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Fixes a nasty dag combiner bug that causes a bunch of tests to fail at -O0.

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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
This commit is contained in:
Evan Cheng 2008-01-16 23:11:54 +00:00
parent 339e14fbdc
commit 02c4285643
2 changed files with 74 additions and 6 deletions
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50
lib/CodeGen/SelectionDAG/DAGCombiner.cpp
View File

@ -4055,16 +4055,54 @@ SDOperand DAGCombiner::visitLOAD(SDNode *N) {
if (!LD->isVolatile()) { if (!LD->isVolatile()) {
if (N->getValueType(1) == MVT::Other) { if (N->getValueType(1) == MVT::Other) {
// Unindexed loads. // Unindexed loads.
if (N->hasNUsesOfValue(0, 0)) if (N->hasNUsesOfValue(0, 0)) {
return CombineTo(N, DAG.getNode(ISD::UNDEF, N->getValueType(0)), Chain); // 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 { } else {
// Indexed loads. // Indexed loads.
assert(N->getValueType(2) == MVT::Other && "Malformed indexed loads?"); assert(N->getValueType(2) == MVT::Other && "Malformed indexed loads?");
if (N->hasNUsesOfValue(0, 0) && N->hasNUsesOfValue(0, 1)) { if (N->hasNUsesOfValue(0, 0) && N->hasNUsesOfValue(0, 1)) {
SDOperand Undef0 = DAG.getNode(ISD::UNDEF, N->getValueType(0)); std::vector<SDNode*> NowDead;
SDOperand Undef1 = DAG.getNode(ISD::UNDEF, N->getValueType(1)); SDOperand Undef = DAG.getNode(ISD::UNDEF, N->getValueType(0));
SDOperand To[] = { Undef0, Undef1, Chain }; DOUT << "\nReplacing.6 "; DEBUG(N->dump(&DAG));
return CombineTo(N, To, 3); 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!
} }
} }
} }

30
test/CodeGen/X86/2008-01-16-InvalidDAGCombineXform.ll Normal file
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@ -0,0 +1,30 @@
; RUN: llvm-as < %s | llc -march=x86 | not grep IMPLICIT_DEF
%struct.node_t = type { double*, %struct.node_t*, %struct.node_t**, double**, double*, i32, i32 }
define void @localize_local_bb19_bb(%struct.node_t** %cur_node) {
newFuncRoot:
%tmp1 = load %struct.node_t** %cur_node, align 4 ; <%struct.node_t*> [#uses=1]
%tmp2 = getelementptr %struct.node_t* %tmp1, i32 0, i32 4 ; <double**> [#uses=1]
%tmp3 = load double** %tmp2, align 4 ; <double*> [#uses=1]
%tmp4 = load %struct.node_t** %cur_node, align 4 ; <%struct.node_t*> [#uses=1]
%tmp5 = getelementptr %struct.node_t* %tmp4, i32 0, i32 4 ; <double**> [#uses=1]
store double* %tmp3, double** %tmp5, align 4
%tmp6 = load %struct.node_t** %cur_node, align 4 ; <%struct.node_t*> [#uses=1]
%tmp7 = getelementptr %struct.node_t* %tmp6, i32 0, i32 3 ; <double***> [#uses=1]
%tmp8 = load double*** %tmp7, align 4 ; <double**> [#uses=1]
%tmp9 = load %struct.node_t** %cur_node, align 4 ; <%struct.node_t*> [#uses=1]
%tmp10 = getelementptr %struct.node_t* %tmp9, i32 0, i32 3 ; <double***> [#uses=1]
store double** %tmp8, double*** %tmp10, align 4
%tmp11 = load %struct.node_t** %cur_node, align 4 ; <%struct.node_t*> [#uses=1]
%tmp12 = getelementptr %struct.node_t* %tmp11, i32 0, i32 0 ; <double**> [#uses=1]
%tmp13 = load double** %tmp12, align 4 ; <double*> [#uses=1]
%tmp14 = load %struct.node_t** %cur_node, align 4 ; <%struct.node_t*> [#uses=1]
%tmp15 = getelementptr %struct.node_t* %tmp14, i32 0, i32 0 ; <double**> [#uses=1]
store double* %tmp13, double** %tmp15, align 4
%tmp16 = load %struct.node_t** %cur_node, align 4 ; <%struct.node_t*> [#uses=1]
%tmp17 = getelementptr %struct.node_t* %tmp16, i32 0, i32 1 ; <%struct.node_t**> [#uses=1]
%tmp18 = load %struct.node_t** %tmp17, align 4 ; <%struct.node_t*> [#uses=1]
store %struct.node_t* %tmp18, %struct.node_t** %cur_node, align 4
ret void
}