From 02c42856431562376ac8280b57ad744ba83f1e38 Mon Sep 17 00:00:00 2001 From: Evan Cheng Date: Wed, 16 Jan 2008 23:11:54 +0000 Subject: 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 --- lib/CodeGen/SelectionDAG/DAGCombiner.cpp | 50 ++++++++++++++++++++++++++++---- 1 file changed, 44 insertions(+), 6 deletions(-) (limited to 'lib/CodeGen') 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 @@ SDOperand DAGCombiner::visitLOAD(SDNode *N) { 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 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 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! } } } -- cgit v1.1