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If a variable can only hold two values, and is not already a bool, shrink it

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down to actually BE a bool.  This allows simple value range propagation
stuff work harder, deleting comparisons in bzip2 in some hot loops.

This implements GlobalOpt/integer-bool.ll, which is the essence of the
loop condition distilled into a testcase.

llvm-svn: 18817
This commit is contained in:
Chris Lattner 2004-12-12 05:53:50 +00:00
parent ff477f8594
commit f125dc0e49
1 changed files with 78 additions and 22 deletions
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100
lib/Transforms/IPO/GlobalOpt.cpp
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@ -38,6 +38,8 @@ namespace {
Statistic<> NumDeleted ("globalopt", "Number of globals deleted");
Statistic<> NumFnDeleted("globalopt", "Number of functions deleted");
Statistic<> NumGlobUses ("globalopt", "Number of global uses devirtualized");
Statistic<> NumShrunkToBool("globalopt",
"Number of global vars shrunk to booleans");
struct GlobalOpt : public ModulePass {
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
@ -817,6 +819,50 @@ static bool OptimizeOnceStoredGlobal(GlobalVariable *GV, Value *StoredOnceVal,
return false;
}
/// ShrinkGlobalToBoolean - At this point, we have learned that the only two
/// values ever stored into GV are its initializer and OtherVal.
static void ShrinkGlobalToBoolean(GlobalVariable *GV, Constant *OtherVal) {
// Create the new global, initializing it to false.
GlobalVariable *NewGV = new GlobalVariable(Type::BoolTy, false,
GlobalValue::InternalLinkage, ConstantBool::False, GV->getName()+".b");
GV->getParent()->getGlobalList().insert(GV, NewGV);
Constant *InitVal = GV->getInitializer();
assert(InitVal->getType() != Type::BoolTy && "No reason to shrink to bool!");
// If initialized to zero and storing one into the global, we can use a cast
// instead of a select to synthesize the desired value.
bool IsOneZero = false;
if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal))
IsOneZero = InitVal->isNullValue() && CI->equalsInt(1);
while (!GV->use_empty()) {
Instruction *UI = cast<Instruction>(GV->use_back());
if (StoreInst *SI = dyn_cast<StoreInst>(UI)) {
// Change the store into a boolean store.
bool StoringOther = SI->getOperand(0) == OtherVal;
// Only do this if we weren't storing a loaded value.
if (StoringOther || SI->getOperand(0) == InitVal)
new StoreInst(ConstantBool::get(StoringOther), NewGV, SI);
} else {
// Change the load into a load of bool then a select.
LoadInst *LI = cast<LoadInst>(UI);
std::string Name = LI->getName(); LI->setName("");
LoadInst *NLI = new LoadInst(NewGV, Name+".b", LI);
Value *NSI;
if (IsOneZero)
NSI = new CastInst(NLI, LI->getType(), Name, LI);
else
NSI = new SelectInst(NLI, OtherVal, InitVal, Name, LI);
LI->replaceAllUsesWith(NSI);
}
UI->eraseFromParent();
}
GV->eraseFromParent();
}
/// ProcessInternalGlobal - Analyze the specified global variable and optimize
/// it if possible. If we make a change, return true.
bool GlobalOpt::ProcessInternalGlobal(GlobalVariable *GV,
@ -875,35 +921,45 @@ bool GlobalOpt::ProcessInternalGlobal(GlobalVariable *GV,
return true;
}
} else if (GS.StoredType == GlobalStatus::isStoredOnce) {
// If the initial value for the global was an undef value, and if only one
// other value was stored into it, we can just change the initializer to
// be an undef value, then delete all stores to the global. This allows
// us to mark it constant.
if (isa<UndefValue>(GV->getInitializer()) &&
isa<Constant>(GS.StoredOnceValue)) {
// Change the initial value here.
GV->setInitializer(cast<Constant>(GS.StoredOnceValue));
// Clean up any obviously simplifiable users now.
CleanupConstantGlobalUsers(GV, GV->getInitializer());
if (GV->use_empty()) {
DEBUG(std::cerr << " *** Substituting initializer allowed us to "
"simplify all users and delete global!\n");
GV->eraseFromParent();
++NumDeleted;
} else {
GVI = GV;
// If the initial value for the global was an undef value, and if only
// one other value was stored into it, we can just change the
// initializer to be an undef value, then delete all stores to the
// global. This allows us to mark it constant.
if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue))
if (isa<UndefValue>(GV->getInitializer())) {
// Change the initial value here.
GV->setInitializer(SOVConstant);
// Clean up any obviously simplifiable users now.
CleanupConstantGlobalUsers(GV, GV->getInitializer());
if (GV->use_empty()) {
DEBUG(std::cerr << " *** Substituting initializer allowed us to "
"simplify all users and delete global!\n");
GV->eraseFromParent();
++NumDeleted;
} else {
GVI = GV;
}
++NumSubstitute;
return true;
}
++NumSubstitute;
return true;
}
// Try to optimize globals based on the knowledge that only one value
// (besides its initializer) is ever stored to the global.
if (OptimizeOnceStoredGlobal(GV, GS.StoredOnceValue, GVI,
getAnalysis<TargetData>()))
return true;
// Otherwise, if the global was not a boolean, we can shrink it to be a
// boolean.
if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue))
if (GV->getType()->getElementType() != Type::BoolTy) {
DEBUG(std::cerr << " *** SHRINKING TO BOOL: " << *GV);
ShrinkGlobalToBoolean(GV, SOVConstant);
++NumShrunkToBool;
return true;
}
}
}
return false;