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refactor some code into a new TryToOptimizeStoreOfMallocToGlobal function.

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Use GetElementPtrInst::hasAllZeroIndices where possible.

llvm-svn: 61045
This commit is contained in:
Chris Lattner 2008-12-15 21:02:25 +00:00
parent dd4c8f09fa
commit 592852605f
1 changed files with 66 additions and 62 deletions
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128
lib/Transforms/IPO/GlobalOpt.cpp
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@ -1272,6 +1272,69 @@ static GlobalVariable *PerformHeapAllocSRoA(GlobalVariable *GV, MallocInst *MI){
return FieldGlobals[0];
}
/// TryToOptimizeStoreOfMallocToGlobal - This function is called when we see a
/// pointer global variable with a single value stored it that is a malloc or
/// cast of malloc.
static bool TryToOptimizeStoreOfMallocToGlobal(GlobalVariable *GV,
MallocInst *MI,
Module::global_iterator &GVI,
TargetData &TD) {
// If this is a malloc of an abstract type, don't touch it.
if (!MI->getAllocatedType()->isSized())
return false;
// We can't optimize this global unless all uses of it are *known* to be
// of the malloc value, not of the null initializer value (consider a use
// that compares the global's value against zero to see if the malloc has
// been reached). To do this, we check to see if all uses of the global
// would trap if the global were null: this proves that they must all
// happen after the malloc.
if (!AllUsesOfLoadedValueWillTrapIfNull(GV))
return false;
// We can't optimize this if the malloc itself is used in a complex way,
// for example, being stored into multiple globals. This allows the
// malloc to be stored into the specified global, loaded setcc'd, and
// GEP'd. These are all things we could transform to using the global
// for.
{
SmallPtrSet<PHINode*, 8> PHIs;
if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(MI, GV, PHIs))
return false;
}
// If we have a global that is only initialized with a fixed size malloc,
// transform the program to use global memory instead of malloc'd memory.
// This eliminates dynamic allocation, avoids an indirection accessing the
// data, and exposes the resultant global to further GlobalOpt.
if (ConstantInt *NElements = dyn_cast<ConstantInt>(MI->getArraySize())) {
// Restrict this transformation to only working on small allocations
// (2048 bytes currently), as we don't want to introduce a 16M global or
// something.
if (NElements->getZExtValue()*
TD.getABITypeSize(MI->getAllocatedType()) < 2048) {
GVI = OptimizeGlobalAddressOfMalloc(GV, MI);
return true;
}
}
// If the allocation is an array of structures, consider transforming this
// into multiple malloc'd arrays, one for each field. This is basically
// SRoA for malloc'd memory.
if (const StructType *AllocTy =
dyn_cast<StructType>(MI->getAllocatedType())) {
// This the structure has an unreasonable number of fields, leave it
// alone.
if (AllocTy->getNumElements() <= 16 && AllocTy->getNumElements() > 0 &&
GlobalLoadUsesSimpleEnoughForHeapSRA(GV, MI)) {
GVI = PerformHeapAllocSRoA(GV, MI);
return true;
}
}
return false;
}
// OptimizeOnceStoredGlobal - Try to optimize globals based on the knowledge
// that only one value (besides its initializer) is ever stored to the global.
@ -1282,15 +1345,7 @@ static bool OptimizeOnceStoredGlobal(GlobalVariable *GV, Value *StoredOnceVal,
StoredOnceVal = CI->getOperand(0);
else if (GetElementPtrInst *GEPI =dyn_cast<GetElementPtrInst>(StoredOnceVal)){
// "getelementptr Ptr, 0, 0, 0" is really just a cast.
bool IsJustACast = true;
for (User::op_iterator i = GEPI->op_begin() + 1, e = GEPI->op_end();
i != e; ++i)
if (!isa<Constant>(*i) ||
!cast<Constant>(*i)->isNullValue()) {
IsJustACast = false;
break;
}
if (IsJustACast)
if (GEPI->hasAllZeroIndices())
StoredOnceVal = GEPI->getOperand(0);
}
@ -1308,59 +1363,8 @@ static bool OptimizeOnceStoredGlobal(GlobalVariable *GV, Value *StoredOnceVal,
if (OptimizeAwayTrappingUsesOfLoads(GV, SOVC))
return true;
} else if (MallocInst *MI = dyn_cast<MallocInst>(StoredOnceVal)) {
// If this is a malloc of an abstract type, don't touch it.
if (!MI->getAllocatedType()->isSized())
return false;
// We can't optimize this global unless all uses of it are *known* to be
// of the malloc value, not of the null initializer value (consider a use
// that compares the global's value against zero to see if the malloc has
// been reached). To do this, we check to see if all uses of the global
// would trap if the global were null: this proves that they must all
// happen after the malloc.
if (!AllUsesOfLoadedValueWillTrapIfNull(GV))
return false;
// We can't optimize this if the malloc itself is used in a complex way,
// for example, being stored into multiple globals. This allows the
// malloc to be stored into the specified global, loaded setcc'd, and
// GEP'd. These are all things we could transform to using the global
// for.
{
SmallPtrSet<PHINode*, 8> PHIs;
if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(MI, GV, PHIs))
return false;
}
// If we have a global that is only initialized with a fixed size malloc,
// transform the program to use global memory instead of malloc'd memory.
// This eliminates dynamic allocation, avoids an indirection accessing the
// data, and exposes the resultant global to further GlobalOpt.
if (ConstantInt *NElements = dyn_cast<ConstantInt>(MI->getArraySize())) {
// Restrict this transformation to only working on small allocations
// (2048 bytes currently), as we don't want to introduce a 16M global or
// something.
if (NElements->getZExtValue()*
TD.getABITypeSize(MI->getAllocatedType()) < 2048) {
GVI = OptimizeGlobalAddressOfMalloc(GV, MI);
return true;
}
}
// If the allocation is an array of structures, consider transforming this
// into multiple malloc'd arrays, one for each field. This is basically
// SRoA for malloc'd memory.
if (const StructType *AllocTy =
dyn_cast<StructType>(MI->getAllocatedType())) {
// This the structure has an unreasonable number of fields, leave it
// alone.
if (AllocTy->getNumElements() <= 16 && AllocTy->getNumElements() > 0 &&
GlobalLoadUsesSimpleEnoughForHeapSRA(GV, MI)) {
GVI = PerformHeapAllocSRoA(GV, MI);
return true;
}
}
if (TryToOptimizeStoreOfMallocToGlobal(GV, MI, GVI, TD))
return true;
}
}