
// If LBB's dominance frontier includes DFMember
// such that DFMember is also a member of LoopDF then
// - Remove DFMember from LBB's dominance frontier
// - Copy loop exiting blocks', that are dominated by BB, dominance frontier
// member in BB's dominance frontier
// Remove any OutSiders from LBB and NBB's dominance frontier.
DominanceFrontier::iterator LBBI = DF->find(LBB);
DominanceFrontier::iterator NBBI = DF->find(NBB);
if (NBBI != DF->end()) {
DominanceFrontier::DomSetType NBSet = NBBI->second;
for (DominanceFrontier::DomSetType::iterator NI = NBSet.begin(),
NE = NBSet.end(); NI != NE; /* NULL */) {
BasicBlock *B = *NI++;
if (OutSiders.count(B))
if (LBBI == DF->end())
continue;
DominanceFrontier::DomSetType &LBSet = LBBI->second;
for (DominanceFrontier::DomSetType::iterator LI = LBSet.begin(),
LE = LBSet.end(); LI != LE; /* NULL */) {
BasicBlock *B = *LI++;
if (B == LBB && B == L->getHeader())
continue;
bool removeB = false;
if (!LoopDF.count(B))
continue;
// If LBB dominates loop exits then insert loop exit block's DF
// into B's DF.
for(SmallVector<BasicBlock *, 4>::iterator LExitI = ExitingBlocks.begin(),
LExitE = ExitingBlocks.end(); LExitI != LExitE; ++LExitI) {
BasicBlock *E = *LExitI;
if (!DT->dominates(LBB,E))
continue;
DenseMap<BasicBlock *, BasicBlock *>::iterator DFBI =
OrigLoopExitMap.find(E);
if (DFBI == OrigLoopExitMap.end())
continue;
BasicBlock *DFB = DFBI->second;
DF->addToFrontier(LBBI, DFB);
DF->addToFrontier(NBBI, DFB);
removeB = true;
}
// If B's replacement is inserted in DF then now is the time to remove B.
if (removeB) {
DF->removeFromFrontier(LBBI, B);
if (L->contains(B))
DF->removeFromFrontier(NBBI, cast<BasicBlock>(ValueMap[B]));
else
DF->removeFromFrontier(NBBI, B);
}
}
}
// MiddleBlocks are dominated by original pre header. SplitEdge updated

7
llvm/lib/VMCore/Dominators.cpp
View File

@ -422,8 +422,11 @@ void DominanceFrontier::splitBlock(BasicBlock *NewBB) {
}
if (NewBBI != end()) {
DominanceFrontier::DomSetType NewBBSet = NewBBI->second;
NewBBSet.insert(Set.begin(), Set.end());
for (DominanceFrontier::DomSetType::iterator SetI = Set.begin(),
E = Set.end(); SetI != E; ++SetI) {
BasicBlock *SB = *SetI;
addToFrontier(NewBBI, SB);
}
} else
addBasicBlock(NewBB, Set);
}

29
llvm/test/Transforms/LoopUnswitch/2007-10-04-DomFrontier.ll Normal file
View File

@ -0,0 +1,29 @@
; RUN: llvm-as < %s | opt -licm -loop-unroll -disable-output
@resonant = external global i32 ; <i32*> [#uses=2]
define void @weightadj() {
entry:
br label %bb
bb: ; preds = %bb158, %entry
store i32 0, i32* @resonant, align 4
br i1 false, label %g.exit, label %bb158
g.exit: ; preds = %bb68, %bb
br i1 false, label %bb68, label %cond_true
cond_true: ; preds = %g.exit
store i32 1, i32* @resonant, align 4
br label %bb68
bb68: ; preds = %cond_true, %g.exit
%tmp71 = icmp slt i32 0, 0 ; <i1> [#uses=1]
br i1 %tmp71, label %g.exit, label %bb158
bb158: ; preds = %bb68, %bb
br i1 false, label %bb, label %return
return: ; preds = %bb158
ret void
}