lib/CodeGen/IslExprBuilder.cpp

//===------ IslExprBuilder.cpp ----- Code generate isl AST expressions ----===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
//===----------------------------------------------------------------------===//

#include "polly/CodeGen/IslExprBuilder.h"

#include "polly/Support/GICHelper.h"

#include "llvm/Support/Debug.h"

using namespace llvm;
using namespace polly;

Type *IslExprBuilder::getWidestType(Type *T1, Type *T2) {
  assert(isa<IntegerType>(T1) && isa<IntegerType>(T2));

  if (T1->getPrimitiveSizeInBits() < T2->getPrimitiveSizeInBits())
    return T2;
  else
    return T1;
}

Value *IslExprBuilder::createOpUnary(__isl_take isl_ast_expr *Expr) {
  assert(isl_ast_expr_get_op_type(Expr) == isl_ast_op_minus &&
         "Unsupported unary operation");

  Value *V;
  Type *MaxType = getType(Expr);

  V = create(isl_ast_expr_get_op_arg(Expr, 0));
  MaxType = getWidestType(MaxType, V->getType());

  if (MaxType != V->getType())
    V = Builder.CreateSExt(V, MaxType);

  isl_ast_expr_free(Expr);
  return Builder.CreateNSWNeg(V);
}

Value *IslExprBuilder::createOpNAry(__isl_take isl_ast_expr *Expr) {
  assert(isl_ast_expr_get_type(Expr) == isl_ast_expr_op &&
         "isl ast expression not of type isl_ast_op");
  assert(isl_ast_expr_get_op_n_arg(Expr) >= 2 &&
         "We need at least two operands in an n-ary operation");

  Value *V;

  V = create(isl_ast_expr_get_op_arg(Expr, 0));

  for (int i = 0; i < isl_ast_expr_get_op_n_arg(Expr); ++i) {
    Value *OpV;
    OpV = create(isl_ast_expr_get_op_arg(Expr, i));

    Type *Ty = getWidestType(V->getType(), OpV->getType());

    if (Ty != OpV->getType())
      OpV = Builder.CreateSExt(OpV, Ty);

    if (Ty != V->getType())
      V = Builder.CreateSExt(V, Ty);

    switch (isl_ast_expr_get_op_type(Expr)) {
    default:
      llvm_unreachable("This is no n-ary isl ast expression");

    case isl_ast_op_max: {
      Value *Cmp = Builder.CreateICmpSGT(V, OpV);
      V = Builder.CreateSelect(Cmp, V, OpV);
      continue;
    }
    case isl_ast_op_min: {
      Value *Cmp = Builder.CreateICmpSLT(V, OpV);
      V = Builder.CreateSelect(Cmp, V, OpV);
      continue;
    }
    }
  }

  // TODO: We can truncate the result, if it fits into a smaller type. This can
  // help in cases where we have larger operands (e.g. i67) but the result is
  // known to fit into i64. Without the truncation, the larger i67 type may
  // force all subsequent operations to be performed on a non-native type.
  isl_ast_expr_free(Expr);
  return V;
}

Value *IslExprBuilder::createOpAccess(isl_ast_expr *Expr) {
  assert(isl_ast_expr_get_type(Expr) == isl_ast_expr_op &&
         "isl ast expression not of type isl_ast_op");
  assert(isl_ast_expr_get_op_type(Expr) == isl_ast_op_access &&
         "not an access isl ast expression");
  assert(isl_ast_expr_get_op_n_arg(Expr) >= 2 &&
         "We need at least two operands to create a member access.");

  // TODO: Support for multi-dimensional array.
  assert(isl_ast_expr_get_op_n_arg(Expr) == 2 &&
         "Multidimensional access functions are not supported yet");

  Value *Base, *IndexOp, *Zero, *Access;
  SmallVector<Value *, 4> Indices;
  Type *PtrElTy;

  Base = create(isl_ast_expr_get_op_arg(Expr, 0));
  assert(Base->getType()->isPointerTy() && "Access base should be a pointer");

  IndexOp = create(isl_ast_expr_get_op_arg(Expr, 1));
  assert(IndexOp->getType()->isIntegerTy() &&
         "Access index should be an integer");
  Zero = ConstantInt::getNullValue(IndexOp->getType());

