Commit 5dbed5dc authored by Tobias Grosser's avatar Tobias Grosser
Browse files

LoopGenerators: Construct loops such that they are already loop rotated 

                BeforeBB
                   |
                   v
                GuardBB
                /      \
       __  PreHeaderBB  \
      /  \    /         |
   latch  HeaderBB      |
      \  /    \         /
       <       \       /
                \     /
                ExitBB

This does not only remove the need for an explicit loop rotate pass, but it also
gives us the possibility to skip the construction of the guard condition in case
the loop is known to be executed at least once. We do not yet exploit this, but
by implementing this analysis in the isl code generator we should be able to
remove more guards than the generic loop rotate pass can.  Another point is that
loop rotation can introduce additional PHI nodes, which may hide that a loop can
be executed in parallel. This change avoids this complication and will make it
easier to move the openmp code generation into a separate pass.

Merged from https://llvm.org/svn/llvm-project/polly/trunk@181986

llvm-svn: 183373
parent 3aeb1b7a

polly/include/polly/CodeGen/LoopGenerators.h

+2 −1
Original line number Diff line number Diff line
@@ -36,10 +36,11 @@ using namespace llvm; 
/// @param Builder    The builder used to create the loop.

/// @param P          A pointer to the pass that uses this function. It is used

///                   to update analysis information.

/// @param ExitBlock  The block the loop will exit to.

/// @param Predicate  The predicate used to generate the upper loop bound.

/// @return Value*    The newly created induction variable for this loop.

Value *createLoop(Value *LowerBound, Value *UpperBound, Value *Stride,

                  IRBuilder<> &Builder, Pass *P, BasicBlock *&AfterBlock,

                  IRBuilder<> &Builder, Pass *P, BasicBlock *&ExitBlock,

                  ICmpInst::Predicate Predicate);



class OMPGenerator {

polly/lib/CodeGen/CodeGeneration.cpp

+3 −3
Original line number Diff line number Diff line
@@ -468,14 +468,14 @@ void ClastStmtCodeGen::codegen(const clast_block *b) { 


void ClastStmtCodeGen::codegenForSequential(const clast_for *f) {

  Value *LowerBound, *UpperBound, *IV, *Stride;

  BasicBlock *AfterBB;

  BasicBlock *ExitBlock;

  Type *IntPtrTy = getIntPtrTy();



  LowerBound = ExpGen.codegen(f->LB, IntPtrTy);

  UpperBound = ExpGen.codegen(f->UB, IntPtrTy);

  Stride = Builder.getInt(APInt_from_MPZ(f->stride));



  IV = createLoop(LowerBound, UpperBound, Stride, Builder, P, AfterBB,

  IV = createLoop(LowerBound, UpperBound, Stride, Builder, P, ExitBlock,

                  CmpInst::ICMP_SLE);



  // Add loop iv to symbols.
@@ -486,7 +486,7 @@ void ClastStmtCodeGen::codegenForSequential(const clast_for *f) { 


  // Loop is finished, so remove its iv from the live symbols.

  ClastVars.erase(f->iterator);

  Builder.SetInsertPoint(AfterBB->begin());

  Builder.SetInsertPoint(ExitBlock->begin());

}



// Helper class to determine all scalar parameters used in the basic blocks of a

polly/lib/CodeGen/IslCodeGeneration.cpp

+3 −10
Original line number Diff line number Diff line
@@ -780,7 +780,7 @@ void IslNodeBuilder::createForSequential(__isl_take isl_ast_node *For) { 
  isl_id *IteratorID;

  Value *ValueLB, *ValueUB, *ValueInc;

  Type *MaxType;

  BasicBlock *AfterBlock;

  BasicBlock *ExitBlock;

  Value *IV;

  CmpInst::Predicate Predicate;
@@ -814,21 +814,14 @@ void IslNodeBuilder::createForSequential(__isl_take isl_ast_node *For) { 
  if (MaxType != ValueInc->getType())

    ValueInc = Builder.CreateSExt(ValueInc, MaxType);



  // TODO: In case we can proof a loop is executed at least once, we can

  //       generate the condition iv != UB + stride (consider possible

  //       overflow). This condition will allow LLVM to prove the loop is

  //       executed at least once, which will enable a lot of loop invariant

  //       code motion.



