[PATCH] D86689: [DAGCombine] Don't delete the node if it has uses immediately

[Qing Shan Zhang via Phabricator via llvm-commits]

steven.zhang created this revision.
steven.zhang added reviewers: spatel, hans, qiucf, RKSimon, PowerPC.
Herald added subscribers: ecnelises, hiraditya, nemanjai.
Herald added a project: LLVM.
steven.zhang requested review of this revision.

This is the follow up patch for https://reviews.llvm.org/D86183 as we miss to delete the node if NegX == NegY, which has use after we create the node.

  if (NegX && (CostX <= CostY)) {
    Cost = std::min(CostX, CostZ);
    if (NegX != NegY)
      RemoveDeadNode(NegY);
    return DAG.getNode(Opcode, DL, VT, NegX, Y, NegZ, Flags);  #<-- NegX is used here and we need to make sure that, NegY != NegX.
  }


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D86689

Files:
  llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
  llvm/test/CodeGen/PowerPC/fneg.ll


Index: llvm/test/CodeGen/PowerPC/fneg.ll
===================================================================
--- llvm/test/CodeGen/PowerPC/fneg.ll
+++ llvm/test/CodeGen/PowerPC/fneg.ll
@@ -39,3 +39,28 @@
   %r = call float @llvm.fmuladd.f32(float %negx, float %negy, float %z)
   ret float %r
 }
+
+; Verify that we didn't hit assertion for this case.
+define void @fneg_no_ice() {
+; CHECK-LABEL: fneg_no_ice:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    lfs f0, 0(r3)
+; CHECK-NEXT:    lis r3, .LCPI3_0 at ha
+; CHECK-NEXT:    lfs f1, .LCPI3_0 at l(r3)
+; CHECK-NEXT:    fsubs f0, f1, f0
+; CHECK-NEXT:    fmul f1, f0, f0
+; CHECK-NEXT:    fmul f0, f0, f1
+; CHECK-NEXT:    frsp f0, f0
+; CHECK-NEXT:    stfs f0, 0(r3)
+; CHECK-NEXT:    blr
+  %_val_rw_ = load float, float* undef, align 4
+  %_val_w_ = load float, float* undef, align 4
+  %_sub_tmp = fsub fast float 1.000000e+00, %_val_w_
+  %_conv25 = fpext float %_sub_tmp to double
+  %_expi_result = call fast double @llvm.powi.f64(double %_conv25, i32 3)
+  %_conv26 = fptrunc double %_expi_result to float
+  store float %_conv26, float* undef, align 4
+  ret void
+}
+
+declare double @llvm.powi.f64(double, i32)
Index: llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
===================================================================
--- llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -5820,14 +5820,16 @@
     // Negate the X if its cost is less or equal than Y.
     if (NegX && (CostX <= CostY)) {
       Cost = CostX;
-      RemoveDeadNode(NegY);
+      if (NegX != NegY)
+        RemoveDeadNode(NegY);
       return DAG.getNode(ISD::FSUB, DL, VT, NegX, Y, Flags);
     }
 
     // Negate the Y if it is not expensive.
     if (NegY) {
       Cost = CostY;
-      RemoveDeadNode(NegX);
+      if (NegX != NegY)
+        RemoveDeadNode(NegX);
       return DAG.getNode(ISD::FSUB, DL, VT, NegY, X, Flags);
     }
     break;
@@ -5865,7 +5867,8 @@
     // Negate the X if its cost is less or equal than Y.
     if (NegX && (CostX <= CostY)) {
       Cost = CostX;
-      RemoveDeadNode(NegY);
+      if (NegX != NegY)
+        RemoveDeadNode(NegY);
       return DAG.getNode(Opcode, DL, VT, NegX, Y, Flags);
     }
 
@@ -5877,7 +5880,8 @@
     // Negate the Y if it is not expensive.
     if (NegY) {
       Cost = CostY;
-      RemoveDeadNode(NegX);
+      if (NegX != NegY)
+        RemoveDeadNode(NegX);
       return DAG.getNode(Opcode, DL, VT, X, NegY, Flags);
     }
     break;
@@ -5907,14 +5911,16 @@
     // Negate the X if its cost is less or equal than Y.
     if (NegX && (CostX <= CostY)) {
       Cost = std::min(CostX, CostZ);
-      RemoveDeadNode(NegY);
+      if (NegX != NegY)
+        RemoveDeadNode(NegY);
       return DAG.getNode(Opcode, DL, VT, NegX, Y, NegZ, Flags);
     }
 
     // Negate the Y if it is not expensive.
     if (NegY) {
       Cost = std::min(CostY, CostZ);
-      RemoveDeadNode(NegX);
+      if (NegX != NegY)
+        RemoveDeadNode(NegX);
       return DAG.getNode(Opcode, DL, VT, X, NegY, NegZ, Flags);
     }
     break;


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