[bpf] Do not expand UNDEF SDNode during insn selection lowering

o Before this patch, BPF backend will expand UNDEF node
    to i64 constant 0.
  o For second pass of dag combiner, legalizer will run through
    each to-be-processed dag node.
  o If any new SDNode is generated and has an undef operand,
    dag combiner will put undef node, newly-generated constant-0 node,
    and any node which uses these nodes in the working list.
  o During this process, it is possible undef operand is
    generated again, and this will form an infinite loop
    for dag combiner pass2.
  o This patch allows UNDEF to be a legal type.

Signed-off-by: Yonghong Song <yhs@plumgrid.com>
Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@249718 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/BPF/BPFISelDAGToDAG.cpp

@@ -130,13 +130,6 @@ SDNode *BPFDAGToDAGISel::Select(SDNode *Node) {
   // tablegen selection should be handled here.
   switch (Opcode) {
   default: break;
-
-  case ISD::UNDEF: {
-    errs() << "BUG: "; Node->dump(CurDAG); errs() << '\n';
-    report_fatal_error("shouldn't see UNDEF during Select");
-    break;
-  }
-
   case ISD::INTRINSIC_W_CHAIN: {
     unsigned IntNo = cast<ConstantSDNode>(Node->getOperand(1))->getZExtValue();
     switch (IntNo) {

lib/Target/BPF/BPFISelLowering.cpp

@@ -129,9 +129,6 @@ BPFTargetLowering::BPFTargetLowering(const TargetMachine &TM,
   setOperationAction(ISD::SUBC, MVT::i64, Expand);
   setOperationAction(ISD::SUBE, MVT::i64, Expand);
 
-  // no UNDEF allowed
-  setOperationAction(ISD::UNDEF, MVT::i64, Expand);
-
   setOperationAction(ISD::ROTR, MVT::i64, Expand);
   setOperationAction(ISD::ROTL, MVT::i64, Expand);
   setOperationAction(ISD::SHL_PARTS, MVT::i64, Expand);

test/CodeGen/BPF/sockex2.ll

@@ -311,7 +311,7 @@ flow_dissector.exit.thread:                       ; preds = %86, %12, %196, %199
 ; CHECK-LABEL: bpf_prog2:
 ; CHECK: ldabs_h r0, r6.data + 12 # encoding: [0x28,0x00,0x00,0x00,0x0c,0x00,0x00,0x00]
 ; CHECK: ldabs_h r0, r6.data + 16 # encoding: [0x28,0x00,0x00,0x00,0x10,0x00,0x00,0x00]
-; CHECK-NOT: implicit
+; CHECK: implicit-def: R1
 ; CHECK: ld_64   r1
 ; CHECK-NOT: ori
 ; CHECK: call 1 # encoding: [0x85,0x00,0x00,0x00,0x01,0x00,0x00,0x00]

