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Detect self-referential values.

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llvm-svn: 104957
This commit is contained in:
Dan Gohman 2010-05-28 16:45:33 +00:00
parent 0108e13d6c
commit 9a50a9215c
2 changed files with 30 additions and 6 deletions
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25
lib/Analysis/Lint.cpp
View File

@ -93,6 +93,8 @@ namespace {
void visitUnreachableInst(UnreachableInst &I);
Value *findValue(Value *V, bool OffsetOk) const;
Value *findValueImpl(Value *V, bool OffsetOk,
SmallPtrSet<Value *, 4> &Visited) const;
public:
Module *Mod;
@ -498,6 +500,17 @@ void Lint::visitUnreachableInst(UnreachableInst &I) {
/// will simplify most of these kinds of things away. But it's a goal of
/// this Lint pass to be useful even on non-optimized IR.
Value *Lint::findValue(Value *V, bool OffsetOk) const {
SmallPtrSet<Value *, 4> Visited;
return findValueImpl(V, OffsetOk, Visited);
}
/// findValueImpl - Implementation helper for findValue.
Value *Lint::findValueImpl(Value *V, bool OffsetOk,
SmallPtrSet<Value *, 4> &Visited) const {
// Detect self-referential values.
if (!Visited.insert(V))
return UndefValue::get(V->getType());
// TODO: Look through sext or zext cast, when the result is known to
// be interpreted as signed or unsigned, respectively.
// TODO: Look through calls with unique return values.
@ -509,7 +522,7 @@ Value *Lint::findValue(Value *V, bool OffsetOk) const {
for (;;) {
if (Value *U = FindAvailableLoadedValue(L->getPointerOperand(),
BB, BBI, 6, AA))
return findValue(U, OffsetOk);
return findValueImpl(U, OffsetOk, Visited);
BB = L->getParent()->getUniquePredecessor();
if (!BB) break;
BBI = BB->end();
@ -517,27 +530,27 @@ Value *Lint::findValue(Value *V, bool OffsetOk) const {
} else if (CastInst *CI = dyn_cast<CastInst>(V)) {
if (CI->isNoopCast(TD ? TD->getIntPtrType(V->getContext()) :
Type::getInt64Ty(V->getContext())))
return findValue(CI->getOperand(0), OffsetOk);
return findValueImpl(CI->getOperand(0), OffsetOk, Visited);
} else if (PHINode *PN = dyn_cast<PHINode>(V)) {
if (Value *W = PN->hasConstantValue(DT))
return findValue(W, OffsetOk);
return findValueImpl(W, OffsetOk, Visited);
} else if (ExtractValueInst *Ex = dyn_cast<ExtractValueInst>(V)) {
if (Value *W = FindInsertedValue(Ex->getAggregateOperand(),
Ex->idx_begin(),
Ex->idx_end()))
if (W != V)
return findValue(W, OffsetOk);
return findValueImpl(W, OffsetOk, Visited);
}
// As a last resort, try SimplifyInstruction or constant folding.
if (Instruction *Inst = dyn_cast<Instruction>(V)) {
if (Value *W = SimplifyInstruction(Inst, TD))
if (W != Inst)
return findValue(W, OffsetOk);
return findValueImpl(W, OffsetOk, Visited);
} else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
if (Value *W = ConstantFoldConstantExpression(CE, TD))
if (W != V)
return findValue(W, OffsetOk);
return findValueImpl(W, OffsetOk, Visited);
}
return V;

11
test/Other/lint.ll
View File

@ -122,3 +122,14 @@ exit:
%t7 = inttoptr i64 %t6 to i32*
ret i32* %t7
}
; CHECK: Undefined behavior: Undef pointer dereference
define i32* @self_reference() {
entry:
unreachable
exit:
%t3 = phi i32* [ %t4, %exit ]
%t4 = bitcast i32* %t3 to i32*
%x = volatile load i32* %t3
br label %exit
}