Fix for PR#30562: Selection DAG error: Detected cycle in SelectionDAG.

avt77 · avt77 · commit 4e7bcd5216af · 2017-04-14T09:17:09.000Z
Patch by Dinar Temirbulatov

llvm-svn: 300314
diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
@@ -1192,8 +1192,11 @@ SDValue SelectionDAGLegalize::ExpandExtractFromVectorThroughStack(SDValue Op) {
 
       // If the index is dependent on the store we will introduce a cycle when
       // creating the load (the load uses the index, and by replacing the chain
-      // we will make the index dependent on the load).
-      if (SDNode::hasPredecessorHelper(ST, Visited, Worklist))
+      // we will make the index dependent on the load). Also, the store might be
+      // dependent on the extractelement and introduce a cycle when creating 
+      // the load.
+      if (SDNode::hasPredecessorHelper(ST, Visited, Worklist) ||
+          ST->hasPredecessor(Op.getNode()))
         continue;
 
       StackPtr = ST->getBasePtr();
diff --git a/llvm/test/CodeGen/X86/pr30562.ll b/llvm/test/CodeGen/X86/pr30562.ll
@@ -0,0 +1,22 @@
+; RUN: llc < %s -mtriple=x86_64-unknown-unknown | FileCheck %s
+
+define i32 @foo(i64* nocapture %perm, i32 %n) {
+entry:
+  br label %body
+
+body:
+; CHECK-LABEL: foo:
+; CHECK: pslldq  $8, %xmm0
+  %vec.ind = phi <2 x i64> [ <i64 0, i64 1>, %entry ], [ <i64 2, i64 3>, %body ]
+  %l13 = extractelement <2 x i64> %vec.ind, i32 %n
+  %l14 = getelementptr inbounds i64, i64* %perm, i64 %l13
+  %l15 = bitcast i64* %l14 to <2 x i64>*
+  store <2 x i64> %vec.ind, <2 x i64>* %l15, align 8
+  %niter.ncmp.3 = icmp eq i64 %l13, 0
+  br i1 %niter.ncmp.3, label %exit, label %body
+
+exit:
+  ret i32 %n
+
+}
+