  // If base is a array type like,
  //   int A[N][M][K];
  // we have to adjust the GEP. The easiest way is to transform accesses like,
  //   A[i][j][k]
  // into equivalent ones like,
  //   A[0][0][ i*N*M + j*M + k]
  // because SCEV already folded the "peudo dimensions" into one. Thus our index
  // operand will be 'i*N*M + j*M + k' anyway.
  PtrElTy = Base->getType()->getPointerElementType();
  while (PtrElTy->isArrayTy()) {
    Indices.push_back(Zero);
    PtrElTy = PtrElTy->getArrayElementType();
  }

  Indices.push_back(IndexOp);
  assert((PtrElTy->isIntOrIntVectorTy() || PtrElTy->isFPOrFPVectorTy()) &&
         "We do not yet change the type of the access base during code "
         "generation.");

  Access = Builder.CreateGEP(Base, Indices, "polly.access." + Base->getName());

  isl_ast_expr_free(Expr);
  return Access;
}

Value *IslExprBuilder::createOpBin(__isl_take isl_ast_expr *Expr) {
  Value *LHS, *RHS, *Res;
  Type *MaxType;
  isl_ast_op_type OpType;

  assert(isl_ast_expr_get_type(Expr) == isl_ast_expr_op &&
         "isl ast expression not of type isl_ast_op");
  assert(isl_ast_expr_get_op_n_arg(Expr) == 2 &&
         "not a binary isl ast expression");

  OpType = isl_ast_expr_get_op_type(Expr);

  LHS = create(isl_ast_expr_get_op_arg(Expr, 0));
  RHS = create(isl_ast_expr_get_op_arg(Expr, 1));

  MaxType = LHS->getType();
  MaxType = getWidestType(MaxType, RHS->getType());

  // Take the result into account when calculating the widest type.
  //
  // For operations such as '+' the result may require a type larger than
  // the type of the individual operands. For other operations such as '/', the
  // result type cannot be larger than the type of the individual operand. isl
  // does not calculate correct types for these operations and we consequently
  // exclude those operations here.
  switch (OpType) {
  case isl_ast_op_pdiv_q:
  case isl_ast_op_pdiv_r:
  case isl_ast_op_div:
  case isl_ast_op_fdiv_q:
    // Do nothing
    break;
  case isl_ast_op_add:
  case isl_ast_op_sub:
  case isl_ast_op_mul:
    MaxType = getWidestType(MaxType, getType(Expr));
    break;
  default:
    llvm_unreachable("This is no binary isl ast expression");
  }

  if (MaxType != RHS->getType())
    RHS = Builder.CreateSExt(RHS, MaxType);

  if (MaxType != LHS->getType())
    LHS = Builder.CreateSExt(LHS, MaxType);

  switch (OpType) {
  default:
    llvm_unreachable("This is no binary isl ast expression");
  case isl_ast_op_add:
    Res = Builder.CreateNSWAdd(LHS, RHS);
    break;
  case isl_ast_op_sub:
    Res = Builder.CreateNSWSub(LHS, RHS);
    break;
  case isl_ast_op_mul:
    Res = Builder.CreateNSWMul(LHS, RHS);
    break;
  case isl_ast_op_div:
  case isl_ast_op_pdiv_q: // Dividend is non-negative
    Res = Builder.CreateSDiv(LHS, RHS);
    break;
  case isl_ast_op_fdiv_q: { // Round towards -infty
    // TODO: Review code and check that this calculation does not yield
    //       incorrect overflow in some bordercases.
    //
    // floord(n,d) ((n < 0) ? (n - d + 1) : n) / d
    Value *One = ConstantInt::get(MaxType, 1);
    Value *Zero = ConstantInt::get(MaxType, 0);
    Value *Sum1 = Builder.CreateSub(LHS, RHS);
    Value *Sum2 = Builder.CreateAdd(Sum1, One);
    Value *isNegative = Builder.CreateICmpSLT(LHS, Zero);
    Value *Dividend = Builder.CreateSelect(isNegative, Sum2, LHS);
    Res = Builder.CreateSDiv(Dividend, RHS);
    break;
  }
  case isl_ast_op_pdiv_r: // Dividend is non-negative
    Res = Builder.CreateSRem(LHS, RHS);
    break;
  }

