[IR][SDAG] Remove lifetime size handling from SDAG (#150944)

nikic · web-flow · commit ab1f6ce48248 · 2025-07-29T09:53:59.000+02:00
Split out from #150248: Specify that the argument of lifetime.start/lifetime.end is ignored and will be removed in the future. Remove lifetime size handling from SDAG. The size was previously discarded during isel, so was always ignored for stack coloring anyway. Where necessary, obtain the size of the full frame index.
diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst
@@ -26653,9 +26653,10 @@ object's lifetime.
 Arguments:
 """"""""""
 
-The first argument is a constant integer representing the size of the
-object, or -1 if it is variable sized. The second argument is a pointer
-to an ``alloca`` instruction.
+The first argument is a constant integer, which is ignored and will be removed
+in the future.
+
+The second argument is a pointer to an ``alloca`` instruction.
 
 Semantics:
 """"""""""
@@ -26693,9 +26694,10 @@ The '``llvm.lifetime.end``' intrinsic specifies the end of a
 Arguments:
 """"""""""
 
-The first argument is a constant integer representing the size of the
-object, or -1 if it is variable sized. The second argument is a pointer
-to an ``alloca`` instruction.
+The first argument is a constant integer, which is ignored and will be removed
+in the future.
+
+The second argument is a pointer to an ``alloca`` instruction.
 
 Semantics:
 """"""""""
diff --git a/llvm/include/llvm/CodeGen/SelectionDAG.h b/llvm/include/llvm/CodeGen/SelectionDAG.h
@@ -1428,10 +1428,9 @@ class SelectionDAG {
                                        EVT MemVT, MachineMemOperand *MMO);
 
   /// Creates a LifetimeSDNode that starts (`IsStart==true`) or ends
-  /// (`IsStart==false`) the lifetime of the portion of `FrameIndex` between
-  /// offsets `0` and `Size`.
+  /// (`IsStart==false`) the lifetime of the `FrameIndex`.
   LLVM_ABI SDValue getLifetimeNode(bool IsStart, const SDLoc &dl, SDValue Chain,
-                                   int FrameIndex, int64_t Size);
+                                   int FrameIndex);
 
   /// Creates a PseudoProbeSDNode with function GUID `Guid` and
   /// the index of the block `Index` it is probing, as well as the attributes
diff --git a/llvm/include/llvm/CodeGen/SelectionDAGNodes.h b/llvm/include/llvm/CodeGen/SelectionDAGNodes.h
@@ -1999,23 +1999,19 @@ class FrameIndexSDNode : public SDNode {
   }
 };
 
-/// This SDNode is used for LIFETIME_START/LIFETIME_END values, which indicate
-/// the offet and size that are started/ended in the underlying FrameIndex.
+/// This SDNode is used for LIFETIME_START/LIFETIME_END values.
 class LifetimeSDNode : public SDNode {
   friend class SelectionDAG;
-  int64_t Size;
 
   LifetimeSDNode(unsigned Opcode, unsigned Order, const DebugLoc &dl,
-                 SDVTList VTs, int64_t Size)
-      : SDNode(Opcode, Order, dl, VTs), Size(Size) {}
+                 SDVTList VTs)
+      : SDNode(Opcode, Order, dl, VTs) {}
 
 public:
   int64_t getFrameIndex() const {
     return cast<FrameIndexSDNode>(getOperand(1))->getIndex();
   }
 
-  int64_t getSize() const { return Size; }
-
   // Methods to support isa and dyn_cast
   static bool classof(const SDNode *N) {
     return N->getOpcode() == ISD::LIFETIME_START ||
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -35,6 +35,7 @@
 #include "llvm/CodeGen/ByteProvider.h"
 #include "llvm/CodeGen/DAGCombine.h"
 #include "llvm/CodeGen/ISDOpcodes.h"
+#include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/MachineMemOperand.h"
 #include "llvm/CodeGen/SDPatternMatch.h"
@@ -22778,8 +22779,10 @@ SDValue DAGCombiner::visitLIFETIME_END(SDNode *N) {
       const BaseIndexOffset StoreBase = BaseIndexOffset::match(ST, DAG);
       // If we store purely within object bounds just before its lifetime ends,
       // we can remove the store.
-      if (LifetimeEndBase.contains(DAG, LifetimeEnd->getSize() * 8, StoreBase,
-                                   StoreSize.getFixedValue() * 8)) {
+      MachineFrameInfo &MFI = DAG.getMachineFunction().getFrameInfo();
+      if (LifetimeEndBase.contains(
+              DAG, MFI.getObjectSize(LifetimeEnd->getFrameIndex()) * 8,
+              StoreBase, StoreSize.getFixedValue() * 8)) {
         LLVM_DEBUG(dbgs() << "\nRemoving store:"; StoreBase.dump();
                    dbgs() << "\nwithin LIFETIME_END of : ";
                    LifetimeEndBase.dump(); dbgs() << "\n");
@@ -29415,7 +29418,7 @@ bool DAGCombiner::mayAlias(SDNode *Op0, SDNode *Op1) const {
     MachineMemOperand *MMO;
   };
 
