lib/CodeGen/IntrinsicLowering.cpp

   1 //===-- IntrinsicLowering.cpp - Intrinsic Lowering default implementation -===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This file implements the IntrinsicLowering class.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "llvm/Constants.h"
  15 #include "llvm/DerivedTypes.h"
  16 #include "llvm/Module.h"
  17 #include "llvm/Type.h"
  18 #include "llvm/CodeGen/IntrinsicLowering.h"
  19 #include "llvm/Support/IRBuilder.h"
  20 #include "llvm/Support/ErrorHandling.h"
  21 #include "llvm/Target/TargetData.h"
  22 #include "llvm/ADT/SmallVector.h"
  23 using namespace llvm;
  24
  25 template <class ArgIt>
  26 static void EnsureFunctionExists(Module &M, const char *Name,
  27                                  ArgIt ArgBegin, ArgIt ArgEnd,
  28                                  const Type *RetTy) {
  29   // Insert a correctly-typed definition now.
  30   std::vector<const Type *> ParamTys;
  31   for (ArgIt I = ArgBegin; I != ArgEnd; ++I)
  32     ParamTys.push_back(I->getType());
  33   M.getOrInsertFunction(Name, FunctionType::get(RetTy, ParamTys, false));
  34 }
  35
  36 static void EnsureFPIntrinsicsExist(Module &M, Function *Fn,
  37                                     const char *FName,
  38                                     const char *DName, const char *LDName) {
  39   // Insert definitions for all the floating point types.
  40   switch((int)Fn->arg_begin()->getType()->getTypeID()) {
  41   case Type::FloatTyID:
  42     EnsureFunctionExists(M, FName, Fn->arg_begin(), Fn->arg_end(),
  43                          Type::FloatTy);
  44     break;
  45   case Type::DoubleTyID:
  46     EnsureFunctionExists(M, DName, Fn->arg_begin(), Fn->arg_end(),
  47                          Type::DoubleTy);
  48     break;
  49   case Type::X86_FP80TyID:
  50   case Type::FP128TyID:
  51   case Type::PPC_FP128TyID:
  52     EnsureFunctionExists(M, LDName, Fn->arg_begin(), Fn->arg_end(),
  53                          Fn->arg_begin()->getType());
  54     break;
  55   }
  56 }
  57
  58 /// ReplaceCallWith - This function is used when we want to lower an intrinsic
  59 /// call to a call of an external function.  This handles hard cases such as
  60 /// when there was already a prototype for the external function, and if that
  61 /// prototype doesn't match the arguments we expect to pass in.
  62 template <class ArgIt>
  63 static CallInst *ReplaceCallWith(const char *NewFn, CallInst *CI,
  64                                  ArgIt ArgBegin, ArgIt ArgEnd,
  65                                  const Type *RetTy) {
  66   // If we haven't already looked up this function, check to see if the
  67   // program already contains a function with this name.
  68   Module *M = CI->getParent()->getParent()->getParent();
  69   // Get or insert the definition now.
  70   std::vector<const Type *> ParamTys;
  71   for (ArgIt I = ArgBegin; I != ArgEnd; ++I)
  72     ParamTys.push_back((*I)->getType());
  73   Constant* FCache = M->getOrInsertFunction(NewFn,
  74                                   FunctionType::get(RetTy, ParamTys, false));
  75
  76   IRBuilder<> Builder(CI->getParent(), CI);
  77   SmallVector<Value *, 8> Args(ArgBegin, ArgEnd);
  78   CallInst *NewCI = Builder.CreateCall(FCache, Args.begin(), Args.end());
  79   NewCI->setName(CI->getName());
  80   if (!CI->use_empty())
  81     CI->replaceAllUsesWith(NewCI);
  82   return NewCI;
  83 }
  84
  85 void IntrinsicLowering::AddPrototypes(Module &M) {
  86   for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
  87     if (I->isDeclaration() && !I->use_empty())
  88       switch (I->getIntrinsicID()) {
  89       default: break;
  90       case Intrinsic::setjmp:
  91         EnsureFunctionExists(M, "setjmp", I->arg_begin(), I->arg_end(),
