OSchip
/
llvm-project
mirror of https://github.com/THU-DSP-LAB/llvm-project.git
13
0
Fork 6
Code Issues Packages Projects Releases Wiki Activity
llvm-project/llvm/lib/Transforms/IPO/SimplifyLibCalls.cpp

747 lines
28 KiB
C++
Raw Blame History

//===- SimplifyLibCalls.cpp - Optimize specific well-known library calls --===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by Reid Spencer and is distributed under the
// University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements a variety of small optimizations for calls to specific
// well-known (e.g. runtime library) function calls. 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 same
// result) belongs in this file.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "simplify-libcalls"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Instructions.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "llvm/ADT/hash_map"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/Debug.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Transforms/IPO.h"
#include <iostream>
using namespace llvm;
namespace {
/// This statistic keeps track of the total number of library calls that have
/// been simplified regardless of which call it is.
Statistic<> SimplifiedLibCalls("simplify-libcalls",
"Number of well-known library calls simplified");
// Forward declarations
class LibCallOptimization;
class SimplifyLibCalls;
/// @brief The list of optimizations deriving from LibCallOptimization
hash_map<std::string,LibCallOptimization*> optlist;
/// This class is the abstract base class for the set of optimizations that
/// corresponds to one library call. The SimplifyLibCalls pass will call the
/// ValidateCalledFunction method to ask the optimization if a given Function
/// is the kind that the optimization can handle. If the subclass returns true,
/// then SImplifyLibCalls will also call the OptimizeCall method to perform,
/// or attempt to perform, the optimization(s) for the library call. Otherwise,
/// OptimizeCall won't be called. Subclasses are responsible for providing the
/// name of the library call (strlen, strcpy, etc.) to the LibCallOptimization
/// constructor. This is used to efficiently select which call instructions to
/// optimize. The criteria for a "lib call" is "anything with well known
/// semantics", typically a library function that is defined by an international
/// standard. Because the semantics are well known, the optimizations can
/// generally short-circuit actually calling the function if there's a simpler
/// way (e.g. strlen(X) can be reduced to a constant if X is a constant global).
/// @brief Base class for library call optimizations
struct LibCallOptimization
{
/// The \p fname argument must be the name of the library function being
/// optimized by the subclass.
/// @brief Constructor that registers the optimization.
LibCallOptimization(const char * fname )
: func_name(fname)
#ifndef NDEBUG
, stat_name(std::string("simplify-libcalls:")+fname)
, occurrences(stat_name.c_str(),"Number of calls simplified")
#endif
{
// Register this call optimizer in the optlist (a hash_map)
optlist[func_name] = this;
}
/// @brief Deregister from the optlist
virtual ~LibCallOptimization() { optlist.erase(func_name); }
/// The implementation of this function in subclasses should determine if
/// \p F is suitable for the optimization. This method is called by
/// SimplifyLibCalls::runOnModule to short circuit visiting all the call
/// sites of such a function if that function is not suitable in the first
/// place. If the called function is suitabe, this method should return true;
/// false, otherwise. This function should also perform any lazy
/// initialization that the LibCallOptimization needs to do, if its to return
/// true. This avoids doing initialization until the optimizer is actually
/// going to be called upon to do some optimization.
/// @brief Determine if the function is suitable for optimization
virtual bool ValidateCalledFunction(
const Function* F, ///< The function that is the target of call sites
SimplifyLibCalls& SLC ///< The pass object invoking us
) = 0;
/// The implementations of this function in subclasses is the heart of the
/// SimplifyLibCalls algorithm. Sublcasses of this class implement
/// OptimizeCall to determine if (a) the conditions are right for optimizing
/// the call and (b) to perform the optimization. If an action is taken
/// against ci, the subclass is responsible for returning true and ensuring
/// that ci is erased from its parent.
/// @brief Optimize a call, if possible.
virtual bool OptimizeCall(
CallInst* ci, ///< The call instruction that should be optimized.
