[llvm-commits] [llvm] r78619 - in /llvm/trunk: lib/CodeGen/SelectionDAG/DAGCombiner.cpp test/CodeGen/X86/extract-extract.ll

[Dan Gohman]

Author: djg
Date: Mon Aug 10 18:43:19 2009
New Revision: 78619

URL: http://llvm.org/viewvc/llvm-project?rev=78619&view=rev
Log:
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.

Added:
    llvm/trunk/test/CodeGen/X86/extract-extract.ll
Modified:
    llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp?rev=78619&r1=78618&r2=78619&view=diff

==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp Mon Aug 10 18:43:19 2009
@@ -924,9 +924,14 @@
 /// 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!

Added: llvm/trunk/test/CodeGen/X86/extract-extract.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/extract-extract.ll?rev=78619&view=auto

==============================================================================
--- llvm/trunk/test/CodeGen/X86/extract-extract.ll (added)
+++ llvm/trunk/test/CodeGen/X86/extract-extract.ll Mon Aug 10 18:43:19 2009
@@ -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
+}
+
+