  IV =

      createLoop(ValueLB, ValueUB, ValueInc, Builder, P, AfterBlock, Predicate);

  IV = createLoop(ValueLB, ValueUB, ValueInc, Builder, P, ExitBlock, Predicate);

  IDToValue[IteratorID] = IV;



  create(Body);



  IDToValue.erase(IteratorID);



  Builder.SetInsertPoint(AfterBlock->begin());

  Builder.SetInsertPoint(ExitBlock->begin());



  isl_ast_node_free(For);

  isl_ast_expr_free(Iterator);

polly/lib/CodeGen/LoopGenerators.cpp

+67 −36
Original line number Diff line number Diff line
@@ -22,53 +22,84 @@ 
using namespace llvm;

using namespace polly;



// We generate a loop of the following structure

//

//              BeforeBB

//                 |

//                 v

//              GuardBB

//              /      \

//     __  PreHeaderBB  \

//    /  \    /         |

// latch  HeaderBB      |

//    \  /    \         /

//     <       \       /

//              \     /

//              ExitBB

//

// GuardBB checks if the loop is executed at least once. If this is the case

// we branch to PreHeaderBB and subsequently to the HeaderBB, which contains the

// loop iv 'polly.indvar', the incremented loop iv 'polly.indvar_next' as well

// as the condition to check if we execute another iteration of the loop. After

// the loop has finished, we branch to ExitBB.

//

// TODO: We currently always create the GuardBB. If we can prove the loop is

//       always executed at least once, we can get rid of this branch.

Value *polly::createLoop(Value *LB, Value *UB, Value *Stride,

                         IRBuilder<> &Builder, Pass *P, BasicBlock *&AfterBlock,

                         IRBuilder<> &Builder, Pass *P, BasicBlock *&ExitBB,

                         ICmpInst::Predicate Predicate) {



  DominatorTree &DT = P->getAnalysis<DominatorTree>();

  Function *F = Builder.GetInsertBlock()->getParent();

  LLVMContext &Context = F->getContext();



  BasicBlock *PreheaderBB = Builder.GetInsertBlock();

  BasicBlock *HeaderBB = BasicBlock::Create(Context, "polly.loop_header", F);

  BasicBlock *BodyBB = BasicBlock::Create(Context, "polly.loop_body", F);

  BasicBlock *AfterBB = SplitBlock(PreheaderBB, Builder.GetInsertPoint()++, P);

  AfterBB->setName("polly.loop_after");



  PreheaderBB->getTerminator()->setSuccessor(0, HeaderBB);

  DT.addNewBlock(HeaderBB, PreheaderBB);



  Builder.SetInsertPoint(HeaderBB);



  // Use the type of upper and lower bound.

  assert(LB->getType() == UB->getType() &&

         "Different types for upper and lower bound.");



  assert(LB->getType() == UB->getType() && "Types of loop bounds do not match");

  IntegerType *LoopIVType = dyn_cast<IntegerType>(UB->getType());

  assert(LoopIVType && "UB is not integer?");



  // IV

  PHINode *IV = Builder.CreatePHI(LoopIVType, 2, "polly.loopiv");

  IV->addIncoming(LB, PreheaderBB);



  Stride = Builder.CreateZExtOrBitCast(Stride, LoopIVType);

  Value *IncrementedIV = Builder.CreateNSWAdd(IV, Stride, "polly.next_loopiv");



  // Exit condition.

  Value *CMP;

  CMP = Builder.CreateICmp(Predicate, IV, UB);



  Builder.CreateCondBr(CMP, BodyBB, AfterBB);

  DT.addNewBlock(BodyBB, HeaderBB);



  Builder.SetInsertPoint(BodyBB);

  BasicBlock *BeforeBB = Builder.GetInsertBlock();

  BasicBlock *GuardBB = BasicBlock::Create(Context, "polly.loop_if", F);

  BasicBlock *HeaderBB = BasicBlock::Create(Context, "polly.loop_header", F);

  BasicBlock *PreHeaderBB =

      BasicBlock::Create(Context, "polly.loop_preheader", F);



  // ExitBB

  ExitBB = SplitBlock(BeforeBB, Builder.GetInsertPoint()++, P);

  ExitBB->setName("polly.loop_exit");



  // BeforeBB

  BeforeBB->getTerminator()->setSuccessor(0, GuardBB);



  // GuardBB

  DT.addNewBlock(GuardBB, BeforeBB);

