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[SelectionDAG] Check any use of negation result before removal

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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
This commit is contained in:
Qiu Chaofan
2020-09-17 16:00:54 +08:00
parent b05629230e
commit a2fb5446be
2 changed files with 43 additions and 7 deletions
Download Patch File Download Diff File Expand all files Collapse all files

22
llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
View File

@@ -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;

28
llvm/test/CodeGen/X86/pr47517.ll Normal file
View File

@@ -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
}