-  auto getCharacteristics = [](SDNode *N) -> MemUseCharacteristics {
+  auto getCharacteristics = [this](SDNode *N) -> MemUseCharacteristics {
     if (const auto *LSN = dyn_cast<LSBaseSDNode>(N)) {
       int64_t Offset = 0;
       if (auto *C = dyn_cast<ConstantSDNode>(LSN->getOffset()))
@@ -29428,13 +29431,15 @@ bool DAGCombiner::mayAlias(SDNode *Op0, SDNode *Op1) const {
               LSN->getBasePtr(),           Offset /*base offset*/,
               LocationSize::precise(Size), LSN->getMemOperand()};
     }
-    if (const auto *LN = cast<LifetimeSDNode>(N))
+    if (const auto *LN = cast<LifetimeSDNode>(N)) {
+      MachineFrameInfo &MFI = DAG.getMachineFunction().getFrameInfo();
       return {false /*isVolatile*/,
               /*isAtomic*/ false,
               LN->getOperand(1),
               0,
-              LocationSize::precise(LN->getSize()),
+              LocationSize::precise(MFI.getObjectSize(LN->getFrameIndex())),
               (MachineMemOperand *)nullptr};
+    }
     // Default.
     return {false /*isvolatile*/,
             /*isAtomic*/ false,
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -784,10 +784,6 @@ static void AddNodeIDCustom(FoldingSetNodeID &ID, const SDNode *N) {
   case ISD::TargetFrameIndex:
     ID.AddInteger(cast<FrameIndexSDNode>(N)->getIndex());
     break;
-  case ISD::LIFETIME_START:
-  case ISD::LIFETIME_END:
-    ID.AddInteger(cast<LifetimeSDNode>(N)->getSize());
-    break;
   case ISD::PSEUDO_PROBE:
     ID.AddInteger(cast<PseudoProbeSDNode>(N)->getGuid());
     ID.AddInteger(cast<PseudoProbeSDNode>(N)->getIndex());
@@ -9360,8 +9356,7 @@ SDValue SelectionDAG::getMemIntrinsicNode(unsigned Opcode, const SDLoc &dl,
 }
 
 SDValue SelectionDAG::getLifetimeNode(bool IsStart, const SDLoc &dl,
-                                      SDValue Chain, int FrameIndex,
-                                      int64_t Size) {
+                                      SDValue Chain, int FrameIndex) {
   const unsigned Opcode = IsStart ? ISD::LIFETIME_START : ISD::LIFETIME_END;
   const auto VTs = getVTList(MVT::Other);
   SDValue Ops[2] = {
@@ -9373,13 +9368,12 @@ SDValue SelectionDAG::getLifetimeNode(bool IsStart, const SDLoc &dl,
   FoldingSetNodeID ID;
   AddNodeIDNode(ID, Opcode, VTs, Ops);
   ID.AddInteger(FrameIndex);
-  ID.AddInteger(Size);
   void *IP = nullptr;
   if (SDNode *E = FindNodeOrInsertPos(ID, dl, IP))
     return SDValue(E, 0);
 
-  LifetimeSDNode *N = newSDNode<LifetimeSDNode>(Opcode, dl.getIROrder(),
-                                                dl.getDebugLoc(), VTs, Size);
+  LifetimeSDNode *N =
+      newSDNode<LifetimeSDNode>(Opcode, dl.getIROrder(), dl.getDebugLoc(), VTs);
   createOperands(N, Ops);
   CSEMap.InsertNode(N, IP);
   InsertNode(N);
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -7598,8 +7598,6 @@ void SelectionDAGBuilder::visitIntrinsicCall(const CallInst &I,
     if (TM.getOptLevel() == CodeGenOptLevel::None)
       return;
 
-    const int64_t ObjectSize =
-        cast<ConstantInt>(I.getArgOperand(0))->getSExtValue();
     const AllocaInst *LifetimeObject = cast<AllocaInst>(I.getArgOperand(1));
 
