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Limit the recursion depth of SelectionDAG::isSplatValue()

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This method previously always recursively checked both the left-hand
side and right-hand side of binary operations for splatted (broadcast)
vector values to determine if the parent DAG node is a splat.

Like several other SelectionDAG methods, limit the recursion depth to
MaxRecursionDepth (6). This prevents stack overflow.
See also https://issuetracker.google.com/173785481

Patch by Nicolas Capens. Thanks!

Differential Revision: https://reviews.llvm.org/D92421
This commit is contained in:
Justin Bogner
2020-12-09 10:33:59 -08:00
parent be9b4bbdfc
commit e6a1187dd8
2 changed files with 10 additions and 6 deletions
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3
llvm/include/llvm/CodeGen/SelectionDAG.h
View File

@@ -1829,7 +1829,8 @@ public:
/// for \p DemandedElts.
///
/// NOTE: The function will return true for a demanded splat of UNDEF values.
bool isSplatValue(SDValue V, const APInt &DemandedElts, APInt &UndefElts);
bool isSplatValue(SDValue V, const APInt &DemandedElts, APInt &UndefElts,
unsigned Depth = 0);
/// Test whether \p V has a splatted value.
bool isSplatValue(SDValue V, bool AllowUndefs = false);

13
llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
View File

@@ -2355,13 +2355,16 @@ bool SelectionDAG::MaskedValueIsAllOnes(SDValue V, const APInt &Mask,
/// sense to specify which elements are demanded or undefined, therefore
/// they are simply ignored.
bool SelectionDAG::isSplatValue(SDValue V, const APInt &DemandedElts,
APInt &UndefElts) {
APInt &UndefElts, unsigned Depth) {
EVT VT = V.getValueType();
assert(VT.isVector() && "Vector type expected");
if (!VT.isScalableVector() && !DemandedElts)
return false; // No demanded elts, better to assume we don't know anything.
if (Depth >= MaxRecursionDepth)
return false; // Limit search depth.
// Deal with some common cases here that work for both fixed and scalable
// vector types.
switch (V.getOpcode()) {
@@ -2376,8 +2379,8 @@ bool SelectionDAG::isSplatValue(SDValue V, const APInt &DemandedElts,
APInt UndefLHS, UndefRHS;
SDValue LHS = V.getOperand(0);
SDValue RHS = V.getOperand(1);
if (isSplatValue(LHS, DemandedElts, UndefLHS) &&
isSplatValue(RHS, DemandedElts, UndefRHS)) {
if (isSplatValue(LHS, DemandedElts, UndefLHS, Depth + 1) &&
isSplatValue(RHS, DemandedElts, UndefRHS, Depth + 1)) {
UndefElts = UndefLHS | UndefRHS;
return true;
}
@@ -2386,7 +2389,7 @@ bool SelectionDAG::isSplatValue(SDValue V, const APInt &DemandedElts,
case ISD::TRUNCATE:
case ISD::SIGN_EXTEND:
case ISD::ZERO_EXTEND:
return isSplatValue(V.getOperand(0), DemandedElts, UndefElts);
return isSplatValue(V.getOperand(0), DemandedElts, UndefElts, Depth + 1);
}
// We don't support other cases than those above for scalable vectors at
@@ -2441,7 +2444,7 @@ bool SelectionDAG::isSplatValue(SDValue V, const APInt &DemandedElts,
unsigned NumSrcElts = Src.getValueType().getVectorNumElements();
APInt UndefSrcElts;
APInt DemandedSrcElts = DemandedElts.zextOrSelf(NumSrcElts).shl(Idx);
if (isSplatValue(Src, DemandedSrcElts, UndefSrcElts)) {
if (isSplatValue(Src, DemandedSrcElts, UndefSrcElts, Depth + 1)) {
UndefElts = UndefSrcElts.extractBits(NumElts, Idx);
return true;
}