  // TODO: We can truncate the result, if it fits into a smaller type. This can
  // help in cases where we have larger operands (e.g. i67) but the result is
  // known to fit into i64. Without the truncation, the larger i67 type may
  // force all subsequent operations to be performed on a non-native type.
  isl_ast_expr_free(Expr);
  return Res;
}

Value *IslExprBuilder::createOpSelect(__isl_take isl_ast_expr *Expr) {
  assert(isl_ast_expr_get_op_type(Expr) == isl_ast_op_select &&
         "Unsupported unary isl ast expression");
  Value *LHS, *RHS, *Cond;
  Type *MaxType = getType(Expr);

  Cond = create(isl_ast_expr_get_op_arg(Expr, 0));

  LHS = create(isl_ast_expr_get_op_arg(Expr, 1));
  RHS = create(isl_ast_expr_get_op_arg(Expr, 2));

  MaxType = getWidestType(MaxType, LHS->getType());
  MaxType = getWidestType(MaxType, RHS->getType());

  if (MaxType != RHS->getType())
    RHS = Builder.CreateSExt(RHS, MaxType);

  if (MaxType != LHS->getType())
    LHS = Builder.CreateSExt(LHS, MaxType);

  // TODO: Do we want to truncate the result?
  isl_ast_expr_free(Expr);
  return Builder.CreateSelect(Cond, LHS, RHS);
}

Value *IslExprBuilder::createOpICmp(__isl_take isl_ast_expr *Expr) {
  assert(isl_ast_expr_get_type(Expr) == isl_ast_expr_op &&
         "Expected an isl_ast_expr_op expression");

  Value *LHS, *RHS, *Res;

  LHS = create(isl_ast_expr_get_op_arg(Expr, 0));
  RHS = create(isl_ast_expr_get_op_arg(Expr, 1));

  Type *MaxType = LHS->getType();
  MaxType = getWidestType(MaxType, RHS->getType());

  if (MaxType != RHS->getType())
    RHS = Builder.CreateSExt(RHS, MaxType);

  if (MaxType != LHS->getType())
    LHS = Builder.CreateSExt(LHS, MaxType);

  switch (isl_ast_expr_get_op_type(Expr)) {
  default:
    llvm_unreachable("Unsupported ICmp isl ast expression");
  case isl_ast_op_eq:
    Res = Builder.CreateICmpEQ(LHS, RHS);
    break;
  case isl_ast_op_le:
    Res = Builder.CreateICmpSLE(LHS, RHS);
    break;
  case isl_ast_op_lt:
    Res = Builder.CreateICmpSLT(LHS, RHS);
    break;
  case isl_ast_op_ge:
    Res = Builder.CreateICmpSGE(LHS, RHS);
    break;
  case isl_ast_op_gt:
    Res = Builder.CreateICmpSGT(LHS, RHS);
    break;
  }

  isl_ast_expr_free(Expr);
  return Res;
}

Value *IslExprBuilder::createOpBoolean(__isl_take isl_ast_expr *Expr) {
  assert(isl_ast_expr_get_type(Expr) == isl_ast_expr_op &&
         "Expected an isl_ast_expr_op expression");

  Value *LHS, *RHS, *Res;
  isl_ast_op_type OpType;

  OpType = isl_ast_expr_get_op_type(Expr);

  assert((OpType == isl_ast_op_and || OpType == isl_ast_op_or) &&
         "Unsupported isl_ast_op_type");

  LHS = create(isl_ast_expr_get_op_arg(Expr, 0));
  RHS = create(isl_ast_expr_get_op_arg(Expr, 1));

  // Even though the isl pretty printer prints the expressions as 'exp && exp'
  // or 'exp || exp', we actually code generate the bitwise expressions
  // 'exp & exp' or 'exp | exp'. This forces the evaluation of both branches,
  // but it is, due to the use of i1 types, otherwise equivalent. The reason
  // to go for bitwise operations is, that we assume the reduced control flow
  // will outweight the overhead introduced by evaluating unneeded expressions.
  // The isl code generation currently does not take advantage of the fact that
  // the expression after an '||' or '&&' is in some cases not evaluated.
  // Evaluating it anyways does not cause any undefined behaviour.
  //
  // TODO: Document in isl itself, that the unconditionally evaluating the
  // second part of '||' or '&&' expressions is safe.
  assert(LHS->getType() == Builder.getInt1Ty() && "Expected i1 type");
  assert(RHS->getType() == Builder.getInt1Ty() && "Expected i1 type");

