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https://github.com/c64scene-ar/llvm-6502.git
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Teach lint how to look through simple store+load pairs and other
effective no-op constructs, to make it more effective on unoptimized IR. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@104950 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman
parent
dd9344f3fa
commit
ff26d4e9ce
@ -35,7 +35,11 @@
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#include "llvm/Analysis/Passes.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/InstructionSimplify.h"
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#include "llvm/Analysis/ConstantFolding.h"
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#include "llvm/Analysis/Dominators.h"
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#include "llvm/Analysis/Lint.h"
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#include "llvm/Analysis/Loads.h"
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/Assembly/Writer.h"
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#include "llvm/Target/TargetData.h"
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@ -88,9 +92,12 @@ namespace {
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void visitInsertElementInst(InsertElementInst &I);
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void visitUnreachableInst(UnreachableInst &I);
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Value *findValue(Value *V, bool OffsetOk) const;
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public:
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Module *Mod;
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AliasAnalysis *AA;
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DominatorTree *DT;
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TargetData *TD;
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std::string Messages;
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@ -104,6 +111,7 @@ namespace {
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.setPreservesAll();
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AU.addRequired<AliasAnalysis>();
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AU.addRequired<DominatorTree>();
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}
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virtual void print(raw_ostream &O, const Module *M) const {}
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@ -176,6 +184,7 @@ X("lint", "Statically lint-checks LLVM IR", false, true);
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bool Lint::runOnFunction(Function &F) {
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Mod = F.getParent();
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AA = &getAnalysis<AliasAnalysis>();
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DT = &getAnalysis<DominatorTree>();
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TD = getAnalysisIfAvailable<TargetData>();
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visit(F);
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dbgs() << MessagesStr.str();
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@ -196,7 +205,7 @@ void Lint::visitCallSite(CallSite CS) {
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visitMemoryReference(I, Callee, 0, 0, MemRef::Callee);
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if (Function *F = dyn_cast<Function>(Callee->stripPointerCasts())) {
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if (Function *F = dyn_cast<Function>(findValue(Callee, /*OffsetOk=*/false))) {
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Assert1(CS.getCallingConv() == F->getCallingConv(),
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"Undefined behavior: Caller and callee calling convention differ",
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&I);
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@ -222,7 +231,7 @@ void Lint::visitCallSite(CallSite CS) {
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if (CS.isCall() && cast<CallInst>(CS.getInstruction())->isTailCall())
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for (CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
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AI != AE; ++AI) {
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Value *Obj = (*AI)->getUnderlyingObject();
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Value *Obj = findValue(*AI, /*OffsetOk=*/true);
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Assert1(!isa<AllocaInst>(Obj) && !isa<VAArgInst>(Obj),
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"Undefined behavior: Call with \"tail\" keyword references "
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"alloca or va_arg", &I);
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@ -247,7 +256,8 @@ void Lint::visitCallSite(CallSite CS) {
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// overlap is not distinguished from the case where nothing is known.
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unsigned Size = 0;
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if (const ConstantInt *Len =
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dyn_cast<ConstantInt>(MCI->getLength()->stripPointerCasts()))
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dyn_cast<ConstantInt>(findValue(MCI->getLength(),
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/*OffsetOk=*/false)))
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if (Len->getValue().isIntN(32))
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Size = Len->getValue().getZExtValue();
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Assert1(AA->alias(MCI->getSource(), Size, MCI->getDest(), Size) !=
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@ -312,7 +322,7 @@ void Lint::visitReturnInst(ReturnInst &I) {
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&I);
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if (Value *V = I.getReturnValue()) {
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Value *Obj = V->getUnderlyingObject();
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Value *Obj = findValue(V, /*OffsetOk=*/true);
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Assert1(!isa<AllocaInst>(Obj) && !isa<VAArgInst>(Obj),
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"Unusual: Returning alloca or va_arg value", &I);
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}
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@ -322,7 +332,7 @@ void Lint::visitReturnInst(ReturnInst &I) {
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void Lint::visitMemoryReference(Instruction &I,
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Value *Ptr, unsigned Align, const Type *Ty,
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unsigned Flags) {
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Value *UnderlyingObject = Ptr->getUnderlyingObject();
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Value *UnderlyingObject = findValue(Ptr, /*OffsetOk=*/true);
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Assert1(!isa<ConstantPointerNull>(UnderlyingObject),
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"Undefined behavior: Null pointer dereference", &I);
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Assert1(!isa<UndefValue>(UnderlyingObject),
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@ -390,21 +400,21 @@ void Lint::visitSub(BinaryOperator &I) {
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void Lint::visitLShr(BinaryOperator &I) {
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if (ConstantInt *CI =
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dyn_cast<ConstantInt>(I.getOperand(1)->stripPointerCasts()))
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dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
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Assert1(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
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"Undefined result: Shift count out of range", &I);
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}
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void Lint::visitAShr(BinaryOperator &I) {
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if (ConstantInt *CI =
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dyn_cast<ConstantInt>(I.getOperand(1)->stripPointerCasts()))
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dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
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Assert1(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
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"Undefined result: Shift count out of range", &I);
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}
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void Lint::visitShl(BinaryOperator &I) {
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if (ConstantInt *CI =
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dyn_cast<ConstantInt>(I.getOperand(1)->stripPointerCasts()))