  92                              Type::Int32Ty);
  93         break;
  94       case Intrinsic::longjmp:
  95         EnsureFunctionExists(M, "longjmp", I->arg_begin(), I->arg_end(),
  96                              Type::VoidTy);
  97         break;
  98       case Intrinsic::siglongjmp:
  99         EnsureFunctionExists(M, "abort", I->arg_end(), I->arg_end(),
 100                              Type::VoidTy);
 101         break;
 102       case Intrinsic::memcpy:
 103         M.getOrInsertFunction("memcpy", PointerType::getUnqual(Type::Int8Ty),
 104                               PointerType::getUnqual(Type::Int8Ty),
 105                               PointerType::getUnqual(Type::Int8Ty),
 106                               TD.getIntPtrType(), (Type *)0);
 107         break;
 108       case Intrinsic::memmove:
 109         M.getOrInsertFunction("memmove", PointerType::getUnqual(Type::Int8Ty),
 110                               PointerType::getUnqual(Type::Int8Ty),
 111                               PointerType::getUnqual(Type::Int8Ty),
 112                               TD.getIntPtrType(), (Type *)0);
 113         break;
 114       case Intrinsic::memset:
 115         M.getOrInsertFunction("memset", PointerType::getUnqual(Type::Int8Ty),
 116                               PointerType::getUnqual(Type::Int8Ty),
 117                               Type::Int32Ty,
 118                               TD.getIntPtrType(), (Type *)0);
 119         break;
 120       case Intrinsic::sqrt:
 121         EnsureFPIntrinsicsExist(M, I, "sqrtf", "sqrt", "sqrtl");
 122         break;
 123       case Intrinsic::sin:
 124         EnsureFPIntrinsicsExist(M, I, "sinf", "sin", "sinl");
 125         break;
 126       case Intrinsic::cos:
 127         EnsureFPIntrinsicsExist(M, I, "cosf", "cos", "cosl");
 128         break;
 129       case Intrinsic::pow:
 130         EnsureFPIntrinsicsExist(M, I, "powf", "pow", "powl");
 131         break;
 132       case Intrinsic::log:
 133         EnsureFPIntrinsicsExist(M, I, "logf", "log", "logl");
 134         break;
 135       case Intrinsic::log2:
 136         EnsureFPIntrinsicsExist(M, I, "log2f", "log2", "log2l");
 137         break;
 138       case Intrinsic::log10:
 139         EnsureFPIntrinsicsExist(M, I, "log10f", "log10", "log10l");
 140         break;
 141       case Intrinsic::exp:
 142         EnsureFPIntrinsicsExist(M, I, "expf", "exp", "expl");
 143         break;
 144       case Intrinsic::exp2:
 145         EnsureFPIntrinsicsExist(M, I, "exp2f", "exp2", "exp2l");
 146         break;
 147       }
 148 }
 149
 150 /// LowerBSWAP - Emit the code to lower bswap of V before the specified
 151 /// instruction IP.
 152 static Value *LowerBSWAP(LLVMContext &Context, Value *V, Instruction *IP) {
 153   assert(V->getType()->isInteger() && "Can't bswap a non-integer type!");
 154
 155   unsigned BitSize = V->getType()->getPrimitiveSizeInBits();
 156
 157   IRBuilder<> Builder(IP->getParent(), IP);
 158
 159   switch(BitSize) {
 160   default: llvm_unreachable("Unhandled type size of value to byteswap!");
 161   case 16: {
 162     Value *Tmp1 = Builder.CreateShl(V, Context.getConstantInt(V->getType(), 8),
 163                                     "bswap.2");
 164     Value *Tmp2 = Builder.CreateLShr(V, Context.getConstantInt(V->getType(), 8),
 165                                      "bswap.1");
 166     V = Builder.CreateOr(Tmp1, Tmp2, "bswap.i16");
 167     break;
 168   }
 169   case 32: {
 170     Value *Tmp4 = Builder.CreateShl(V, Context.getConstantInt(V->getType(), 24),
 171                                     "bswap.4");
 172     Value *Tmp3 = Builder.CreateShl(V, Context.getConstantInt(V->getType(), 8),
 173                                     "bswap.3");
