[llvm] a2fb544 - [SelectionDAG] Check any use of negation result before removal

[Qiu Chaofan via llvm-commits]

Author: Qiu Chaofan
Date: 2020-09-17T16:00:54+08:00
New Revision: a2fb5446be960ad164060b3c05fc268f7f72d67a

URL: https://github.com/llvm/llvm-project/commit/a2fb5446be960ad164060b3c05fc268f7f72d67a
DIFF: https://github.com/llvm/llvm-project/commit/a2fb5446be960ad164060b3c05fc268f7f72d67a.diff

LOG: [SelectionDAG] Check any use of negation result before removal

2508ef01 fixed a bug about constant removal in negation. But after
sanitizing check I found there's still some issue about it so it's
reverted.

Temporary nodes will be removed if useless in negation. Before the
removal, they'd be checked if any other nodes used it. So the removal
was moved after getNode. However in rare cases the node to be removed is
the same as result of getNode. We missed that and will be fixed by this
patch.

Reviewed By: steven.zhang

Differential Revision: https://reviews.llvm.org/D87614

Added: 
    llvm/test/CodeGen/X86/pr47517.ll

Modified: 
    llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index 3446ee0efc45..5c9273150014 100644
--- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -5773,8 +5773,10 @@ SDValue TargetLowering::getNegatedExpression(SDValue Op, SelectionDAG &DAG,
 
     // If we already have the use of the negated floating constant, it is free
     // to negate it even it has multiple uses.
-    if (!Op.hasOneUse() && CFP.use_empty())
+    if (!Op.hasOneUse() && CFP.use_empty()) {
+      RemoveDeadNode(CFP);
       break;
+    }
     Cost = NegatibleCost::Neutral;
     return CFP;
   }
@@ -5832,7 +5834,8 @@ SDValue TargetLowering::getNegatedExpression(SDValue Op, SelectionDAG &DAG,
     if (NegX && (CostX <= CostY)) {
       Cost = CostX;
       SDValue N = DAG.getNode(ISD::FSUB, DL, VT, NegX, Y, Flags);
-      RemoveDeadNode(NegY);
+      if (NegY != N)
+        RemoveDeadNode(NegY);
       return N;
     }
 
@@ -5840,7 +5843,8 @@ SDValue TargetLowering::getNegatedExpression(SDValue Op, SelectionDAG &DAG,
     if (NegY) {
       Cost = CostY;
       SDValue N = DAG.getNode(ISD::FSUB, DL, VT, NegY, X, Flags);
-      RemoveDeadNode(NegX);
+      if (NegX != N)
+        RemoveDeadNode(NegX);
       return N;
     }
     break;
@@ -5879,7 +5883,8 @@ SDValue TargetLowering::getNegatedExpression(SDValue Op, SelectionDAG &DAG,
     if (NegX && (CostX <= CostY)) {
       Cost = CostX;
       SDValue N = DAG.getNode(Opcode, DL, VT, NegX, Y, Flags);
-      RemoveDeadNode(NegY);
+      if (NegY != N)
+        RemoveDeadNode(NegY);
       return N;
     }
 
@@ -5892,7 +5897,8 @@ SDValue TargetLowering::getNegatedExpression(SDValue Op, SelectionDAG &DAG,
     if (NegY) {
       Cost = CostY;
       SDValue N = DAG.getNode(Opcode, DL, VT, X, NegY, Flags);
-      RemoveDeadNode(NegX);
+      if (NegX != N)
+        RemoveDeadNode(NegX);
       return N;
     }
     break;
@@ -5923,7 +5929,8 @@ SDValue TargetLowering::getNegatedExpression(SDValue Op, SelectionDAG &DAG,
     if (NegX && (CostX <= CostY)) {
       Cost = std::min(CostX, CostZ);
       SDValue N = DAG.getNode(Opcode, DL, VT, NegX, Y, NegZ, Flags);
-      RemoveDeadNode(NegY);
+      if (NegY != N)
+        RemoveDeadNode(NegY);
       return N;
     }
 
@@ -5931,7 +5938,8 @@ SDValue TargetLowering::getNegatedExpression(SDValue Op, SelectionDAG &DAG,
     if (NegY) {
       Cost = std::min(CostY, CostZ);
       SDValue N = DAG.getNode(Opcode, DL, VT, X, NegY, NegZ, Flags);
-      RemoveDeadNode(NegX);
+      if (NegX != N)
+        RemoveDeadNode(NegX);
       return N;
     }
     break;

diff  --git a/llvm/test/CodeGen/X86/pr47517.ll b/llvm/test/CodeGen/X86/pr47517.ll
new file mode 100644
index 000000000000..5672fbc69a41
--- /dev/null
+++ b/llvm/test/CodeGen/X86/pr47517.ll
@@ -0,0 +1,28 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple x86_64 < %s | FileCheck %s
+
+; To ensure unused floating point constant is correctly removed
+define float @test(float %src, float* %p) {
+; CHECK-LABEL: test:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    movq $0, (%rdi)
+; CHECK-NEXT:    xorps %xmm0, %xmm0
+; CHECK-NEXT:    retq
+entry:
+  %a0 = getelementptr inbounds float, float* %p, i32 0
+  %a1 = getelementptr inbounds float, float* %p, i32 1
+  store float 0.000000e+00, float* %a0
+  store float 0.000000e+00, float* %a1
+  %zero = load float, float* %a0
+  %fmul1 = fmul fast float %zero, %src
+  %fadd1 = fadd fast float %fmul1, %zero
+  %fmul2 = fmul fast float %fadd1, 2.000000e+00
+  %fmul3 = fmul fast float %fmul2, %fmul2
+  %fmul4 = fmul fast float %fmul2, 2.000000e+00
+  %fadd2 = fadd fast float %fmul4, -3.000000e+00
+  %fmul5 = fmul fast float %fadd2, %fmul2
+  %fadd3 = fadd fast float %fmul2, %src
+  %fadd4 = fadd fast float %fadd3, %fmul5
+  %fmul6 = fmul fast float %fmul3, %fadd4
+  ret float %fmul6
+}