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Fix a bug in the DAGCombiner's handling of multiple linked 

MERGE_VALUES nodes. Replacing the result values with the
operands in one MERGE_VALUES node may cause another
MERGE_VALUES node be CSE'd with the first one, and bring
its uses along, so that the first one isn't dead, as this
code expects. Fix this by iterating until the node is
really dead. This fixes PR4699.

llvm-svn: 78619
This commit is contained in:
Dan Gohman 2009-08-10 23:43:19 +00:00
parent 733a64db57
commit 9d26c85bdc
2 changed files with 32 additions and 3 deletions
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11
llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
View File

@ -924,9 +924,14 @@ SDValue DAGCombiner::visitTokenFactor(SDNode *N) {
/// MERGE_VALUES can always be eliminated.
SDValue DAGCombiner::visitMERGE_VALUES(SDNode *N) {
WorkListRemover DeadNodes(*this);
for (unsigned i = 0, e = N->getNumOperands(); i != e; ++i)
DAG.ReplaceAllUsesOfValueWith(SDValue(N, i), N->getOperand(i),
&DeadNodes);
// Replacing results may cause a different MERGE_VALUES to suddenly
// be CSE'd with N, and carry its uses with it. Iterate until no
// uses remain, to ensure that the node can be safely deleted.
do {
for (unsigned i = 0, e = N->getNumOperands(); i != e; ++i)
DAG.ReplaceAllUsesOfValueWith(SDValue(N, i), N->getOperand(i),
&DeadNodes);
} while (!N->use_empty());
removeFromWorkList(N);
DAG.DeleteNode(N);
return SDValue(N, 0); // Return N so it doesn't get rechecked!

24
llvm/test/CodeGen/X86/extract-extract.ll Normal file
View File

@ -0,0 +1,24 @@
; RUN: llvm-as < %s | llc -march=x86 >/dev/null
; PR4699
; Handle this extractvalue-of-extractvalue case without getting in
; trouble with CSE in DAGCombine.
%cc = type { %crd }
%cr = type { i32 }
%crd = type { i64, %cr* }
%pp = type { %cc }
define fastcc void @foo(%pp* nocapture byval %p_arg) {
entry:
%tmp2 = getelementptr %pp* %p_arg, i64 0, i32 0 ; <%cc*> [#uses=
%tmp3 = load %cc* %tmp2 ; <%cc> [#uses=1]
%tmp34 = extractvalue %cc %tmp3, 0 ; <%crd> [#uses=1]
%tmp345 = extractvalue %crd %tmp34, 0 ; <i64> [#uses=1]
%.ptr.i = load %cr** undef ; <%cr*> [#uses=0]
%tmp15.i = shl i64 %tmp345, 3 ; <i64> [#uses=0]
store %cr* undef, %cr** undef
ret void
}