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Implement Transforms/SCCP/ipsccp-gvar.ll, by tracking values stored to

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non-address-taken global variables.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@18790 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2004-12-11 05:15:59 +00:00
parent 0982145d85
commit dd336d196e
1 changed files with 85 additions and 12 deletions
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97
lib/Transforms/Scalar/SCCP.cpp
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@ -25,11 +25,9 @@
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/IPO.h"
#include "llvm/Constants.h"
#include "llvm/Function.h"
#include "llvm/GlobalVariable.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Instructions.h"
#include "llvm/Pass.h"
#include "llvm/Type.h"
#include "llvm/Support/InstVisitor.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Support/CallSite.h"
@ -99,6 +97,12 @@ class SCCPSolver : public InstVisitor<SCCPSolver> {
std::set<BasicBlock*> BBExecutable;// The basic blocks that are executable
hash_map<Value*, LatticeVal> ValueState; // The state each value is in...
/// GlobalValue - If we are tracking any values for the contents of a global
/// variable, we keep a mapping from the constant accessor to the element of
/// the global, to the currently known value. If the value becomes
/// overdefined, it's entry is simply removed from this map.
hash_map<GlobalVariable*, LatticeVal> TrackedGlobals;
/// TrackedFunctionRetVals - If we are tracking arguments into and the return
/// value out of a function, it will have an entry in this map, indicating
/// what the known return value for the function is.
@ -134,11 +138,18 @@ public:
BBWorkList.push_back(BB); // Add the block to the work list!
}
/// TrackValueOfGlobalVariableIfPossible - Clients can use this method to
/// TrackValueOfGlobalVariable - Clients can use this method to
/// inform the SCCPSolver that it should track loads and stores to the
/// specified global variable if it can. This is only legal to call if
/// performing Interprocedural SCCP.
void TrackValueOfGlobalVariableIfPossible(GlobalVariable *GV);
void TrackValueOfGlobalVariable(GlobalVariable *GV) {
const Type *ElTy = GV->getType()->getElementType();
if (ElTy->isFirstClassType()) {
LatticeVal &IV = TrackedGlobals[GV];
if (!isa<UndefValue>(GV->getInitializer()))
IV.markConstant(GV->getInitializer());
}
}
/// AddTrackedFunction - If the SCCP solver is supposed to track calls into
/// and out of the specified function (which cannot have its address taken),
@ -178,6 +189,12 @@ public:
return TrackedFunctionRetVals;
}
/// getTrackedGlobals - Get and return the set of inferred initializers for
/// global variables.
const hash_map<GlobalVariable*, LatticeVal> &getTrackedGlobals() {
return TrackedGlobals;
}
private:
// markConstant - Make a value be marked as "constant". If the value
@ -303,7 +320,7 @@ private:
void visitShiftInst(ShiftInst &I) { visitBinaryOperator(I); }
// Instructions that cannot be folded away...
void visitStoreInst (Instruction &I) { /*returns void*/ }
void visitStoreInst (Instruction &I);
void visitLoadInst (LoadInst &I);
void visitGetElementPtrInst(GetElementPtrInst &I);
void visitCallInst (CallInst &I) { visitCallSite(CallSite::get(&I)); }
@ -724,6 +741,22 @@ static Constant *GetGEPGlobalInitializer(Constant *C, ConstantExpr *CE) {
return C;
}
void SCCPSolver::visitStoreInst(Instruction &SI) {
if (TrackedGlobals.empty() || !isa<GlobalVariable>(SI.getOperand(1)))
return;
GlobalVariable *GV = cast<GlobalVariable>(SI.getOperand(1));
hash_map<GlobalVariable*, LatticeVal>::iterator I = TrackedGlobals.find(GV);
if (I == TrackedGlobals.end() || I->second.isOverdefined()) return;
// Get the value we are storing into the global.
LatticeVal &PtrVal = getValueState(SI.getOperand(0));
mergeInValue(I->second, GV, PtrVal);
if (I->second.isOverdefined())
TrackedGlobals.erase(I); // No need to keep tracking this!
