Revert "[DAGCombine] Improve Lifetime node chains." and follow-ups

[inglorion]

Summary

This reverts r357309 and r357256.

Reason for revert: r357256 causes pathologically slow DAG Combining 1
times on some inputs (PR41352). r357309 builds on r357256 and so is
also reverted here.

[rnk]

lgtm

In the future, it's not necessary to ask for code review to commit a revert.

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

private:
     SDValue visitBRCOND(SDNode *N);
     SDValue visitBR_CC(SDNode *N);
     SDValue visitLOAD(SDNode *N);
 
     SDValue replaceStoreChain(StoreSDNode *ST, SDValue BetterChain);
     SDValue replaceStoreOfFPConstant(StoreSDNode *ST);
 
     SDValue visitSTORE(SDNode *N);
-
-    SDValue ImproveLifetimeNodeChain(SDNode *N);
-
-    SDValue visitLIFETIME_START(SDNode *N);
     SDValue visitLIFETIME_END(SDNode *N);
     SDValue visitINSERT_VECTOR_ELT(SDNode *N);
     SDValue visitEXTRACT_VECTOR_ELT(SDNode *N);
     SDValue visitBUILD_VECTOR(SDNode *N);
     SDValue visitCONCAT_VECTORS(SDNode *N);
     SDValue visitEXTRACT_SUBVECTOR(SDNode *N);
     SDValue visitVECTOR_SHUFFLE(SDNode *N);
     SDValue visitSCALAR_TO_VECTOR(SDNode *N);
SDValue DAGCombiner::visit(SDNode *N) {
   case ISD::EXTRACT_SUBVECTOR:  return visitEXTRACT_SUBVECTOR(N);
   case ISD::VECTOR_SHUFFLE:     return visitVECTOR_SHUFFLE(N);
   case ISD::SCALAR_TO_VECTOR:   return visitSCALAR_TO_VECTOR(N);
   case ISD::INSERT_SUBVECTOR:   return visitINSERT_SUBVECTOR(N);
   case ISD::MGATHER:            return visitMGATHER(N);
   case ISD::MLOAD:              return visitMLOAD(N);
   case ISD::MSCATTER:           return visitMSCATTER(N);
   case ISD::MSTORE:             return visitMSTORE(N);
-  case ISD::LIFETIME_START:     return visitLIFETIME_START(N);
   case ISD::LIFETIME_END:       return visitLIFETIME_END(N);
   case ISD::FP_TO_FP16:         return visitFP_TO_FP16(N);
   case ISD::FP16_TO_FP:         return visitFP16_TO_FP(N);
   case ISD::VECREDUCE_FADD:
   case ISD::VECREDUCE_FMUL:
   case ISD::VECREDUCE_ADD:
   case ISD::VECREDUCE_MUL:
   case ISD::VECREDUCE_AND:
SDValue DAGCombiner::visitSTORE(SDNode *N) {
   }
 
   if (SDValue NewSt = splitMergedValStore(ST))
     return NewSt;
 
   return ReduceLoadOpStoreWidth(N);
 }
 
-SDValue DAGCombiner::ImproveLifetimeNodeChain(SDNode *N) {
-  auto Chain = N->getOperand(0);
-  auto NewChain = FindBetterChain(N, Chain);
-  if (NewChain != Chain) {
-    LifetimeSDNode *LN = cast<LifetimeSDNode>(N);
-    // Create New Node to prevent loop in CombineTo.
-    SDValue NewN = DAG.getLifetimeNode(N->getOpcode() == ISD::LIFETIME_START,
-                                       SDLoc(N), NewChain, LN->getFrameIndex(),
-                                       LN->hasOffset() ? LN->getSize() : -1,
-                                       LN->hasOffset() ? LN->getOffset() : -1);
-    AddToWorklist(NewN.getNode());
-    auto TF = DAG.getNode(ISD::TokenFactor, SDLoc(N), MVT::Other, Chain, NewN);
-    return CombineTo(N, TF);
-  }
-  return SDValue();
-}
-
-SDValue DAGCombiner::visitLIFETIME_START(SDNode *N) {
-  if (SDValue V = ImproveLifetimeNodeChain(N))
-    return V;
-  return SDValue();
-}
-
 SDValue DAGCombiner::visitLIFETIME_END(SDNode *N) {
-  if (SDValue V = ImproveLifetimeNodeChain(N))
-    return V;
-
   const auto *LifetimeEnd = cast<LifetimeSDNode>(N);
   if (!LifetimeEnd->hasOffset())
     return SDValue();
 
   const BaseIndexOffset LifetimeEndBase(N->getOperand(1), SDValue(),
                                         LifetimeEnd->getOffset(), false);
 
   // We walk up the chains to find stores.

