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[DAG] visitFREEZE - remove isGuaranteedNotToBeUndefOrPoison assertion (#146490)

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Although nice to have to prove the freeze can be moved, this can fail
immediately after freeze(op(...)) -> op(freeze(),freeze(),...) creation
if any of the new freeze nodes now prevents value tracking from seeing
through to the source values (e.g. shift amounts/element indices are in
bounds etc.).

This will allow us to remove the isGuaranteedNotToBeUndefOrPoison checks
inside canCreateUndefOrPoison that were discussed on #146361
This commit is contained in:
Simon Pilgrim
2025-07-01 11:17:41 +01:00
committed by GitHub
parent 2ee884a9db
commit 4e30f8101e
1 changed files with 19 additions and 22 deletions
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41
llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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@@ -16714,28 +16714,25 @@ SDValue DAGCombiner::visitFREEZE(SDNode *N) {
Op = DAG.getFreeze(Op);
}
SDValue R;
if (auto *SVN = dyn_cast<ShuffleVectorSDNode>(N0)) {
// Special case handling for ShuffleVectorSDNode nodes.
R = DAG.getVectorShuffle(N0.getValueType(), SDLoc(N0), Ops[0], Ops[1],
SVN->getMask());
} else {
// NOTE: this strips poison generating flags.
// Folding freeze(op(x, ...)) -> op(freeze(x), ...) does not require nnan,
// ninf, nsz, or fast.
// However, contract, reassoc, afn, and arcp should be preserved,
// as these fast-math flags do not introduce poison values.
SDNodeFlags SrcFlags = N0->getFlags();
SDNodeFlags SafeFlags;
SafeFlags.setAllowContract(SrcFlags.hasAllowContract());
SafeFlags.setAllowReassociation(SrcFlags.hasAllowReassociation());
SafeFlags.setApproximateFuncs(SrcFlags.hasApproximateFuncs());
SafeFlags.setAllowReciprocal(SrcFlags.hasAllowReciprocal());
R = DAG.getNode(N0.getOpcode(), SDLoc(N0), N0->getVTList(), Ops, SafeFlags);
}
assert(DAG.isGuaranteedNotToBeUndefOrPoison(R, /*PoisonOnly*/ false) &&
"Can't create node that may be undef/poison!");
return R;
SDLoc DL(N0);
// Special case handling for ShuffleVectorSDNode nodes.
if (auto *SVN = dyn_cast<ShuffleVectorSDNode>(N0))
return DAG.getVectorShuffle(N0.getValueType(), DL, Ops[0], Ops[1],
SVN->getMask());
// NOTE: this strips poison generating flags.
// Folding freeze(op(x, ...)) -> op(freeze(x), ...) does not require nnan,
// ninf, nsz, or fast.
// However, contract, reassoc, afn, and arcp should be preserved,
// as these fast-math flags do not introduce poison values.
SDNodeFlags SrcFlags = N0->getFlags();
SDNodeFlags SafeFlags;
SafeFlags.setAllowContract(SrcFlags.hasAllowContract());
SafeFlags.setAllowReassociation(SrcFlags.hasAllowReassociation());
SafeFlags.setApproximateFuncs(SrcFlags.hasApproximateFuncs());
SafeFlags.setAllowReciprocal(SrcFlags.hasAllowReciprocal());
return DAG.getNode(N0.getOpcode(), DL, N0->getVTList(), Ops, SafeFlags);
}
/// We know that BV is a build_vector node with Constant, ConstantFP or Undef