SimplifyLibCalls& SLC ///< The pass object invoking us
) = 0;
/// @brief Get the name of the library call being optimized
const char * getFunctionName() const { return func_name; }
#ifndef NDEBUG
/// @brief Called by SimplifyLibCalls to update the occurrences statistic.
void succeeded() { ++occurrences; }
#endif
private:
const char* func_name; ///< Name of the library call we optimize
#ifndef NDEBUG
std::string stat_name; ///< Holder for debug statistic name
Statistic<> occurrences; ///< debug statistic (-debug-only=simplify-libcalls)
#endif
};
/// This class is an LLVM Pass that applies each of the LibCallOptimization
/// instances to all the call sites in a module, relatively efficiently. The
/// purpose of this pass is to provide optimizations for calls to well-known
/// functions with well-known semantics, such as those in the c library. The
/// class provides the basic infrastructure for handling runOnModule. Whenever /// this pass finds a function call, it asks the appropriate optimizer to
/// validate the call (ValidateLibraryCall). If it is validated, then
/// the OptimizeCall method is also called.
/// @brief A ModulePass for optimizing well-known function calls.
struct SimplifyLibCalls : public ModulePass
{
/// We need some target data for accurate signature details that are
/// target dependent. So we require target data in our AnalysisUsage.
/// @brief Require TargetData from AnalysisUsage.
virtual void getAnalysisUsage(AnalysisUsage& Info) const
{
// Ask that the TargetData analysis be performed before us so we can use
// the target data.
Info.addRequired<TargetData>();
}
/// For this pass, process all of the function calls in the module, calling
/// ValidateLibraryCall and OptimizeCall as appropriate.
/// @brief Run all the lib call optimizations on a Module.
virtual bool runOnModule(Module &M)
{
reset(M);
bool result = false;
// The call optimizations can be recursive. That is, the optimization might
// generate a call to another function which can also be optimized. This way
// we make the LibCallOptimization instances very specific to the case they
// handle. It also means we need to keep running over the function calls in
// the module until we don't get any more optimizations possible.
bool found_optimization = false;
do
{
found_optimization = false;
for (Module::iterator FI = M.begin(), FE = M.end(); FI != FE; ++FI)
{
// All the "well-known" functions are external and have external linkage
// because they live in a runtime library somewhere and were (probably)
// not compiled by LLVM. So, we only act on external functions that have
// external linkage and non-empty uses.
if (!FI->isExternal() || !FI->hasExternalLinkage() || FI->use_empty())
continue;
// Get the optimization class that pertains to this function
LibCallOptimization* CO = optlist[FI->getName().c_str()];
if (!CO)
continue;
// Make sure the called function is suitable for the optimization
if (!CO->ValidateCalledFunction(FI,*this))
continue;
// Loop over each of the uses of the function
for (Value::use_iterator UI = FI->use_begin(), UE = FI->use_end();
UI != UE ; )
{
// If the use of the function is a call instruction
if (CallInst* CI = dyn_cast<CallInst>(*UI++))
{
// Do the optimization on the LibCallOptimization.
if (CO->OptimizeCall(CI,*this))
{
++SimplifiedLibCalls;
found_optimization = result = true;
#ifndef NDEBUG
CO->succeeded();
#endif
}
}
}
}
} while (found_optimization);
return result;
}
/// @brief Return the *current* module we're working on.
Module* getModule() { return M; }
/// @brief Return the *current* target data for the module we're working on.
TargetData* getTargetData() { return TD; }
/// @brief Return a Function* for the strlen libcall
Function* get_strlen()
{
if (!strlen_func)
{
std::vector<const Type*> args;
args.push_back(PointerType::get(Type::SByteTy));
FunctionType* strlen_type =
FunctionType::get(TD->getIntPtrType(), args, false);
strlen_func = M->getOrInsertFunction("strlen",strlen_type);
}
return strlen_func;
}
/// @brief Return a Function* for the memcpy libcall
Function* get_memcpy()
{
if (!memcpy_func)
{
// Note: this is for llvm.memcpy intrinsic
std::vector<const Type*> args;
args.push_back(PointerType::get(Type::SByteTy));
args.push_back(PointerType::get(Type::SByteTy));
args.push_back(Type::IntTy);
args.push_back(Type::IntTy);
FunctionType* memcpy_type = FunctionType::get(Type::VoidTy, args, false);
memcpy_func = M->getOrInsertFunction("llvm.memcpy",memcpy_type);
}
return memcpy_func;
}
private:
/// @brief Reset our cached data for a new Module
void reset(Module& mod)
{
M = &mod;
TD = &getAnalysis<TargetData>();
memcpy_func = 0;
strlen_func = 0;
}
private:
Function* memcpy_func; ///< Cached llvm.memcpy function
Function* strlen_func; ///< Cached strlen function
Module* M; ///< Cached Module
TargetData* TD; ///< Cached TargetData
};
// Register the pass
RegisterOpt<SimplifyLibCalls>
X("simplify-libcalls","Simplify well-known library calls");
} // anonymous namespace
// The only public symbol in this file which just instantiates the pass object
ModulePass *llvm::createSimplifyLibCallsPass()
{
return new SimplifyLibCalls();
}
// Classes below here, in the anonymous namespace, are all subclasses of the
// LibCallOptimization class, each implementing all optimizations possible for a
// single well-known library call. Each has a static singleton instance that
// auto registers it into the "optlist" global above.