llvm/test/CodeGen/X86/swap.ll

 ; NOAA-NEXT:    vmovups (%rdi), %xmm0
 ; NOAA-NEXT:    vmovaps %xmm0, -{{[0-9]+}}(%rsp)
 ; NOAA-NEXT:    vmovups %xmm0, (%rsi)
 ; NOAA-NEXT:    retq
 ;
 ; AA-LABEL: twoallocs:
 ; AA:       # %bb.0: # %entry
 ; AA-NEXT:    vmovups (%rdi), %xmm0
+; AA-NEXT:    vmovaps %xmm0, -{{[0-9]+}}(%rsp)
 ; AA-NEXT:    vmovups %xmm0, (%rsi)
 ; AA-NEXT:    retq
 entry:
   %alloc1 = alloca [16 x i8], align 1
   %alloc2 = alloca [16 x i8], align 1
   %part1 = getelementptr inbounds [16 x i8], [16 x i8]* %alloc1, i64 0, i64 0
   %part2 = getelementptr inbounds [16 x i8], [16 x i8]* %alloc2, i64 0, i64 0
   %part2_alias = getelementptr inbounds [16 x i8], [16 x i8]* %alloc2, i64 0, i64 0

 ; NOAA-NEXT:    vmovups (%rsi), %xmm0
 ; NOAA-NEXT:    vmovaps %xmm0, -{{[0-9]+}}(%rsp)
 ; NOAA-NEXT:    vmovups %xmm0, (%rdi)
 ; NOAA-NEXT:    retq
 ;
 ; AA-LABEL: onealloc_readback_1:
 ; AA:       # %bb.0: # %entry
 ; AA-NEXT:    vmovups (%rsi), %xmm0
+; AA-NEXT:    vmovaps %xmm0, -{{[0-9]+}}(%rsp)
 ; AA-NEXT:    vmovups %xmm0, (%rdi)
 ; AA-NEXT:    retq
 entry:
   %alloc = alloca [16 x i8], i8 2, align 1
   %part2 = getelementptr inbounds [16 x i8], [16 x i8]* %alloc, i64 0, i64 0
   %part1 = getelementptr inbounds [16 x i8], [16 x i8]* %alloc, i64 1, i64 0
   call void @llvm.lifetime.start.p0i8(i64 16, i8* nonnull %part1)
   call void @llvm.lifetime.start.p0i8(i64 16, i8* nonnull %part2)

 ; NOAA-NEXT:    vmovups (%rsi), %xmm0
 ; NOAA-NEXT:    vmovaps %xmm0, -{{[0-9]+}}(%rsp)
 ; NOAA-NEXT:    vmovups %xmm0, (%rdi)
 ; NOAA-NEXT:    retq
 ;
 ; AA-LABEL: onealloc_readback_2:
 ; AA:       # %bb.0: # %entry
 ; AA-NEXT:    vmovups (%rsi), %xmm0
+; AA-NEXT:    vmovaps %xmm0, -{{[0-9]+}}(%rsp)
 ; AA-NEXT:    vmovups %xmm0, (%rdi)
 ; AA-NEXT:    retq
 entry:
   %alloc = alloca [16 x i8], i8 2, align 1
   %part1 = getelementptr inbounds [16 x i8], [16 x i8]* %alloc, i64 0, i64 0
   %part2 = getelementptr inbounds [16 x i8], [16 x i8]* %alloc, i64 1, i64 0
   call void @llvm.lifetime.start.p0i8(i64 16, i8* nonnull %part1)
   call void @llvm.lifetime.start.p0i8(i64 16, i8* nonnull %part2)

llvm/test/DebugInfo/COFF/lexicalblock.ll

 ; CHECK: }
 ; CHECK: BlockSym {
 ; CHECK:   Kind: S_BLOCK32 {{.*}}
 ; CHECK:   BlockName: 
 ; CHECK: }
 ; CHECK: ScopeEndSym {
 ; CHECK:   Kind: S_END {{.*}}
 ; CHECK: }
+; CHECK: BlockSym {
+; CHECK:   Kind: S_BLOCK32 {{.*}}
+; CHECK:   BlockName: 
+; CHECK: }
+; CHECK: ScopeEndSym {
+; CHECK: }
+; CHECK: BlockSym {
+; CHECK:   Kind: S_BLOCK32 {{.*}}
+; CHECK:   BlockName: 
+; CHECK: }
+; CHECK: ScopeEndSym {
+; CHECK:   Kind: S_END {{.*}}
+; CHECK: }
 ; CHECK: ProcEnd {
 ; CHECK: }
 ;
 ; ModuleID = 'lexicalblock.cxx'
 source_filename = "lexicalblock.cxx"
 target datalayout = "e-m:x-p:32:32-i64:64-f80:32-n8:16:32-a:0:32-S32"
 target triple = "i686-pc-windows-msvc"