SimplifyLibCalls.cpp

//===- SimplifyLibCalls.cpp - Optimize specific well-known library calls --===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements a simple pass that applies a variety of small
// optimizations for calls to specific well-known function calls (e.g. runtime
// library functions). For example, a call to the function "exit(3)" that
// occurs within the main() function can be transformed into a simple "return 3"
// instruction. Any optimization that takes this form (replace call to library
// function with simpler code that provides the same result) belongs in this
// file.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "simplify-libcalls"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Intrinsics.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "llvm/Support/IRBuilder.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Target/TargetData.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Config/config.h"
using namespace llvm;

STATISTIC(NumSimplified, "Number of library calls simplified");
STATISTIC(NumAnnotated, "Number of attributes added to library functions");

//===----------------------------------------------------------------------===//
// Optimizer Base Class
//===----------------------------------------------------------------------===//

/// This class is the abstract base class for the set of optimizations that
/// corresponds to one library call.
namespace {
class VISIBILITY_HIDDEN LibCallOptimization {
protected:
  Function *Caller;
  const TargetData *TD;
public:
  LibCallOptimization() { }
  virtual ~LibCallOptimization() {}

  /// CallOptimizer - This pure virtual method is implemented by base classes to
  /// do various optimizations.  If this returns null then no transformation was
  /// performed.  If it returns CI, then it transformed the call and CI is to be
  /// deleted.  If it returns something else, replace CI with the new value and
  /// delete CI.
  virtual Value *CallOptimizer(Function *Callee, CallInst *CI, IRBuilder<> &B) 
    =0;
  
  Value *OptimizeCall(CallInst *CI, const TargetData &TD, IRBuilder<> &B) {
    Caller = CI->getParent()->getParent();
    this->TD = &TD;
    return CallOptimizer(CI->getCalledFunction(), CI, B);
  }

  /// CastToCStr - Return V if it is an i8*, otherwise cast it to i8*.
  Value *CastToCStr(Value *V, IRBuilder<> &B);

  /// EmitStrLen - Emit a call to the strlen function to the builder, for the
  /// specified pointer.  Ptr is required to be some pointer type, and the
  /// return value has 'intptr_t' type.
  Value *EmitStrLen(Value *Ptr, IRBuilder<> &B);
  
  /// EmitMemCpy - Emit a call to the memcpy function to the builder.  This
  /// always expects that the size has type 'intptr_t' and Dst/Src are pointers.
  Value *EmitMemCpy(Value *Dst, Value *Src, Value *Len, 
                    unsigned Align, IRBuilder<> &B);
  
  /// EmitMemChr - Emit a call to the memchr function.  This assumes that Ptr is
  /// a pointer, Val is an i32 value, and Len is an 'intptr_t' value.
  Value *EmitMemChr(Value *Ptr, Value *Val, Value *Len, IRBuilder<> &B);

  /// EmitMemCmp - Emit a call to the memcmp function.
  Value *EmitMemCmp(Value *Ptr1, Value *Ptr2, Value *Len, IRBuilder<> &B);

  /// EmitUnaryFloatFnCall - Emit a call to the unary function named 'Name' (e.g.
  /// 'floor').  This function is known to take a single of type matching 'Op'
  /// and returns one value with the same type.  If 'Op' is a long double, 'l'
  /// is added as the suffix of name, if 'Op' is a float, we add a 'f' suffix.
  Value *EmitUnaryFloatFnCall(Value *Op, const char *Name, IRBuilder<> &B);
  
  /// EmitPutChar - Emit a call to the putchar function.  This assumes that Char
  /// is an integer.
  void EmitPutChar(Value *Char, IRBuilder<> &B);
  
  /// EmitPutS - Emit a call to the puts function.  This assumes that Str is
  /// some pointer.
  void EmitPutS(Value *Str, IRBuilder<> &B);
    
  /// EmitFPutC - Emit a call to the fputc function.  This assumes that Char is
  /// an i32, and File is a pointer to FILE.
  void EmitFPutC(Value *Char, Value *File, IRBuilder<> &B);
  
  /// EmitFPutS - Emit a call to the puts function.  Str is required to be a
  /// pointer and File is a pointer to FILE.
  void EmitFPutS(Value *Str, Value *File, IRBuilder<> &B);
  
  /// EmitFWrite - Emit a call to the fwrite function.  This assumes that Ptr is
  /// a pointer, Size is an 'intptr_t', and File is a pointer to FILE.
  void EmitFWrite(Value *Ptr, Value *Size, Value *File, IRBuilder<> &B);
  
};
} // End anonymous namespace.