namespace {
// Forward declare a utility function.
bool getConstantStringLength(Value* V, uint64_t& len );
/// This LibCallOptimization will find instances of a call to "exit" that occurs
/// within the "main" function and change it to a simple "ret" instruction with
/// the same value passed to the exit function. When this is done, it splits the
/// basic block at the exit(3) call and deletes the call instruction.
/// @brief Replace calls to exit in main with a simple return
struct ExitInMainOptimization : public LibCallOptimization
{
ExitInMainOptimization() : LibCallOptimization("exit") {}
virtual ~ExitInMainOptimization() {}
// Make sure the called function looks like exit (int argument, int return
// type, external linkage, not varargs).
virtual bool ValidateCalledFunction(const Function* f, SimplifyLibCalls& SLC)
{
if (f->arg_size() >= 1)
if (f->arg_begin()->getType()->isInteger())
return true;
return false;
}
virtual bool OptimizeCall(CallInst* ci, SimplifyLibCalls& SLC)
{
// To be careful, we check that the call to exit is coming from "main", that
// main has external linkage, and the return type of main and the argument
// to exit have the same type.
Function *from = ci->getParent()->getParent();
if (from->hasExternalLinkage())
if (from->getReturnType() == ci->getOperand(1)->getType())
if (from->getName() == "main")
{
// Okay, time to actually do the optimization. First, get the basic
// block of the call instruction
BasicBlock* bb = ci->getParent();
// Create a return instruction that we'll replace the call with.
// Note that the argument of the return is the argument of the call
// instruction.
ReturnInst* ri = new ReturnInst(ci->getOperand(1), ci);
// Split the block at the call instruction which places it in a new
// basic block.
bb->splitBasicBlock(ci);
// The block split caused a branch instruction to be inserted into
// the end of the original block, right after the return instruction
// that we put there. That's not a valid block, so delete the branch
// instruction.
bb->getInstList().pop_back();
// Now we can finally get rid of the call instruction which now lives
// in the new basic block.
ci->eraseFromParent();
// Optimization succeeded, return true.
return true;
}
// We didn't pass the criteria for this optimization so return false
return false;
}
} ExitInMainOptimizer;
/// This LibCallOptimization will simplify a call to the strcat library
/// function. The simplification is possible only if the string being
/// concatenated is a constant array or a constant expression that results in
/// a constant string. In this case we can replace it with strlen + llvm.memcpy
/// of the constant string. Both of these calls are further reduced, if possible
/// on subsequent passes.
/// @brief Simplify the strcat library function.
struct StrCatOptimization : public LibCallOptimization
{
public:
/// @brief Default constructor
StrCatOptimization() : LibCallOptimization("strcat") {}
public:
/// @breif Destructor
virtual ~StrCatOptimization() {}
/// @brief Make sure that the "strcat" function has the right prototype
virtual bool ValidateCalledFunction(const Function* f, SimplifyLibCalls& SLC)
{
if (f->getReturnType() == PointerType::get(Type::SByteTy))
if (f->arg_size() == 2)
{
Function::const_arg_iterator AI = f->arg_begin();
if (AI++->getType() == PointerType::get(Type::SByteTy))
if (AI->getType() == PointerType::get(Type::SByteTy))
{
// Indicate this is a suitable call type.
