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Fix PR14060, an infinite loop in reassociate. The problem was that one of the

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operands of the expression being written was wrongly thought to be reusable as
an inner node of the expression resulting in it turning up as both an inner node
*and* a leaf, creating a cycle in the def-use graph.  This would have caused the
verifier to blow up if things had gotten that far, however it managed to provoke
an infinite loop first.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@168291 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan Sands 2012-11-18 19:27:01 +00:00
parent 085f6a4ac2
commit b8e1111fbf
2 changed files with 43 additions and 6 deletions
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30
lib/Transforms/Scalar/Reassociate.cpp
View File

@ -606,8 +606,8 @@ void Reassociate::RewriteExprTree(BinaryOperator *I,
SmallVectorImpl<ValueEntry> &Ops) {
assert(Ops.size() > 1 && "Single values should be used directly!");
// Since our optimizations never increase the number of operations, the new
// expression can always be written by reusing the existing binary operators
// Since our optimizations should never increase the number of operations, the
// new expression can usually be written reusing the existing binary operators
// from the original expression tree, without creating any new instructions,
// though the rewritten expression may have a completely different topology.
// We take care to not change anything if the new expression will be the same
@ -621,6 +621,20 @@ void Reassociate::RewriteExprTree(BinaryOperator *I,
unsigned Opcode = I->getOpcode();
BinaryOperator *Op = I;
/// NotRewritable - The operands being written will be the leaves of the new
/// expression and must not be used as inner nodes (via NodesToRewrite) by
/// mistake. Inner nodes are always reassociable, and usually leaves are not
/// (if they were they would have been incorporated into the expression and so
/// would not be leaves), so most of the time there is no danger of this. But
/// in rare cases a leaf may become reassociable if an optimization kills uses
/// of it, or it may momentarily become reassociable during rewriting (below)
/// due it being removed as an operand of one of its uses. Ensure that misuse
/// of leaf nodes as inner nodes cannot occur by remembering all of the future
/// leaves and refusing to reuse any of them as inner nodes.
SmallPtrSet<Value*, 8> NotRewritable;
for (unsigned i = 0, e = Ops.size(); i != e; ++i)
NotRewritable.insert(Ops[i].Op);
// ExpressionChanged - Non-null if the rewritten expression differs from the
// original in some non-trivial way, requiring the clearing of optional flags.
// Flags are cleared from the operator in ExpressionChanged up to I inclusive.
@ -653,12 +667,14 @@ void Reassociate::RewriteExprTree(BinaryOperator *I,
// the old operands with the new ones.
DEBUG(dbgs() << "RA: " << *Op << '\n');
if (NewLHS != OldLHS) {
if (BinaryOperator *BO = isReassociableOp(OldLHS, Opcode))
BinaryOperator *BO = isReassociableOp(OldLHS, Opcode);
if (BO && !NotRewritable.count(BO))
NodesToRewrite.push_back(BO);
Op->setOperand(0, NewLHS);
}
if (NewRHS != OldRHS) {
if (BinaryOperator *BO = isReassociableOp(OldRHS, Opcode))
BinaryOperator *BO = isReassociableOp(OldRHS, Opcode);
if (BO && !NotRewritable.count(BO))
NodesToRewrite.push_back(BO);
Op->setOperand(1, NewRHS);
}
@ -682,7 +698,8 @@ void Reassociate::RewriteExprTree(BinaryOperator *I,
Op->swapOperands();
} else {
// Overwrite with the new right-hand side.
if (BinaryOperator *BO = isReassociableOp(Op->getOperand(1), Opcode))
BinaryOperator *BO = isReassociableOp(Op->getOperand(1), Opcode);
if (BO && !NotRewritable.count(BO))
NodesToRewrite.push_back(BO);
Op->setOperand(1, NewRHS);
ExpressionChanged = Op;
@ -695,7 +712,8 @@ void Reassociate::RewriteExprTree(BinaryOperator *I,
// Now deal with the left-hand side. If this is already an operation node
// from the original expression then just rewrite the rest of the expression
// into it.
if (BinaryOperator *BO = isReassociableOp(Op->getOperand(0), Opcode)) {
BinaryOperator *BO = isReassociableOp(Op->getOperand(0), Opcode);
if (BO && !NotRewritable.count(BO)) {
Op = BO;
continue;
}

19
test/Transforms/Reassociate/crash.ll
View File

@ -153,3 +153,22 @@ define i32 @bar(i32 %arg, i32 %arg1, i32 %arg2) {
%ret = add i32 %tmp2, %tmp3
ret i32 %ret
}
; PR14060
define i8 @hang(i8 %p, i8 %p0, i8 %p1, i8 %p2, i8 %p3, i8 %p4, i8 %p5, i8 %p6, i8 %p7, i8 %p8, i8 %p9) {
%tmp = zext i1 false to i8
%tmp16 = or i8 %tmp, 1
%tmp22 = or i8 %p7, %p0
%tmp23 = or i8 %tmp16, %tmp22
%tmp28 = or i8 %p9, %p1
%tmp31 = or i8 %tmp23, %p2
%tmp32 = or i8 %tmp31, %tmp28
%tmp38 = or i8 %p8, %p3
%tmp39 = or i8 %tmp16, %tmp38
%tmp43 = or i8 %tmp39, %p4
%tmp44 = or i8 %tmp43, 1
%tmp47 = or i8 %tmp32, %p5
%tmp50 = or i8 %tmp47, %p6
%tmp51 = or i8 %tmp44, %tmp50
ret i8 %tmp51
}