}
// Handle load instructions. If the operand is a constant pointer to a constant
// global, we can replace the load with the loaded constant value!
void SCCPSolver::visitLoadInst(LoadInst &I) {
@ -741,11 +774,22 @@ void SCCPSolver::visitLoadInst(LoadInst &I) {
}
// Transform load (constant global) into the value loaded.
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr))
if (GV->isConstant() && !GV->isExternal()) {
markConstant(IV, &I, GV->getInitializer());
return;
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
if (GV->isConstant()) {
if (!GV->isExternal()) {
markConstant(IV, &I, GV->getInitializer());
return;
}
} else if (!TrackedGlobals.empty()) {
// If we are tracking this global, merge in the known value for it.
hash_map<GlobalVariable*, LatticeVal>::iterator It =
TrackedGlobals.find(GV);
if (It != TrackedGlobals.end()) {
mergeInValue(IV, &I, It->second);
return;
}
}
}
// Transform load (constantexpr_GEP global, 0, ...) into the value loaded.
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
@ -1029,6 +1073,8 @@ namespace {
Statistic<> IPNumDeadBlocks ("ipsccp", "Number of basic blocks unreachable");
Statistic<> IPNumArgsElimed ("ipsccp",
"Number of arguments constant propagated");
Statistic<> IPNumGlobalConst("ipsccp",
"Number of globals found to be constant");
//===--------------------------------------------------------------------===//
//
@ -1053,7 +1099,8 @@ static bool AddressIsTaken(GlobalValue *GV) {
for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end();
UI != E; ++UI)
if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
if (SI->getOperand(0) == GV) return true; // Storing addr of GV.
if (SI->getOperand(0) == GV || SI->isVolatile())
return true; // Storing addr of GV.
} else if (isa<InvokeInst>(*UI) || isa<CallInst>(*UI)) {
// Make sure we are calling the function, not passing the address.
CallSite CS = CallSite::get(cast<Instruction>(*UI));
@ -1061,7 +1108,10 @@ static bool AddressIsTaken(GlobalValue *GV) {
E = CS.arg_end(); AI != E; ++AI)
if (*AI == GV)
return true;
} else if (!isa<LoadInst>(*UI)) {
} else if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
if (LI->isVolatile())
return true;
} else {
return true;
}
return false;
@ -1084,6 +1134,13 @@ bool IPSCCP::runOnModule(Module &M) {
Solver.AddTrackedFunction(F);
}
// Loop over global variables. We inform the solver about any internal global
// variables that do not have their 'addresses taken'. If they don't have
// their addresses taken, we can propagate constants through them.
for (Module::giterator G = M.gbegin(), E = M.gend(); G != E; ++G)
if (!G->isConstant() && G->hasInternalLinkage() && !AddressIsTaken(G))
Solver.TrackValueOfGlobalVariable(G);
// Solve for constants.
bool ResolvedBranches = true;
while (ResolvedBranches) {
@ -1208,6 +1265,22 @@ bool IPSCCP::runOnModule(Module &M) {
if (!isa<UndefValue>(RI->getOperand(0)))
RI->setOperand(0, UndefValue::get(F->getReturnType()));
}
// If we infered constant or undef values for globals variables, we can delete
// the global and any stores that remain to it.
const hash_map<GlobalVariable*, LatticeVal> &TG = Solver.getTrackedGlobals();
for (hash_map<GlobalVariable*, LatticeVal>::const_iterator I = TG.begin(),
E = TG.end(); I != E; ++I) {
GlobalVariable *GV = I->first;
assert(!I->second.isOverdefined() &&
"Overdefined values should have been taken out of the map!");
DEBUG(std::cerr << "Found that GV '" << GV->getName()<< "' is constant!\n");
while (!GV->use_empty()) {
StoreInst *SI = cast<StoreInst>(GV->use_back());
SI->eraseFromParent();
}
M.getGlobalList().erase(GV);
}
return MadeChanges;
}