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Use the return value of UpdateNodeOperands(); in some cases, UpdateNodeOperands() modifies the node in-place and using the return value isn’t strictly necessary. However, it does not necessarily modify the node, but may return a resultant node if it already exists in the DAG. See comments in UpdateNodeOperands(). In that case, the return value must be used to avoid such scenarios as an infinite loop (node is assumed to have been updated, so added back to the worklist, and re-processed; however, node hasn’t changed so it is once again passed to UpdateNodeOperands(), assumed modified, added back to worklist; cycle infinitely repeats).

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Differential Revision: https://reviews.llvm.org/D38466

llvm-svn: 315957
This commit is contained in:
Mark Searles 2017-10-16 23:38:53 +00:00
parent e0d1abfff0
commit 67e40dbe69
3 changed files with 97 additions and 3 deletions
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2
lib/CodeGen/SelectionDAG/TargetLowering.cpp
View File

@ -469,7 +469,7 @@ TargetLowering::SimplifyDemandedBits(SDNode *User, unsigned OpIdx,
}
NewOps.push_back(User->getOperand(i));
}
TLO.DAG.UpdateNodeOperands(User, NewOps);
User = TLO.DAG.UpdateNodeOperands(User, NewOps);
// Op has less users now, so we may be able to perform additional combines
// with it.
DCI.AddToWorklist(Op.getNode());

3
lib/Target/AMDGPU/SIISelLowering.cpp
View File

@ -6507,8 +6507,7 @@ SDNode *SITargetLowering::legalizeTargetIndependentNode(SDNode *Node,
Node->getOperand(i)), 0));
}
DAG.UpdateNodeOperands(Node, Ops);
return Node;
return DAG.UpdateNodeOperands(Node, Ops);
}
/// \brief Fold the instructions after selecting them.

95
test/CodeGen/AMDGPU/simplifydemandedbits-recursion.ll Normal file
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@ -0,0 +1,95 @@
; RUN: llc -march=amdgcn < %s | FileCheck %s
; Check we can compile this bugpoint-reduced test without an
; infinite loop in TLI.SimplifyDemandedBits() due to failure
; to use return value of TLO.DAG.UpdateNodeOperands()
; Check that code was generated; we know there will be
; a s_endpgm, so check for it.
@0 = external unnamed_addr addrspace(3) global [462 x float], align 4
; Function Attrs: nounwind readnone speculatable
declare i32 @llvm.amdgcn.workitem.id.y() #0
; Function Attrs: nounwind readnone speculatable
declare i32 @llvm.amdgcn.workitem.id.x() #0
; Function Attrs: nounwind readnone speculatable
declare float @llvm.fmuladd.f32(float, float, float) #0
; CHECK: s_endpgm
define amdgpu_kernel void @foo(float addrspace(1)* noalias nocapture readonly %arg, float addrspace(1)* noalias nocapture readonly %arg1, float addrspace(1)* noalias nocapture %arg2, float %arg3) local_unnamed_addr !reqd_work_group_size !0 {
bb:
%tmp = tail call i32 @llvm.amdgcn.workitem.id.y()
%tmp4 = tail call i32 @llvm.amdgcn.workitem.id.x()
%tmp5 = and i32 %tmp, 15
%tmp6 = mul nuw nsw i32 %tmp5, 21
%tmp7 = sub i32 %tmp6, 0
%tmp8 = add i32 %tmp7, 0
%tmp9 = add i32 %tmp8, 0
%tmp10 = getelementptr inbounds [462 x float], [462 x float] addrspace(3)* @0, i32 0, i32 0
br label %bb12
bb11: ; preds = %bb30
br i1 undef, label %bb37, label %bb38
bb12: ; preds = %bb30, %bb
br i1 false, label %.preheader, label %.loopexit145
.loopexit145: ; preds = %.preheader, %bb12
br label %bb13
bb13: ; preds = %.loopexit, %.loopexit145
%tmp14 = phi i32 [ %tmp5, %.loopexit145 ], [ %tmp20, %.loopexit ]
%tmp15 = add nsw i32 %tmp14, -3
%tmp16 = mul i32 %tmp14, 21
br i1 undef, label %bb17, label %.loopexit
bb17: ; preds = %bb13
%tmp18 = mul i32 %tmp15, 224
%tmp19 = add i32 undef, %tmp18
br label %bb21
.loopexit: ; preds = %bb21, %bb13
%tmp20 = add nuw nsw i32 %tmp14, 16
br i1 undef, label %bb13, label %bb26
bb21: ; preds = %bb21, %bb17
%tmp22 = phi i32 [ %tmp4, %bb17 ], [ %tmp25, %bb21 ]
%tmp23 = add i32 %tmp22, %tmp16
%tmp24 = getelementptr inbounds float, float addrspace(3)* %tmp10, i32 %tmp23
store float undef, float addrspace(3)* %tmp24, align 4
%tmp25 = add nuw i32 %tmp22, 8
br i1 undef, label %bb21, label %.loopexit
bb26: ; preds = %.loopexit
br label %bb31
.preheader: ; preds = %.preheader, %bb12
%tmp27 = phi i32 [ %tmp28, %.preheader ], [ undef, %bb12 ]
%tmp28 = add nuw i32 %tmp27, 128
%tmp29 = icmp ult i32 %tmp28, 1568
br i1 %tmp29, label %.preheader, label %.loopexit145
bb30: ; preds = %bb31
br i1 undef, label %bb11, label %bb12
bb31: ; preds = %bb31, %bb26
%tmp32 = phi i32 [ %tmp9, %bb26 ], [ undef, %bb31 ]
%tmp33 = getelementptr inbounds [462 x float], [462 x float] addrspace(3)* @0, i32 0, i32 %tmp32
%tmp34 = load float, float addrspace(3)* %tmp33, align 4
%tmp35 = tail call float @llvm.fmuladd.f32(float %tmp34, float undef, float undef)
%tmp36 = tail call float @llvm.fmuladd.f32(float undef, float undef, float %tmp35)
br i1 undef, label %bb30, label %bb31
bb37: ; preds = %bb11
br label %bb38
bb38: ; preds = %bb37, %bb11
ret void
}
attributes #0 = { nounwind readnone speculatable }
!0 = !{i32 8, i32 16, i32 1}