return true;
}
}
return false;
}
/// @brief Optimize the strcat library function
virtual bool OptimizeCall(CallInst* ci, SimplifyLibCalls& SLC)
{
// Extract some information from the instruction
Module* M = ci->getParent()->getParent()->getParent();
Value* dest = ci->getOperand(1);
Value* src = ci->getOperand(2);
// Extract the initializer (while making numerous checks) from the
// source operand of the call to strcat. If we get null back, one of
// a variety of checks in get_GVInitializer failed
uint64_t len = 0;
if (!getConstantStringLength(src,len))
return false;
// Handle the simple, do-nothing case
if (len == 0)
{
ci->replaceAllUsesWith(dest);
ci->eraseFromParent();
return true;
}
// Increment the length because we actually want to memcpy the null
// terminator as well.
len++;
// We need to find the end of the destination string. That's where the
// memory is to be moved to. We just generate a call to strlen (further
// optimized in another pass). Note that the SLC.get_strlen() call
// caches the Function* for us.
CallInst* strlen_inst =
new CallInst(SLC.get_strlen(), dest, dest->getName()+".len",ci);
// Now that we have the destination's length, we must index into the
// destination's pointer to get the actual memcpy destination (end of
// the string .. we're concatenating).
std::vector<Value*> idx;
idx.push_back(strlen_inst);
GetElementPtrInst* gep =
new GetElementPtrInst(dest,idx,dest->getName()+".indexed",ci);
// We have enough information to now generate the memcpy call to
// do the concatenation for us.
std::vector<Value*> vals;
vals.push_back(gep); // destination
vals.push_back(ci->getOperand(2)); // source
vals.push_back(ConstantSInt::get(Type::IntTy,len)); // length
vals.push_back(ConstantSInt::get(Type::IntTy,1)); // alignment
new CallInst(SLC.get_memcpy(), vals, "", ci);
// Finally, substitute the first operand of the strcat call for the
// strcat call itself since strcat returns its first operand; and,
// kill the strcat CallInst.
ci->replaceAllUsesWith(dest);
ci->eraseFromParent();
return true;
}
} StrCatOptimizer;
/// This LibCallOptimization will simplify a call to the strcpy library
/// function. Two optimizations are possible:
/// (1) If src and dest are the same and not volatile, just return dest
/// (2) If the src is a constant then we can convert to llvm.memmove
/// @brief Simplify the strcpy library function.
struct StrCpyOptimization : public LibCallOptimization
{
public:
StrCpyOptimization() : LibCallOptimization("strcpy") {}
virtual ~StrCpyOptimization() {}
/// @brief Make sure that the "strcpy" function has the right prototype
virtual bool ValidateCalledFunction(const Function* f, SimplifyLibCalls& SLC)
{
if (f->getReturnType() == PointerType::get(Type::SByteTy))
if (f->arg_size() == 2)
{
Function::const_arg_iterator AI = f->arg_begin();
if (AI++->getType() == PointerType::get(Type::SByteTy))
if (AI->getType() == PointerType::get(Type::SByteTy))
{
// Indicate this is a suitable call type.
return true;
}
}
return false;
}
/// @brief Perform the strcpy optimization
virtual bool OptimizeCall(CallInst* ci, SimplifyLibCalls& SLC)
{
// First, check to see if src and destination are the same. If they are,
// then the optimization is to replace the CallInst with the destination
// because the call is a no-op. Note that this corresponds to the
// degenerate strcpy(X,X) case which should have "undefined" results
// according to the C specification. However, it occurs sometimes and
// we optimize it as a no-op.
Value* dest = ci->getOperand(1);
Value* src = ci->getOperand(2);
if (dest == src)
{
ci->replaceAllUsesWith(dest);
ci->eraseFromParent();
return true;
}
// Get the length of the constant string referenced by the second operand,
// the "src" parameter. Fail the optimization if we can't get the length
// (note that getConstantStringLength does lots of checks to make sure this
// is valid).
uint64_t len = 0;
if (!getConstantStringLength(ci->getOperand(2),len))
return false;
// If the constant string's length is zero we can optimize this by just
// doing a store of 0 at the first byte of the destination
if (len == 0)
{
new StoreInst(ConstantInt::get(Type::SByteTy,0),ci->getOperand(1),ci);
ci->replaceAllUsesWith(dest);
ci->eraseFromParent();
return true;
}
// Increment the length because we actually want to memcpy the null
// terminator as well.
len++;
// Extract some information from the instruction
Module* M = ci->getParent()->getParent()->getParent();
// We have enough information to now generate the memcpy call to
// do the concatenation for us.