     // First check that the Alloca is static, otherwise it won't have a
@@ -7609,7 +7607,7 @@ void SelectionDAGBuilder::visitIntrinsicCall(const CallInst &I,
       return;
 
     const int FrameIndex = SI->second;
-    Res = DAG.getLifetimeNode(IsStart, sdl, getRoot(), FrameIndex, ObjectSize);
+    Res = DAG.getLifetimeNode(IsStart, sdl, getRoot(), FrameIndex);
     DAG.setRoot(Res);
     return;
   }
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGDumper.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGDumper.cpp
@@ -946,8 +946,6 @@ void SDNode::print_details(raw_ostream &OS, const SelectionDAG *G) const {
        << " -> "
        << ASC->getDestAddressSpace()
        << ']';
-  } else if (const LifetimeSDNode *LN = dyn_cast<LifetimeSDNode>(this)) {
-    OS << "<0 to " << LN->getSize() << ">";
   } else if (const auto *AA = dyn_cast<AssertAlignSDNode>(this)) {
     OS << '<' << AA->getAlign().value() << '>';
   }
diff --git a/llvm/test/CodeGen/X86/swap.ll b/llvm/test/CodeGen/X86/swap.ll
@@ -113,21 +113,17 @@ define dso_local void @onealloc_readback_1(ptr nocapture %a, ptr nocapture %b) l
 ;
 ; AA-LABEL: onealloc_readback_1:
 ; AA:       # %bb.0: # %entry
-; AA-NEXT:    vmovups (%rdi), %xmm0
-; AA-NEXT:    vmovaps %xmm0, -{{[0-9]+}}(%rsp)
 ; AA-NEXT:    vmovups (%rsi), %xmm0
 ; AA-NEXT:    vmovups %xmm0, (%rdi)
 ; AA-NEXT:    retq
 entry:
   %alloc = alloca [16 x i8], i8 2, align 1
   %part1 = getelementptr inbounds [16 x i8], ptr %alloc, i64 1, i64 0
-  call void @llvm.lifetime.start.p0(i64 16, ptr nonnull %part1)
-  call void @llvm.lifetime.start.p0(i64 16, ptr nonnull %alloc)
+  call void @llvm.lifetime.start.p0(i64 32, ptr nonnull %alloc)
   call void @llvm.memcpy.p0.p0.i64(ptr nonnull align 1 %part1, ptr align 1 %a, i64 16, i1 false)
   call void @llvm.memcpy.p0.p0.i64(ptr nonnull align 1 %alloc, ptr align 1 %b, i64 16, i1 false)
-  call void @llvm.lifetime.end.p0(i64 16, ptr nonnull %part1)
   tail call void @llvm.memcpy.p0.p0.i64(ptr nonnull align 1 %a, ptr align 1 %alloc, i64 16, i1 false)
-  call void @llvm.lifetime.end.p0(i64 16, ptr nonnull %alloc)
+  call void @llvm.lifetime.end.p0(i64 32, ptr nonnull %alloc)
   ret void
 }
 
@@ -144,19 +140,16 @@ define dso_local void @onealloc_readback_2(ptr nocapture %a, ptr nocapture %b) l
 ; 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
   %part2 = getelementptr inbounds [16 x i8], ptr %alloc, i64 1, i64 0
-  call void @llvm.lifetime.start.p0(i64 16, ptr nonnull %alloc)
-  call void @llvm.lifetime.start.p0(i64 16, ptr nonnull %part2)
+  call void @llvm.lifetime.start.p0(i64 32, ptr nonnull %alloc)
   call void @llvm.memcpy.p0.p0.i64(ptr nonnull align 1 %alloc, ptr align 1 %a, i64 16, i1 false)
   call void @llvm.memcpy.p0.p0.i64(ptr nonnull align 1 %part2, ptr align 1 %b, i64 16, i1 false)
-  call void @llvm.lifetime.end.p0(i64 16, ptr nonnull %alloc)
   tail call void @llvm.memcpy.p0.p0.i64(ptr nonnull align 1 %a, ptr align 1 %part2, i64 16, i1 false)
-  call void @llvm.lifetime.end.p0(i64 16, ptr nonnull %part2)
+  call void @llvm.lifetime.end.p0(i64 32, ptr nonnull %alloc)
   ret void
 }
 

Original file line number	Diff line number	Diff line change
`@@ -946,8 +946,6 @@ void SDNode::print_details(raw_ostream &OS, const SelectionDAG *G) const {`
`946`	`946`	`<< " -> "`
`947`	`947`	`<< ASC->getDestAddressSpace()`
`948`	`948`	`<< ']';`
`949`		`- } else if (const LifetimeSDNode *LN = dyn_cast<LifetimeSDNode>(this)) {`
`950`		`- OS << "<0 to " << LN->getSize() << ">";`
`951`	`949`	`} else if (const auto *AA = dyn_cast<AssertAlignSDNode>(this)) {`
`952`	`950`	`OS << '<' << AA->getAlign().value() << '>';`
`953`	`951`	`}`