 174     Value *Tmp2 = Builder.CreateLShr(V, Context.getConstantInt(V->getType(), 8),
 175                                      "bswap.2");
 176     Value *Tmp1 = Builder.CreateLShr(V,Context.getConstantInt(V->getType(), 24),
 177                                      "bswap.1");
 178     Tmp3 = Builder.CreateAnd(Tmp3,
 179                              Context.getConstantInt(Type::Int32Ty, 0xFF0000),
 180                              "bswap.and3");
 181     Tmp2 = Builder.CreateAnd(Tmp2,
 182                              Context.getConstantInt(Type::Int32Ty, 0xFF00),
 183                              "bswap.and2");
 184     Tmp4 = Builder.CreateOr(Tmp4, Tmp3, "bswap.or1");
 185     Tmp2 = Builder.CreateOr(Tmp2, Tmp1, "bswap.or2");
 186     V = Builder.CreateOr(Tmp4, Tmp2, "bswap.i32");
 187     break;
 188   }
 189   case 64: {
 190     Value *Tmp8 = Builder.CreateShl(V, Context.getConstantInt(V->getType(), 56),
 191                                     "bswap.8");
 192     Value *Tmp7 = Builder.CreateShl(V, Context.getConstantInt(V->getType(), 40),
 193                                     "bswap.7");
 194     Value *Tmp6 = Builder.CreateShl(V, Context.getConstantInt(V->getType(), 24),
 195                                     "bswap.6");
 196     Value *Tmp5 = Builder.CreateShl(V, Context.getConstantInt(V->getType(), 8),
 197                                     "bswap.5");
 198     Value* Tmp4 = Builder.CreateLShr(V, Context.getConstantInt(V->getType(), 8),
 199                                      "bswap.4");
 200     Value* Tmp3 = Builder.CreateLShr(V,
 201                                      Context.getConstantInt(V->getType(), 24),
 202                                      "bswap.3");
 203     Value* Tmp2 = Builder.CreateLShr(V,
 204                                      Context.getConstantInt(V->getType(), 40),
 205                                      "bswap.2");
 206     Value* Tmp1 = Builder.CreateLShr(V,
 207                                      Context.getConstantInt(V->getType(), 56),
 208                                      "bswap.1");
 209     Tmp7 = Builder.CreateAnd(Tmp7,
 210                              Context.getConstantInt(Type::Int64Ty,
 211                                               0xFF000000000000ULL),
 212                              "bswap.and7");
 213     Tmp6 = Builder.CreateAnd(Tmp6,
 214                              Context.getConstantInt(Type::Int64Ty,
 215                                               0xFF0000000000ULL),
 216                              "bswap.and6");
 217     Tmp5 = Builder.CreateAnd(Tmp5,
 218                         Context.getConstantInt(Type::Int64Ty, 0xFF00000000ULL),
 219                              "bswap.and5");
 220     Tmp4 = Builder.CreateAnd(Tmp4,
 221                         Context.getConstantInt(Type::Int64Ty, 0xFF000000ULL),
 222                              "bswap.and4");
 223     Tmp3 = Builder.CreateAnd(Tmp3,
 224                              Context.getConstantInt(Type::Int64Ty, 0xFF0000ULL),
 225                              "bswap.and3");
 226     Tmp2 = Builder.CreateAnd(Tmp2,
 227                              Context.getConstantInt(Type::Int64Ty, 0xFF00ULL),
 228                              "bswap.and2");
 229     Tmp8 = Builder.CreateOr(Tmp8, Tmp7, "bswap.or1");
 230     Tmp6 = Builder.CreateOr(Tmp6, Tmp5, "bswap.or2");
 231     Tmp4 = Builder.CreateOr(Tmp4, Tmp3, "bswap.or3");
 232     Tmp2 = Builder.CreateOr(Tmp2, Tmp1, "bswap.or4");
 233     Tmp8 = Builder.CreateOr(Tmp8, Tmp6, "bswap.or5");
 234     Tmp4 = Builder.CreateOr(Tmp4, Tmp2, "bswap.or6");
 235     V = Builder.CreateOr(Tmp8, Tmp4, "bswap.i64");
 236     break;
 237   }
 238   }
 239   return V;
 240 }
 241
 242 /// LowerCTPOP - Emit the code to lower ctpop of V before the specified
 243 /// instruction IP.
