[PATCH] D57921: [DAG] Cleanup unused node in SimplifySelectCC.

[Nirav Dave via Phabricator via llvm-commits]

niravd created this revision.
niravd added reviewers: spatel, RKSimon, craig.topper.
Herald added a subscriber: hiraditya.
Herald added a project: LLVM.

Delete temporarily constructed node uses for analysis after it's use,
holding onto original input nodes. Ideally this would be rewritten
without making nodes, but this appears relatively complex.


Repository:
  rL LLVM

https://reviews.llvm.org/D57921

Files:
  llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  llvm/test/CodeGen/X86/xor.ll


Index: llvm/test/CodeGen/X86/xor.ll
===================================================================
--- llvm/test/CodeGen/X86/xor.ll
+++ llvm/test/CodeGen/X86/xor.ll
@@ -419,15 +419,14 @@
 ;
 ; X64-LIN-LABEL: PR17487:
 ; X64-LIN:       # %bb.0:
-; X64-LIN-NEXT:    movd %edi, %xmm0
-; X64-LIN-NEXT:    pextrw $0, %xmm0, %eax
+; X64-LIN-NEXT:    movl %edi, %eax
 ; X64-LIN-NEXT:    andl $1, %eax
 ; X64-LIN-NEXT:    retq
 ;
 ; X64-WIN-LABEL: PR17487:
 ; X64-WIN:       # %bb.0:
-; X64-WIN-NEXT:    andb $1, %cl
 ; X64-WIN-NEXT:    movzbl %cl, %eax
+; X64-WIN-NEXT:    andl $1, %eax
 ; X64-WIN-NEXT:    retq
   %tmp = insertelement <2 x i1> undef, i1 %tobool, i32 1
   %tmp1 = zext <2 x i1> %tmp to <2 x i64>
Index: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -18675,12 +18675,17 @@
   // Determine if the condition we're dealing with is constant.
   SDValue SCC = SimplifySetCC(getSetCCResultType(CmpOpVT), N0, N1, CC, DL,
                               false);
-  if (SCC.getNode()) AddToWorklist(SCC.getNode());
-
-  if (auto *SCCC = dyn_cast_or_null<ConstantSDNode>(SCC.getNode())) {
-    // fold select_cc true, x, y -> x
-    // fold select_cc false, x, y -> y
-    return !SCCC->isNullValue() ? N2 : N3;
+  if (SCC.getNode()) {
+    if (auto *SCCC = dyn_cast<ConstantSDNode>(SCC.getNode())) {
+      // fold select_cc true, x, y -> x
+      // fold select_cc false, x, y -> y
+      bool isNull = SCCC->isNullValue();
+      SDValue RV = isNull ? N3 : N2;
+      return RV;
+    }
+    // Don't combine. Cleanup SCC. Don't remove input values.
+    HandleSDNode HN0(N0), HN1(N1), HN2(N2), HN3(N3);
+    recursivelyDeleteUnusedNodes(SCC.getNode());
   }
 
   if (SDValue V =


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