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dyn_cast<ConstantInt>(findValue(I.getOperand(1), /*OffsetOk=*/false)))
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Assert1(CI->getValue().ult(cast<IntegerType>(I.getType())->getBitWidth()),
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"Undefined result: Shift count out of range", &I);
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}
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@ -458,14 +468,16 @@ void Lint::visitIndirectBrInst(IndirectBrInst &I) {
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void Lint::visitExtractElementInst(ExtractElementInst &I) {
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if (ConstantInt *CI =
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dyn_cast<ConstantInt>(I.getIndexOperand()->stripPointerCasts()))
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dyn_cast<ConstantInt>(findValue(I.getIndexOperand(),
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/*OffsetOk=*/false)))
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Assert1(CI->getValue().ult(I.getVectorOperandType()->getNumElements()),
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"Undefined result: extractelement index out of range", &I);
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}
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void Lint::visitInsertElementInst(InsertElementInst &I) {
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if (ConstantInt *CI =
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dyn_cast<ConstantInt>(I.getOperand(2)->stripPointerCasts()))
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dyn_cast<ConstantInt>(findValue(I.getOperand(2),
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/*OffsetOk=*/false)))
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Assert1(CI->getValue().ult(I.getType()->getNumElements()),
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"Undefined result: insertelement index out of range", &I);
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}
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@ -478,6 +490,59 @@ void Lint::visitUnreachableInst(UnreachableInst &I) {
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"side effects", &I);
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}
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/// findValue - Look through bitcasts and simple memory reference patterns
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/// to identify an equivalent, but more informative, value. If OffsetOk
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/// is true, look through getelementptrs with non-zero offsets too.
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///
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/// Most analysis passes don't require this logic, because instcombine
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/// will simplify most of these kinds of things away. But it's a goal of
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/// this Lint pass to be useful even on non-optimized IR.
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Value *Lint::findValue(Value *V, bool OffsetOk) const {
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// TODO: Look through sext or zext cast, when the result is known to
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// be interpreted as signed or unsigned, respectively.
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// TODO: Look through calls with unique return values.
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// TODO: Look through vector insert/extract/shuffle.
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V = OffsetOk ? V->getUnderlyingObject() : V->stripPointerCasts();
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if (LoadInst *L = dyn_cast<LoadInst>(V)) {
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BasicBlock::iterator BBI = L;
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BasicBlock *BB = L->getParent();
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for (;;) {
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if (Value *U = FindAvailableLoadedValue(L->getPointerOperand(),
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BB, BBI, 6, AA))
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return findValue(U, OffsetOk);
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BB = L->getParent()->getUniquePredecessor();
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if (!BB) break;
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BBI = BB->end();
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}
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} else if (CastInst *CI = dyn_cast<CastInst>(V)) {
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if (CI->isNoopCast(TD ? TD->getIntPtrType(V->getContext()) :
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Type::getInt64Ty(V->getContext())))
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return findValue(CI->getOperand(0), OffsetOk);
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} else if (PHINode *PN = dyn_cast<PHINode>(V)) {
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if (Value *W = PN->hasConstantValue(DT))
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return findValue(W, OffsetOk);
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} else if (ExtractValueInst *Ex = dyn_cast<ExtractValueInst>(V)) {
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if (Value *W = FindInsertedValue(Ex->getAggregateOperand(),
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Ex->idx_begin(),
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Ex->idx_end()))
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if (W != V)
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return findValue(W, OffsetOk);
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}
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// As a last resort, try SimplifyInstruction or constant folding.
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if (Instruction *Inst = dyn_cast<Instruction>(V)) {
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if (Value *W = SimplifyInstruction(Inst, TD))
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if (W != Inst)
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return findValue(W, OffsetOk);
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} else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
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if (Value *W = ConstantFoldConstantExpression(CE, TD))
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if (W != V)
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return findValue(W, OffsetOk);
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}
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return V;
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}
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//===----------------------------------------------------------------------===//
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// Implement the public interfaces to this file...
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//===----------------------------------------------------------------------===//
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@ -104,3 +104,24 @@ define i8* @return_local(i32 %n, i32 %m) {
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%s = getelementptr i8* %t, i32 %m
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ret i8* %s
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}
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; CHECK: Unusual: Returning alloca or va_arg value
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define i32* @return_obscured_local() {
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entry:
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%retval = alloca i32*
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%x = alloca i32
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store i32* %x, i32** %retval
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br label %next
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next:
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%t0 = load i32** %retval
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%t1 = insertvalue { i32, i32, i32* } zeroinitializer, i32* %t0, 2
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%t2 = extractvalue { i32, i32, i32* } %t1, 2
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br label %exit
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exit:
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%t3 = phi i32* [ %t2, %next ]
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%t4 = bitcast i32* %t3 to i32*
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%t5 = ptrtoint i32* %t4 to i64
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%t6 = add i64 %t5, 0
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%t7 = inttoptr i64 %t6 to i32*
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ret i32* %t7
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}
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