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llvm-svn: 21602
This commit is contained in:
Reid Spencer 2005-04-27 21:29:20 +00:00
parent 96704dee49
commit 49cfe25457
1 changed files with 71 additions and 54 deletions
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125
lib/Transforms/IPO/SimplifyLibCalls.cpp
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@ -37,23 +37,33 @@ namespace {
Statistic<> SimplifiedLibCalls("simplify-libcalls",
"Number of well-known library calls simplified");
/// @brief The list of optimizations deriving from LibCallOptimization
// 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 SimplifyLibCall pass will call the
/// 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. It will also call the
/// OptimizeCall method to perform, or attempt to perform, the optimization(s)
/// for the library call. Subclasses of this class are located toward the
/// end of this file.
/// 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
{
/// @brief Constructor that registers the optimization. The \p fname argument
/// must be the name of the library function being optimized by the subclass.
/// 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
@ -61,22 +71,23 @@ struct LibCallOptimization
, occurrences(stat_name.c_str(),"Number of calls simplified")
#endif
{
// Register this call optimizer
// Register this call optimizer in the optlist (a hash_map)
optlist[func_name] = this;
}
/// @brief Destructor
virtual ~LibCallOptimization() {}
/// @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
/// 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;
/// 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
@ -88,8 +99,6 @@ struct LibCallOptimization
/// 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.
/// @param ci the call instruction under consideration
/// @param f the function that ci calls.
/// @brief Optimize a call, if possible.
virtual bool OptimizeCall(
CallInst* ci, ///< The call instruction that should be optimized.
@ -100,7 +109,8 @@ struct LibCallOptimization
const char * getFunctionName() const { return func_name; }
#ifndef NDEBUG
void occurred() { ++occurrences; }
/// @brief Called by SimplifyLibCalls to update the occurrences statistic.
void succeeded() { ++occurrences; }
#endif
private:
@ -111,23 +121,19 @@ private:
#endif
};
/// This class is the base class for a set of small but important
/// optimizations of calls to well-known functions, such as those in the c
/// library.
/// 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 subclasses to
/// validate the call by calling ValidateLibraryCall. If it is validated, then
/// the OptimizeCall method is called.
/// 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
@ -137,6 +143,7 @@ struct SimplifyLibCalls : public ModulePass
/// 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);
@ -183,7 +190,7 @@ struct SimplifyLibCalls : public ModulePass
++SimplifiedLibCalls;
found_optimization = result = true;
#ifndef NDEBUG
CO->occurred();
CO->succeeded();
#endif
}
}
@ -230,10 +237,8 @@ struct SimplifyLibCalls : public ModulePass
return memcpy_func;
}
/// @brief Compute length of constant string
bool getConstantStringLength(Value* V, uint64_t& len );
private:
/// @brief Reset our cached data for a new Module
void reset(Module& mod)
{
M = &mod;
@ -243,10 +248,10 @@ private:
}
private:
Function* memcpy_func;
Function* strlen_func;
Module* M;
TargetData* TD;
Function* memcpy_func; ///< Cached llvm.memcpy function
Function* strlen_func; ///< Cached strlen function
Module* M; ///< Cached Module
TargetData* TD; ///< Cached TargetData
};
// Register the pass
@ -272,9 +277,8 @@ 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 as passed to the exit function. It assumes that the
/// instructions after the call to exit(3) can be deleted since they are
/// unreachable anyway.
/// 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
{
@ -335,16 +339,18 @@ struct ExitInMainOptimization : public LibCallOptimization
/// 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 array. In this case, if the array is small, we can generate a
/// series of inline store instructions to effect the concatenation without
/// calling strcat.
/// 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
@ -425,8 +431,8 @@ public:
}
} StrCatOptimizer;
/// This LibCallOptimization will simplify a call to the strcpy library function.
/// Several optimizations are possible:
/// 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.
@ -514,9 +520,9 @@ public:
}
} 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.
/// 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
{
@ -549,16 +555,20 @@ struct StrLenOptimization : public LibCallOptimization
}
} 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.
/// 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
@ -620,19 +630,27 @@ public:
}
} MemCpyOptimizer;
/// This LibCallOptimization will simplify a call to the memmove library function. /// It is identical to MemCopyOptimization except for the name of the intrinsic.
/// 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 string 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
/// 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");
@ -723,7 +741,6 @@ bool getConstantStringLength(Value* V, uint64_t& len )
return true; // success!
}
// TODO: Additional cases that we need to add to this file:
// 1. memmove -> memcpy if src is a global constant array
}