 244 static Value *LowerCTPOP(LLVMContext &Context, Value *V, Instruction *IP) {
 245   assert(V->getType()->isInteger() && "Can't ctpop a non-integer type!");
 246
 247   static const uint64_t MaskValues[6] = {
 248     0x5555555555555555ULL, 0x3333333333333333ULL,
 249     0x0F0F0F0F0F0F0F0FULL, 0x00FF00FF00FF00FFULL,
 250     0x0000FFFF0000FFFFULL, 0x00000000FFFFFFFFULL
 251   };
 252
 253   IRBuilder<> Builder(IP->getParent(), IP);
 254
 255   unsigned BitSize = V->getType()->getPrimitiveSizeInBits();
 256   unsigned WordSize = (BitSize + 63) / 64;
 257   Value *Count = Context.getConstantInt(V->getType(), 0);
 258
 259   for (unsigned n = 0; n < WordSize; ++n) {
 260     Value *PartValue = V;
 261     for (unsigned i = 1, ct = 0; i < (BitSize>64 ? 64 : BitSize);
 262          i <<= 1, ++ct) {
 263       Value *MaskCst = Context.getConstantInt(V->getType(), MaskValues[ct]);
 264       Value *LHS = Builder.CreateAnd(PartValue, MaskCst, "cppop.and1");
 265       Value *VShift = Builder.CreateLShr(PartValue,
 266                                         Context.getConstantInt(V->getType(), i),
 267                                          "ctpop.sh");
 268       Value *RHS = Builder.CreateAnd(VShift, MaskCst, "cppop.and2");
 269       PartValue = Builder.CreateAdd(LHS, RHS, "ctpop.step");
 270     }
 271     Count = Builder.CreateAdd(PartValue, Count, "ctpop.part");
 272     if (BitSize > 64) {
 273       V = Builder.CreateLShr(V, Context.getConstantInt(V->getType(), 64),
 274                              "ctpop.part.sh");
 275       BitSize -= 64;
 276     }
 277   }
 278
 279   return Count;
 280 }
 281
 282 /// LowerCTLZ - Emit the code to lower ctlz of V before the specified
 283 /// instruction IP.
 284 static Value *LowerCTLZ(LLVMContext &Context, Value *V, Instruction *IP) {
 285
 286   IRBuilder<> Builder(IP->getParent(), IP);
 287
 288   unsigned BitSize = V->getType()->getPrimitiveSizeInBits();
 289   for (unsigned i = 1; i < BitSize; i <<= 1) {
 290     Value *ShVal = Context.getConstantInt(V->getType(), i);
 291     ShVal = Builder.CreateLShr(V, ShVal, "ctlz.sh");
 292     V = Builder.CreateOr(V, ShVal, "ctlz.step");
 293   }
 294
 295   V = Builder.CreateNot(V);
 296   return LowerCTPOP(Context, V, IP);
 297 }
 298
 299 static void ReplaceFPIntrinsicWithCall(CallInst *CI, const char *Fname,
 300                                        const char *Dname,
 301                                        const char *LDname) {
 302   switch (CI->getOperand(1)->getType()->getTypeID()) {
 303   default: llvm_unreachable("Invalid type in intrinsic");
 304   case Type::FloatTyID:
 305     ReplaceCallWith(Fname, CI, CI->op_begin() + 1, CI->op_end(),
 306                   Type::FloatTy);
 307     break;
 308   case Type::DoubleTyID:
 309     ReplaceCallWith(Dname, CI, CI->op_begin() + 1, CI->op_end(),
 310                   Type::DoubleTy);
 311     break;
 312   case Type::X86_FP80TyID:
 313   case Type::FP128TyID:
 314   case Type::PPC_FP128TyID:
 315     ReplaceCallWith(LDname, CI, CI->op_begin() + 1, CI->op_end(),
 316                   CI->getOperand(1)->getType());
 317     break;
 318   }
 319 }
 320
 321 void IntrinsicLowering::LowerIntrinsicCall(CallInst *CI) {
 322   IRBuilder<> Builder(CI->getParent(), CI);
 323   LLVMContext *Context = CI->getParent()->getContext();
 324
 325   Function *Callee = CI->getCalledFunction();
 326   assert(Callee && "Cannot lower an indirect call!");
 327
 328   switch (Callee->getIntrinsicID()) {
 329   case Intrinsic::not_intrinsic:
 330     llvm_report_error("Cannot lower a call to a non-intrinsic function '"+
 331                       Callee->getName() + "'!");
 332   default:
 333     llvm_report_error("Code generator does not support intrinsic function '"+
 334                       Callee->getName()+"'!");
 335
 336     // The setjmp/longjmp intrinsics should only exist in the code if it was
 337     // never optimized (ie, right out of the CFE), or if it has been hacked on
 338     // by the lowerinvoke pass.  In both cases, the right thing to do is to
 339     // convert the call to an explicit setjmp or longjmp call.