/// CastToCStr - Return V if it is an i8*, otherwise cast it to i8*.
Value *LibCallOptimization::CastToCStr(Value *V, IRBuilder<> &B) {
  return B.CreateBitCast(V, PointerType::getUnqual(Type::Int8Ty), "cstr");
}

/// EmitStrLen - Emit a call to the strlen function to the builder, for the
/// specified pointer.  This always returns an integer value of size intptr_t.
Value *LibCallOptimization::EmitStrLen(Value *Ptr, IRBuilder<> &B) {
  Module *M = Caller->getParent();
  AttributeWithIndex AWI[2];
  AWI[0] = AttributeWithIndex::get(1, Attribute::NoCapture);
  AWI[1] = AttributeWithIndex::get(~0u, Attribute::ReadOnly |
                                   Attribute::NoUnwind);

  Constant *StrLen =M->getOrInsertFunction("strlen", AttrListPtr::get(AWI, 2),
                                           TD->getIntPtrType(),
                                           PointerType::getUnqual(Type::Int8Ty),
                                           NULL);
  return B.CreateCall(StrLen, CastToCStr(Ptr, B), "strlen");
}

/// EmitMemCpy - Emit a call to the memcpy function to the builder.  This always
/// expects that the size has type 'intptr_t' and Dst/Src are pointers.
Value *LibCallOptimization::EmitMemCpy(Value *Dst, Value *Src, Value *Len,
                                       unsigned Align, IRBuilder<> &B) {
  Module *M = Caller->getParent();
  Intrinsic::ID IID = Intrinsic::memcpy;
  const Type *Tys[1];
  Tys[0] = Len->getType();
  Value *MemCpy = Intrinsic::getDeclaration(M, IID, Tys, 1);
  return B.CreateCall4(MemCpy, CastToCStr(Dst, B), CastToCStr(Src, B), Len,
                       ConstantInt::get(Type::Int32Ty, Align));
}

/// EmitMemChr - Emit a call to the memchr function.  This assumes that Ptr is
/// a pointer, Val is an i32 value, and Len is an 'intptr_t' value.
Value *LibCallOptimization::EmitMemChr(Value *Ptr, Value *Val,
                                       Value *Len, IRBuilder<> &B) {
  Module *M = Caller->getParent();
  AttributeWithIndex AWI;
  AWI = AttributeWithIndex::get(~0u, Attribute::ReadOnly | Attribute::NoUnwind);

  Value *MemChr = M->getOrInsertFunction("memchr", AttrListPtr::get(&AWI, 1),
                                         PointerType::getUnqual(Type::Int8Ty),
                                         PointerType::getUnqual(Type::Int8Ty),
                                         Type::Int32Ty, TD->getIntPtrType(),
                                         NULL);
  return B.CreateCall3(MemChr, CastToCStr(Ptr, B), Val, Len, "memchr");
}

/// EmitMemCmp - Emit a call to the memcmp function.
Value *LibCallOptimization::EmitMemCmp(Value *Ptr1, Value *Ptr2,
                                       Value *Len, IRBuilder<> &B) {
  Module *M = Caller->getParent();
  AttributeWithIndex AWI[3];
  AWI[0] = AttributeWithIndex::get(1, Attribute::NoCapture);
  AWI[1] = AttributeWithIndex::get(2, Attribute::NoCapture);
  AWI[2] = AttributeWithIndex::get(~0u, Attribute::ReadOnly |
                                   Attribute::NoUnwind);

  Value *MemCmp = M->getOrInsertFunction("memcmp", AttrListPtr::get(AWI, 3),
                                         Type::Int32Ty,
                                         PointerType::getUnqual(Type::Int8Ty),
                                         PointerType::getUnqual(Type::Int8Ty),
                                         TD->getIntPtrType(), NULL);
  return B.CreateCall3(MemCmp, CastToCStr(Ptr1, B), CastToCStr(Ptr2, B),
                       Len, "memcmp");
}

/// EmitUnaryFloatFnCall - Emit a call to the unary function named 'Name' (e.g.
/// 'floor').  This function is known to take a single of type matching 'Op' and
/// returns one value with the same type.  If 'Op' is a long double, 'l' is
/// added as the suffix of name, if 'Op' is a float, we add a 'f' suffix.
Value *LibCallOptimization::EmitUnaryFloatFnCall(Value *Op, const char *Name,
                                                 IRBuilder<> &B) {
  char NameBuffer[20];
  if (Op->getType() != Type::DoubleTy) {
    // If we need to add a suffix, copy into NameBuffer.
    unsigned NameLen = strlen(Name);
    assert(NameLen < sizeof(NameBuffer)-2);
    memcpy(NameBuffer, Name, NameLen);
    if (Op->getType() == Type::FloatTy)
      NameBuffer[NameLen] = 'f';  // floorf
    else