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).   Any optimization that takes the very simple 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/LLVMContext.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/ADT/STLExtras.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.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 LibCallOptimization {
protected:
  Function *Caller;
  const TargetData *TD;
  LLVMContext* Context;
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;
    if (CI->getCalledFunction())
      Context = &CI->getCalledFunction()->getContext();
    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);

  /// EmitStrChr - Emit a call to the strchr function to the builder, for the
  /// specified pointer and character.  Ptr is required to be some pointer type,
  /// and the return value has 'i8*' type.
  Value *EmitStrChr(Value *Ptr, char C, IRBuilder<> &B);

  /// EmitStrCpy - Emit a call to the strcpy function to the builder, for the
  /// specified pointer arguments.
  Value *EmitStrCpy(Value *Dst, Value *Src, 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);

  /// EmitMemMove - Emit a call to the memmove function to the builder.  This
  /// always expects that the size has type 'intptr_t' and Dst/Src are pointers.
  Value *EmitMemMove(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);

  /// EmitMemSet - Emit a call to the memset function
  Value *EmitMemSet(Value *Dst, Value *Val, 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,
                              const AttrListPtr &Attrs);

  /// EmitPutChar - Emit a call to the putchar function.  This assumes that Char
  /// is an integer.
  Value *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, Type::getInt8PtrTy(*Context), "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(*Context),
                                           Type::getInt8PtrTy(*Context),
                                           NULL);
  CallInst *CI = B.CreateCall(StrLen, CastToCStr(Ptr, B), "strlen");
  if (const Function *F = dyn_cast<Function>(StrLen->stripPointerCasts()))
    CI->setCallingConv(F->getCallingConv());

  return CI;
}

/// EmitStrChr - Emit a call to the strchr function to the builder, for the
/// specified pointer and character.  Ptr is required to be some pointer type,
/// and the return value has 'i8*' type.
Value *LibCallOptimization::EmitStrChr(Value *Ptr, char C, IRBuilder<> &B) {
  Module *M = Caller->getParent();
  AttributeWithIndex AWI =
    AttributeWithIndex::get(~0u, Attribute::ReadOnly | Attribute::NoUnwind);

  const Type *I8Ptr = Type::getInt8PtrTy(*Context);
  const Type *I32Ty = Type::getInt32Ty(*Context);
  Constant *StrChr = M->getOrInsertFunction("strchr", AttrListPtr::get(&AWI, 1),
                                            I8Ptr, I8Ptr, I32Ty, NULL);
  CallInst *CI = B.CreateCall2(StrChr, CastToCStr(Ptr, B),
                               ConstantInt::get(I32Ty, C), "strchr");
  if (const Function *F = dyn_cast<Function>(StrChr->stripPointerCasts()))
    CI->setCallingConv(F->getCallingConv());
  return CI;
}

/// EmitStrCpy - Emit a call to the strcpy function to the builder, for the
/// specified pointer arguments.
Value *LibCallOptimization::EmitStrCpy(Value *Dst, Value *Src, IRBuilder<> &B) {
  Module *M = Caller->getParent();
  AttributeWithIndex AWI[2];
  AWI[0] = AttributeWithIndex::get(2, Attribute::NoCapture);
  AWI[1] = AttributeWithIndex::get(~0u, Attribute::NoUnwind);
  const Type *I8Ptr = Type::getInt8PtrTy(*Context);
  Value *StrCpy = M->getOrInsertFunction("strcpy", AttrListPtr::get(AWI, 2),
                                         I8Ptr, I8Ptr, I8Ptr, NULL);
  CallInst *CI = B.CreateCall2(StrCpy, CastToCStr(Dst, B), CastToCStr(Src, B),
                               "strcpy");
  if (const Function *F = dyn_cast<Function>(StrCpy->stripPointerCasts()))
    CI->setCallingConv(F->getCallingConv());
  return CI;
}

/// EmitMemCpy - Emit a call to the memcpy function to the builder.  This always