std::vector<Value*> vals;
vals.push_back(dest); // destination
vals.push_back(src); // source
vals.push_back(ConstantSInt::get(Type::IntTy,len)); // length
vals.push_back(ConstantSInt::get(Type::IntTy,1)); // alignment
new CallInst(SLC.get_memcpy(), vals, "", ci);
// Finally, substitute the first operand of the strcat call for the
// strcat call itself since strcat returns its first operand; and,
// kill the strcat CallInst.
ci->replaceAllUsesWith(dest);
ci->eraseFromParent();
return true;
}
} StrCpyOptimizer;
/// This LibCallOptimization will simplify a call to the strlen library
/// function by replacing it with a constant value if the string provided to
/// it is a constant array.
/// @brief Simplify the strlen library function.
struct StrLenOptimization : public LibCallOptimization
{
StrLenOptimization() : LibCallOptimization("strlen") {}
virtual ~StrLenOptimization() {}
/// @brief Make sure that the "strlen" function has the right prototype
virtual bool ValidateCalledFunction(const Function* f, SimplifyLibCalls& SLC)
{
if (f->getReturnType() == SLC.getTargetData()->getIntPtrType())
if (f->arg_size() == 1)
if (Function::const_arg_iterator AI = f->arg_begin())
if (AI->getType() == PointerType::get(Type::SByteTy))
return true;
return false;
}
/// @brief Perform the strlen optimization
virtual bool OptimizeCall(CallInst* ci, SimplifyLibCalls& SLC)
{
// Get the length of the string
uint64_t len = 0;
if (!getConstantStringLength(ci->getOperand(1),len))
return false;
ci->replaceAllUsesWith(
ConstantInt::get(SLC.getTargetData()->getIntPtrType(),len));
ci->eraseFromParent();
return true;
}
} StrLenOptimizer;
/// This LibCallOptimization will simplify a call to the memcpy library
/// function by expanding it out to a single store of size 0, 1, 2, 4, or 8
/// bytes depending on the length of the string and the alignment. Additional
/// optimizations are possible in code generation (sequence of immediate store)
/// @brief Simplify the memcpy library function.
struct MemCpyOptimization : public LibCallOptimization
{
/// @brief Default Constructor
MemCpyOptimization() : LibCallOptimization("llvm.memcpy") {}
protected:
/// @brief Subclass Constructor
MemCpyOptimization(const char* fname) : LibCallOptimization(fname) {}
public:
/// @brief Destructor
virtual ~MemCpyOptimization() {}
/// @brief Make sure that the "memcpy" function has the right prototype
virtual bool ValidateCalledFunction(const Function* f, SimplifyLibCalls& TD)
{
// Just make sure this has 4 arguments per LLVM spec.
return (f->arg_size() == 4);
}
/// Because of alignment and instruction information that we don't have, we
/// leave the bulk of this to the code generators. The optimization here just
/// deals with a few degenerate cases where the length of the string and the
/// alignment match the sizes of our intrinsic types so we can do a load and
/// store instead of the memcpy call.
/// @brief Perform the memcpy optimization.
virtual bool OptimizeCall(CallInst* ci, SimplifyLibCalls& TD)
{
// Make sure we have constant int values to work with
ConstantInt* LEN = dyn_cast<ConstantInt>(ci->getOperand(3));
if (!LEN)
return false;
ConstantInt* ALIGN = dyn_cast<ConstantInt>(ci->getOperand(4));
if (!ALIGN)
return false;
// If the length is larger than the alignment, we can't optimize
uint64_t len = LEN->getRawValue();
uint64_t alignment = ALIGN->getRawValue();
if (len > alignment)
return false;
// Get the type we will cast to, based on size of the string
Value* dest = ci->getOperand(1);
Value* src = ci->getOperand(2);
Type* castType = 0;
switch (len)
{
case 0:
// The memcpy is a no-op so just dump its call.
ci->eraseFromParent();
return true;
case 1: castType = Type::SByteTy; break;
case 2: castType = Type::ShortTy; break;
case 4: castType = Type::IntTy; break;
case 8: castType = Type::LongTy; break;
default:
return false;
}
// Cast source and dest to the right sized primitive and then load/store
CastInst* SrcCast =
new CastInst(src,PointerType::get(castType),src->getName()+".cast",ci);
CastInst* DestCast =
new CastInst(dest,PointerType::get(castType),dest->getName()+".cast",ci);
LoadInst* LI = new LoadInst(SrcCast,SrcCast->getName()+".val",ci);
StoreInst* SI = new StoreInst(LI, DestCast, ci);
ci->eraseFromParent();
return true;
}
} MemCpyOptimizer;
/// This LibCallOptimization will simplify a call to the memmove library
/// function. It is identical to MemCopyOptimization except for the name of
/// the intrinsic.
