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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@78619 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 42d163f79b1136d405c10e8585a74e0c969d9621..d4d13884cb0c3c6da90e4172b5af151dd9326331 100644 (file)
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -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!

diff --git a/test/CodeGen/X86/extract-extract.ll b/test/CodeGen/X86/extract-extract.ll
new file mode 100644 (file)
index 0000000..1e0ce9a
--- /dev/null
+++ b/test/CodeGen/X86/extract-extract.ll
@@ -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
+}
+
+