Fixes a nasty dag combiner bug that causes a bunch of tests to fail at -O0.
It's not safe to use the two value CombineTo variant to combine away a dead load.
e.g.
v1, chain2 = load chain1, loc
v2, chain3 = load chain2, loc
v3 = add v2, c
Now we replace use of v1 with undef, use of chain2 with chain1.
ReplaceAllUsesWith() will iterate through uses of the first load and update operands:
v1, chain2 = load chain1, loc
v2, chain3 = load chain1, loc
v3 = add v2, c
Now the second load is the same as the first load, SelectionDAG cse will ensure
the use of second load is replaced with the first load.
v1, chain2 = load chain1, loc
v3 = add v1, c
Then v1 is replaced with undef and bad things happen.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@46099 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 09e0c3e..80ba27f 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -4055,16 +4055,54 @@
if (!LD->isVolatile()) {
if (N->getValueType(1) == MVT::Other) {
// Unindexed loads.
- if (N->hasNUsesOfValue(0, 0))
- return CombineTo(N, DAG.getNode(ISD::UNDEF, N->getValueType(0)), Chain);
+ if (N->hasNUsesOfValue(0, 0)) {
+ // It's not safe to use the two value CombineTo variant here. e.g.
+ // v1, chain2 = load chain1, loc
+ // v2, chain3 = load chain2, loc
+ // v3 = add v2, c
+ // Now we replace use of v1 with undef, use of chain2 with chain1.
+ // ReplaceAllUsesWith() will iterate through uses of the first load and
+ // update operands:
+ // v1, chain2 = load chain1, loc
+ // v2, chain3 = load chain1, loc
+ // v3 = add v2, c
+ // Now the second load is the same as the first load, SelectionDAG cse
+ // will ensure the use of second load is replaced with the first load.
+ // v1, chain2 = load chain1, loc
+ // v3 = add v1, c
+ // Then v1 is replaced with undef and bad things happen.
+ std::vector<SDNode*> NowDead;
+ SDOperand Undef = DAG.getNode(ISD::UNDEF, N->getValueType(0));
+ DOUT << "\nReplacing.6 "; DEBUG(N->dump(&DAG));
+ DOUT << "\nWith: "; DEBUG(Undef.Val->dump(&DAG));
+ DOUT << " and 1 other value\n";
+ DAG.ReplaceAllUsesOfValueWith(SDOperand(N, 0), Undef, &NowDead);
+ DAG.ReplaceAllUsesOfValueWith(SDOperand(N, 1), Chain, &NowDead);
+ removeFromWorkList(N);
+ for (unsigned i = 0, e = NowDead.size(); i != e; ++i)
+ removeFromWorkList(NowDead[i]);
+ DAG.DeleteNode(N);
+ return SDOperand(N, 0); // Return N so it doesn't get rechecked!
+ }
} else {
// Indexed loads.
assert(N->getValueType(2) == MVT::Other && "Malformed indexed loads?");
if (N->hasNUsesOfValue(0, 0) && N->hasNUsesOfValue(0, 1)) {
- SDOperand Undef0 = DAG.getNode(ISD::UNDEF, N->getValueType(0));
- SDOperand Undef1 = DAG.getNode(ISD::UNDEF, N->getValueType(1));
- SDOperand To[] = { Undef0, Undef1, Chain };
- return CombineTo(N, To, 3);
+ std::vector<SDNode*> NowDead;
+ SDOperand Undef = DAG.getNode(ISD::UNDEF, N->getValueType(0));
+ DOUT << "\nReplacing.6 "; DEBUG(N->dump(&DAG));
+ DOUT << "\nWith: "; DEBUG(Undef.Val->dump(&DAG));
+ DOUT << " and 2 other values\n";
+ DAG.ReplaceAllUsesOfValueWith(SDOperand(N, 0), Undef, &NowDead);
+ DAG.ReplaceAllUsesOfValueWith(SDOperand(N, 1),
+ DAG.getNode(ISD::UNDEF, N->getValueType(1)),
+ &NowDead);
+ DAG.ReplaceAllUsesOfValueWith(SDOperand(N, 2), Chain, &NowDead);
+ removeFromWorkList(N);
+ for (unsigned i = 0, e = NowDead.size(); i != e; ++i)
+ removeFromWorkList(NowDead[i]);
+ DAG.DeleteNode(N);
+ return SDOperand(N, 0); // Return N so it doesn't get rechecked!
}
}
}