avoid infinite looping when folding vector multiplies of constants (PR22698)
We were missing a check for the following fold in DAGCombiner:
// fold (fmul (fmul x, c1), c2) -> (fmul x, (fmul c1, c2))
If 'x' is also a constant, then we shouldn't do anything. Otherwise, we could end up swapping the operands back and forth forever.
This should fix:
http://llvm.org/bugs/show_bug.cgi?id=22698
Differential Revision: http://reviews.llvm.org/D7917
llvm-svn: 230884
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 8722c62..9e2b5af 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -7453,14 +7453,23 @@
// Fold scalars or any vector constants (not just splats).
// This fold is done in general by InstCombine, but extra fmul insts
// may have been generated during lowering.
+ SDValue N00 = N0.getOperand(0);
SDValue N01 = N0.getOperand(1);
auto *BV1 = dyn_cast<BuildVectorSDNode>(N1);
+ auto *BV00 = dyn_cast<BuildVectorSDNode>(N00);
auto *BV01 = dyn_cast<BuildVectorSDNode>(N01);
- if ((N1CFP && isConstOrConstSplatFP(N01)) ||
- (BV1 && BV01 && BV1->isConstant() && BV01->isConstant())) {
- SDLoc SL(N);
- SDValue MulConsts = DAG.getNode(ISD::FMUL, SL, VT, N01, N1);
- return DAG.getNode(ISD::FMUL, SL, VT, N0.getOperand(0), MulConsts);
+
+ // Check 1: Make sure that the first operand of the inner multiply is NOT
+ // a constant. Otherwise, we may induce infinite looping.
+ if (!(isConstOrConstSplatFP(N00) || (BV00 && BV00->isConstant()))) {
+ // Check 2: Make sure that the second operand of the inner multiply and
+ // the second operand of the outer multiply are constants.
+ if ((N1CFP && isConstOrConstSplatFP(N01)) ||
+ (BV1 && BV01 && BV1->isConstant() && BV01->isConstant())) {
+ SDLoc SL(N);
+ SDValue MulConsts = DAG.getNode(ISD::FMUL, SL, VT, N01, N1);
+ return DAG.getNode(ISD::FMUL, SL, VT, N00, MulConsts);
+ }
}
}