/// @brief Simplify the memmove library function.
struct MemMoveOptimization : public MemCpyOptimization
{
/// @brief Default Constructor
MemMoveOptimization() : MemCpyOptimization("llvm.memmove") {}
} MemMoveOptimizer;
/// A function to compute the length of a null-terminated constant array of
/// integers. This function can't rely on the size of the constant array
/// because there could be a null terminator in the middle of the array.
/// We also have to bail out if we find a non-integer constant initializer
/// of one of the elements or if there is no null-terminator. The logic
/// below checks each of these conditions and will return true only if all
/// conditions are met. In that case, the \p len parameter is set to the length
/// of the null-terminated string. If false is returned, the conditions were
/// not met and len is set to 0.
/// @brief Get the length of a constant string (null-terminated array).
bool getConstantStringLength(Value* V, uint64_t& len )
{
assert(V != 0 && "Invalid args to getConstantStringLength");
len = 0; // make sure we initialize this
User* GEP = 0;
// If the value is not a GEP instruction nor a constant expression with a
// GEP instruction, then return false because ConstantArray can't occur
// any other way
if (GetElementPtrInst* GEPI = dyn_cast<GetElementPtrInst>(V))
GEP = GEPI;
else if (ConstantExpr* CE = dyn_cast<ConstantExpr>(V))
if (CE->getOpcode() == Instruction::GetElementPtr)
GEP = CE;
else
return false;
else
return false;
// Make sure the GEP has exactly three arguments.
if (GEP->getNumOperands() != 3)
return false;
// Check to make sure that the first operand of the GEP is an integer and
// has value 0 so that we are sure we're indexing into the initializer.
if (ConstantInt* op1 = dyn_cast<ConstantInt>(GEP->getOperand(1)))
{
if (!op1->isNullValue())
return false;
}
else
return false;
// Ensure that the second operand is a ConstantInt. If it isn't then this
// GEP is wonky and we're not really sure what were referencing into and
// better of not optimizing it. While we're at it, get the second index
// value. We'll need this later for indexing the ConstantArray.
uint64_t start_idx = 0;
if (ConstantInt* CI = dyn_cast<ConstantInt>(GEP->getOperand(2)))
start_idx = CI->getRawValue();
else
return false;
// The GEP instruction, constant or instruction, must reference a global
// variable that is a constant and is initialized. The referenced constant
// initializer is the array that we'll use for optimization.
GlobalVariable* GV = dyn_cast<GlobalVariable>(GEP->getOperand(0));
if (!GV || !GV->isConstant() || !GV->hasInitializer())
return false;
// Get the initializer.
Constant* INTLZR = GV->getInitializer();
// Handle the ConstantAggregateZero case
if (ConstantAggregateZero* CAZ = dyn_cast<ConstantAggregateZero>(INTLZR))
{
// This is a degenerate case. The initializer is constant zero so the
// length of the string must be zero.
len = 0;
return true;
}
// Must be a Constant Array
ConstantArray* A = dyn_cast<ConstantArray>(INTLZR);
if (!A)
return false;
// Get the number of elements in the array
uint64_t max_elems = A->getType()->getNumElements();
// Traverse the constant array from start_idx (derived above) which is
// the place the GEP refers to in the array.
for ( len = start_idx; len < max_elems; len++)
{
if (ConstantInt* CI = dyn_cast<ConstantInt>(A->getOperand(len)))
{
// Check for the null terminator
if (CI->isNullValue())
break; // we found end of string
}
else
return false; // This array isn't suitable, non-int initializer
}
if (len >= max_elems)
return false; // This array isn't null terminated
// Subtract out the initial value from the length
len -= start_idx;
return true; // success!
}
// TODO: Additional cases that we need to add to this file:
// 1. memmove -> memcpy if src is a global constant array
}
Reference in New Issue View Git Blame Copy Permalink