test/CodeGen/BPF/undef.ll

@@ -0,0 +1,68 @@
+; RUN: llc < %s -march=bpf | FileCheck %s
+
+%struct.bpf_map_def = type { i32, i32, i32, i32 }
+%struct.__sk_buff = type opaque
+%struct.routing_key_2 = type { [6 x i8] }
+
+@routing = global %struct.bpf_map_def { i32 1, i32 6, i32 12, i32 1024 }, section "maps", align 4
+@routing_miss_0 = global %struct.bpf_map_def { i32 1, i32 1, i32 12, i32 1 }, section "maps", align 4
+@test1 = global %struct.bpf_map_def { i32 2, i32 4, i32 8, i32 1024 }, section "maps", align 4
+@test1_miss_4 = global %struct.bpf_map_def { i32 2, i32 1, i32 8, i32 1 }, section "maps", align 4
+@_license = global [4 x i8] c"GPL\00", section "license", align 1
+@llvm.used = appending global [6 x i8*] [i8* getelementptr inbounds ([4 x i8], [4 x i8]* @_license, i32 0, i32 0), i8* bitcast (i32 (%struct.__sk_buff*)* @ebpf_filter to i8*), i8* bitcast (%struct.bpf_map_def* @routing to i8*), i8* bitcast (%struct.bpf_map_def* @routing_miss_0 to i8*), i8* bitcast (%struct.bpf_map_def* @test1 to i8*), i8* bitcast (%struct.bpf_map_def* @test1_miss_4 to i8*)], section "llvm.metadata"
+
+; Function Attrs: nounwind uwtable
+define i32 @ebpf_filter(%struct.__sk_buff* nocapture readnone %ebpf_packet) #0 section "socket1" {
+  %key = alloca %struct.routing_key_2, align 1
+  %1 = getelementptr inbounds %struct.routing_key_2, %struct.routing_key_2* %key, i64 0, i32 0, i64 0
+; CHECK: mov	r1, 5
+; CHECK: stb	-8(r10), r1
+  store i8 5, i8* %1, align 1
+  %2 = getelementptr inbounds %struct.routing_key_2, %struct.routing_key_2* %key, i64 0, i32 0, i64 1
+; CHECK: mov	r1, 6
+; CHECK: stb	-7(r10), r1
+  store i8 6, i8* %2, align 1
+  %3 = getelementptr inbounds %struct.routing_key_2, %struct.routing_key_2* %key, i64 0, i32 0, i64 2
+; CHECK: mov	r1, 7
+; CHECK: stb	-6(r10), r1
+  store i8 7, i8* %3, align 1
+  %4 = getelementptr inbounds %struct.routing_key_2, %struct.routing_key_2* %key, i64 0, i32 0, i64 3
+; CHECK: mov	r1, 8
+; CHECK: stb	-5(r10), r1
+  store i8 8, i8* %4, align 1
+  %5 = getelementptr inbounds %struct.routing_key_2, %struct.routing_key_2* %key, i64 0, i32 0, i64 4
+; CHECK: mov	r1, 9
+; CHECK: stb	-4(r10), r1
+  store i8 9, i8* %5, align 1
+  %6 = getelementptr inbounds %struct.routing_key_2, %struct.routing_key_2* %key, i64 0, i32 0, i64 5
+; CHECK: mov	r1, 10
+; CHECK: stb	-3(r10), r1
+  store i8 10, i8* %6, align 1
+  %7 = getelementptr inbounds %struct.routing_key_2, %struct.routing_key_2* %key, i64 1, i32 0, i64 0
+; CHECK: mov	r1, r10
+; CHECK: addi	r1, -2
+; CHECK: mov	r2, 0
+; CHECK: sth	6(r1), r2
+; CHECK: sth	4(r1), r2
+; CHECK: sth	2(r1), r2
+; CHECK: sth	24(r10), r2
+; CHECK: sth	22(r10), r2
+; CHECK: sth	20(r10), r2
+; CHECK: sth	18(r10), r2
+; CHECK: sth	16(r10), r2
+; CHECK: sth	14(r10), r2
+; CHECK: sth	12(r10), r2
+; CHECK: sth	10(r10), r2
+; CHECK: sth	8(r10), r2
+; CHECK: sth	6(r10), r2
+; CHECK: sth	-2(r10), r2
+; CHECK: sth	26(r10), r2
+  call void @llvm.memset.p0i8.i64(i8* %7, i8 0, i64 30, i32 1, i1 false)
+  %8 = call i32 (%struct.bpf_map_def*, %struct.routing_key_2*, ...) bitcast (i32 (...)* @bpf_map_lookup_elem to i32 (%struct.bpf_map_def*, %struct.routing_key_2*, ...)*)(%struct.bpf_map_def* nonnull @routing, %struct.routing_key_2* nonnull %key) #3
+  ret i32 undef
+}
+
+; Function Attrs: nounwind argmemonly
+declare void @llvm.memset.p0i8.i64(i8* nocapture, i8, i64, i32, i1) #1
+
+declare i32 @bpf_map_lookup_elem(...) #2