 340   case Intrinsic::setjmp: {
 341     Value *V = ReplaceCallWith("setjmp", CI, CI->op_begin() + 1, CI->op_end(),
 342                                Type::Int32Ty);
 343     if (CI->getType() != Type::VoidTy)
 344       CI->replaceAllUsesWith(V);
 345     break;
 346   }
 347   case Intrinsic::sigsetjmp:
 348      if (CI->getType() != Type::VoidTy)
 349        CI->replaceAllUsesWith(Context->getNullValue(CI->getType()));
 350      break;
 351
 352   case Intrinsic::longjmp: {
 353     ReplaceCallWith("longjmp", CI, CI->op_begin() + 1, CI->op_end(),
 354                     Type::VoidTy);
 355     break;
 356   }
 357
 358   case Intrinsic::siglongjmp: {
 359     // Insert the call to abort
 360     ReplaceCallWith("abort", CI, CI->op_end(), CI->op_end(),
 361                     Type::VoidTy);
 362     break;
 363   }
 364   case Intrinsic::ctpop:
 365     CI->replaceAllUsesWith(LowerCTPOP(*Context, CI->getOperand(1), CI));
 366     break;
 367
 368   case Intrinsic::bswap:
 369     CI->replaceAllUsesWith(LowerBSWAP(*Context, CI->getOperand(1), CI));
 370     break;
 371
 372   case Intrinsic::ctlz:
 373     CI->replaceAllUsesWith(LowerCTLZ(*Context, CI->getOperand(1), CI));
 374     break;
 375
 376   case Intrinsic::cttz: {
 377     // cttz(x) -> ctpop(~X & (X-1))
 378     Value *Src = CI->getOperand(1);
 379     Value *NotSrc = Builder.CreateNot(Src);
 380     NotSrc->setName(Src->getName() + ".not");
 381     Value *SrcM1 = Context->getConstantInt(Src->getType(), 1);
 382     SrcM1 = Builder.CreateSub(Src, SrcM1);
 383     Src = LowerCTPOP(*Context, Builder.CreateAnd(NotSrc, SrcM1), CI);
 384     CI->replaceAllUsesWith(Src);
 385     break;
 386   }
 387
 388   case Intrinsic::stacksave:
 389   case Intrinsic::stackrestore: {
 390     if (!Warned)
 391       cerr << "WARNING: this target does not support the llvm.stack"
 392            << (Callee->getIntrinsicID() == Intrinsic::stacksave ?
 393                "save" : "restore") << " intrinsic.\n";
 394     Warned = true;
 395     if (Callee->getIntrinsicID() == Intrinsic::stacksave)
 396       CI->replaceAllUsesWith(Context->getNullValue(CI->getType()));
 397     break;
 398   }
 399
 400   case Intrinsic::returnaddress:
 401   case Intrinsic::frameaddress:
 402     cerr << "WARNING: this target does not support the llvm."
 403          << (Callee->getIntrinsicID() == Intrinsic::returnaddress ?
 404              "return" : "frame") << "address intrinsic.\n";
 405     CI->replaceAllUsesWith(ConstantPointerNull::get(
 406                                             cast<PointerType>(CI->getType())));
 407     break;
 408
 409   case Intrinsic::prefetch:
 410     break;    // Simply strip out prefetches on unsupported architectures
 411
 412   case Intrinsic::pcmarker:
 413     break;    // Simply strip out pcmarker on unsupported architectures
 414   case Intrinsic::readcyclecounter: {
 415     cerr << "WARNING: this target does not support the llvm.readcyclecoun"
 416          << "ter intrinsic.  It is being lowered to a constant 0\n";
 417     CI->replaceAllUsesWith(Context->getConstantInt(Type::Int64Ty, 0));
 418     break;
 419   }
 420
 421   case Intrinsic::dbg_stoppoint:
 422   case Intrinsic::dbg_region_start:
 423   case Intrinsic::dbg_region_end:
 424   case Intrinsic::dbg_func_start:
 425   case Intrinsic::dbg_declare:
 426     break;    // Simply strip out debugging intrinsics
 427
 428   case Intrinsic::eh_exception:
 429   case Intrinsic::eh_selector_i32:
 430   case Intrinsic::eh_selector_i64:
 431     CI->replaceAllUsesWith(Context->getNullValue(CI->getType()));
 432     break;
 433
 434   case Intrinsic::eh_typeid_for_i32:
 435   case Intrinsic::eh_typeid_for_i64:
 436     // Return something different to eh_selector.