  switch (OpType) {
  default:
    llvm_unreachable("Unsupported boolean expression");
  case isl_ast_op_and:
    Res = Builder.CreateAnd(LHS, RHS);
    break;
  case isl_ast_op_or:
    Res = Builder.CreateOr(LHS, RHS);
    break;
  }

  isl_ast_expr_free(Expr);
  return Res;
}

Value *IslExprBuilder::createOp(__isl_take isl_ast_expr *Expr) {
  assert(isl_ast_expr_get_type(Expr) == isl_ast_expr_op &&
         "Expression not of type isl_ast_expr_op");
  switch (isl_ast_expr_get_op_type(Expr)) {
  case isl_ast_op_error:
  case isl_ast_op_cond:
  case isl_ast_op_and_then:
  case isl_ast_op_or_else:
  case isl_ast_op_call:
  case isl_ast_op_member:
    llvm_unreachable("Unsupported isl ast expression");
  case isl_ast_op_access:
    return createOpAccess(Expr);
  case isl_ast_op_max:
  case isl_ast_op_min:
    return createOpNAry(Expr);
  case isl_ast_op_add:
  case isl_ast_op_sub:
  case isl_ast_op_mul:
  case isl_ast_op_div:
  case isl_ast_op_fdiv_q: // Round towards -infty
  case isl_ast_op_pdiv_q: // Dividend is non-negative
  case isl_ast_op_pdiv_r: // Dividend is non-negative
    return createOpBin(Expr);
  case isl_ast_op_minus:
    return createOpUnary(Expr);
  case isl_ast_op_select:
    return createOpSelect(Expr);
  case isl_ast_op_and:
  case isl_ast_op_or:
    return createOpBoolean(Expr);
  case isl_ast_op_eq:
  case isl_ast_op_le:
  case isl_ast_op_lt:
  case isl_ast_op_ge:
  case isl_ast_op_gt:
    return createOpICmp(Expr);
  }

  llvm_unreachable("Unsupported isl_ast_expr_op kind.");
}

Value *IslExprBuilder::createId(__isl_take isl_ast_expr *Expr) {
  assert(isl_ast_expr_get_type(Expr) == isl_ast_expr_id &&
         "Expression not of type isl_ast_expr_ident");

  isl_id *Id;
  Value *V;

  Id = isl_ast_expr_get_id(Expr);

  assert(IDToValue.count(Id) && "Identifier not found");

  V = IDToValue[Id];

  isl_id_free(Id);
  isl_ast_expr_free(Expr);

  return V;
}

IntegerType *IslExprBuilder::getType(__isl_keep isl_ast_expr *Expr) {
  // XXX: We assume i64 is large enough. This is often true, but in general
  //      incorrect. Also, on 32bit architectures, it would be beneficial to
  //      use a smaller type. We can and should directly derive this information
  //      during code generation.
  return IntegerType::get(Builder.getContext(), 64);
}

Value *IslExprBuilder::createInt(__isl_take isl_ast_expr *Expr) {
  assert(isl_ast_expr_get_type(Expr) == isl_ast_expr_int &&
         "Expression not of type isl_ast_expr_int");
  isl_val *Val;
  Value *V;
  APInt APValue;
  IntegerType *T;

  Val = isl_ast_expr_get_val(Expr);
  APValue = APIntFromVal(Val);
  T = getType(Expr);
  APValue = APValue.sextOrSelf(T->getBitWidth());
  V = ConstantInt::get(T, APValue);

  isl_ast_expr_free(Expr);
  return V;
}

Value *IslExprBuilder::create(__isl_take isl_ast_expr *Expr) {
  switch (isl_ast_expr_get_type(Expr)) {
  case isl_ast_expr_error:
    llvm_unreachable("Code generation error");
  case isl_ast_expr_op:
    return createOp(Expr);
  case isl_ast_expr_id:
    return createId(Expr);
  case isl_ast_expr_int:
    return createInt(Expr);
  }

  llvm_unreachable("Unexpected enum value");
}