  Builder.SetInsertPoint(GuardBB);

  Value *LoopGuard;

  LoopGuard = Builder.CreateICmp(Predicate, LB, UB);

  LoopGuard->setName("polly.loop_guard");

  Builder.CreateCondBr(LoopGuard, PreHeaderBB, ExitBB);



  // PreHeaderBB

  DT.addNewBlock(PreHeaderBB, GuardBB);

  Builder.SetInsertPoint(PreHeaderBB);

  Builder.CreateBr(HeaderBB);

  IV->addIncoming(IncrementedIV, BodyBB);

  DT.changeImmediateDominator(AfterBB, HeaderBB);



  Builder.SetInsertPoint(BodyBB->begin());

  AfterBlock = AfterBB;



  // HeaderBB

  DT.addNewBlock(HeaderBB, PreHeaderBB);

  Builder.SetInsertPoint(HeaderBB);

  PHINode *IV = Builder.CreatePHI(LoopIVType, 2, "polly.indvar");

  IV->addIncoming(LB, PreHeaderBB);

  Stride = Builder.CreateZExtOrBitCast(Stride, LoopIVType);

  Value *IncrementedIV = Builder.CreateNSWAdd(IV, Stride, "polly.indvar_next");

  Value *LoopCondition;

  UB = Builder.CreateSub(UB, Stride, "polly.adjust_ub");

  LoopCondition = Builder.CreateICmp(Predicate, IV, UB);

  LoopCondition->setName("polly.loop_cond");

  Builder.CreateCondBr(LoopCondition, HeaderBB, ExitBB);

  IV->addIncoming(IncrementedIV, HeaderBB);

  DT.changeImmediateDominator(ExitBB, GuardBB);



  // The loop body should be added here.

  Builder.SetInsertPoint(HeaderBB->getFirstNonPHI());

  return IV;

}

polly/test/Cloog/CodeGen/MemAccess/codegen_simple_md.ll

+6 −6
Original line number Diff line number Diff line
@@ -59,16 +59,16 @@ for.end6: ; preds = %for.cond 
; WITHCONST:  %p_mul_coeff = mul i64 16, [[REG1]]

; WITHCONST:  %p_sum_coeff = add i64 5, %p_mul_coeff

; WITHCONST:  [[REG2:%[0-9]+]] = sext i32 %{{[0-9]+}} to i64

; WITHCONST:  %p_mul_coeff6 = mul i64 2, [[REG2]]

; WITHCONST:  %p_sum_coeff7 = add i64 %p_sum_coeff, %p_mul_coeff6

; WITHCONST:  %p_newarrayidx_ = getelementptr [1040 x i32]* @A, i64 0, i64 %p_sum_coeff7

; WITHCONST:  %p_mul_coeff8 = mul i64 2, [[REG2]]

; WITHCONST:  %p_sum_coeff9 = add i64 %p_sum_coeff, %p_mul_coeff8

; WITHCONST:  %p_newarrayidx_ = getelementptr [1040 x i32]* @A, i64 0, i64 %p_sum_coeff9

; WITHCONST:  store i32 100, i32* %p_newarrayidx_



; WITHOUTCONST:  [[REG1:%[0-9]+]] = sext i32 %{{[0-9]+}} to i64

; WITHOUTCONST:  %p_mul_coeff = mul i64 16, [[REG1]]

; WITHOUTCONST:  %p_sum_coeff = add i64 0, %p_mul_coeff

; WITHOUTCONST:  [[REG2:%[0-9]+]] = sext i32 %{{[0-9]+}} to i64

; WITHOUTCONST:  %p_mul_coeff6 = mul i64 2, [[REG2]]

; WITHOUTCONST:  %p_sum_coeff7 = add i64 %p_sum_coeff, %p_mul_coeff6

; WITHOUTCONST:  %p_newarrayidx_ = getelementptr [1040 x i32]* @A, i64 0, i64 %p_sum_coeff7

; WITHOUTCONST:  %p_mul_coeff8 = mul i64 2, [[REG2]]

; WITHOUTCONST:  %p_sum_coeff9 = add i64 %p_sum_coeff, %p_mul_coeff8

; WITHOUTCONST:  %p_newarrayidx_ = getelementptr [1040 x i32]* @A, i64 0, i64 %p_sum_coeff9

; WITHOUTCONST:  store i32 100, i32* %p_newarrayidx_