 437     CI->replaceAllUsesWith(Context->getConstantInt(CI->getType(), 1));
 438     break;
 439
 440   case Intrinsic::var_annotation:
 441     break;   // Strip out annotate intrinsic
 442
 443   case Intrinsic::memcpy: {
 444     const IntegerType *IntPtr = TD.getIntPtrType();
 445     Value *Size = Builder.CreateIntCast(CI->getOperand(3), IntPtr,
 446                                         /* isSigned */ false);
 447     Value *Ops[3];
 448     Ops[0] = CI->getOperand(1);
 449     Ops[1] = CI->getOperand(2);
 450     Ops[2] = Size;
 451     ReplaceCallWith("memcpy", CI, Ops, Ops+3, CI->getOperand(1)->getType());
 452     break;
 453   }
 454   case Intrinsic::memmove: {
 455     const IntegerType *IntPtr = TD.getIntPtrType();
 456     Value *Size = Builder.CreateIntCast(CI->getOperand(3), IntPtr,
 457                                         /* isSigned */ false);
 458     Value *Ops[3];
 459     Ops[0] = CI->getOperand(1);
 460     Ops[1] = CI->getOperand(2);
 461     Ops[2] = Size;
 462     ReplaceCallWith("memmove", CI, Ops, Ops+3, CI->getOperand(1)->getType());
 463     break;
 464   }
 465   case Intrinsic::memset: {
 466     const IntegerType *IntPtr = TD.getIntPtrType();
 467     Value *Size = Builder.CreateIntCast(CI->getOperand(3), IntPtr,
 468                                         /* isSigned */ false);
 469     Value *Ops[3];
 470     Ops[0] = CI->getOperand(1);
 471     // Extend the amount to i32.
 472     Ops[1] = Builder.CreateIntCast(CI->getOperand(2), Type::Int32Ty,
 473                                    /* isSigned */ false);
 474     Ops[2] = Size;
 475     ReplaceCallWith("memset", CI, Ops, Ops+3, CI->getOperand(1)->getType());
 476     break;
 477   }
 478   case Intrinsic::sqrt: {
 479     ReplaceFPIntrinsicWithCall(CI, "sqrtf", "sqrt", "sqrtl");
 480     break;
 481   }
 482   case Intrinsic::log: {
 483     ReplaceFPIntrinsicWithCall(CI, "logf", "log", "logl");
 484     break;
 485   }
 486   case Intrinsic::log2: {
 487     ReplaceFPIntrinsicWithCall(CI, "log2f", "log2", "log2l");
 488     break;
 489   }
 490   case Intrinsic::log10: {
 491     ReplaceFPIntrinsicWithCall(CI, "log10f", "log10", "log10l");
 492     break;
 493   }
 494   case Intrinsic::exp: {
 495     ReplaceFPIntrinsicWithCall(CI, "expf", "exp", "expl");
 496     break;
 497   }
 498   case Intrinsic::exp2: {
 499     ReplaceFPIntrinsicWithCall(CI, "exp2f", "exp2", "exp2l");
 500     break;
 501   }
 502   case Intrinsic::pow: {
 503     ReplaceFPIntrinsicWithCall(CI, "powf", "pow", "powl");
 504     break;
 505   }
 506   case Intrinsic::flt_rounds:
 507      // Lower to "round to the nearest"
 508      if (CI->getType() != Type::VoidTy)
 509        CI->replaceAllUsesWith(Context->getConstantInt(CI->getType(), 1));
 510      break;
 511   }
 512
 513   assert(CI->use_empty() &&
 514          "Lowering should have eliminated any uses of the intrinsic call!");
 515   CI->eraseFromParent();
 516 }