[PATCH] D113888: [SDAG] Use UnknownSize for masked load/store MMO size

[Dave Green via Phabricator via llvm-commits]

dmgreen created this revision.
dmgreen added reviewers: efriedma, craig.topper, SjoerdMeijer, RKSimon, nikic.
Herald added a subscriber: hiraditya.
dmgreen requested review of this revision.
Herald added a project: LLVM.

A masked load or store will load a potentially unknown size of bytes from a memory location - that is not generally known at compile time. They do not necessarily load/store the entire vector width, and treating them as such can lead to incorrect aliasing information (for example, if the underlying object is smaller than the size of the vector).

This makes sure that the MMO is given an unknown size to represent this. which is less accurate that "may load/store from up to 16 bytes", but less incorrect that "will load/store from 16 bytes".


https://reviews.llvm.org/D113888

Files:
  llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
  llvm/test/CodeGen/Thumb2/mve-masked-store-mmo.ll


Index: llvm/test/CodeGen/Thumb2/mve-masked-store-mmo.ll
===================================================================
--- llvm/test/CodeGen/Thumb2/mve-masked-store-mmo.ll
+++ llvm/test/CodeGen/Thumb2/mve-masked-store-mmo.ll
@@ -11,15 +11,15 @@
 ; CHECK-NEXT:    adr r0, .LCPI0_0
 ; CHECK-NEXT:    vldrw.u32 q0, [r0]
 ; CHECK-NEXT:    add.w r0, sp, #2
-; CHECK-NEXT:    ldrb.w r1, [sp, #3]
 ; CHECK-NEXT:    vpst
 ; CHECK-NEXT:    vstrbt.8 q0, [r0]
-; CHECK-NEXT:    ldrb.w r2, [sp, #4]
 ; CHECK-NEXT:    ldrb.w r0, [sp, #2]
-; CHECK-NEXT:    ldrb.w r3, [sp, #10]
+; CHECK-NEXT:    ldrb.w r1, [sp, #3]
+; CHECK-NEXT:    ldrb.w r2, [sp, #4]
 ; CHECK-NEXT:    add r0, r1
-; CHECK-NEXT:    ldrb.w r1, [sp, #11]
+; CHECK-NEXT:    ldrb.w r3, [sp, #10]
 ; CHECK-NEXT:    add r0, r2
+; CHECK-NEXT:    ldrb.w r1, [sp, #11]
 ; CHECK-NEXT:    add r0, r3
 ; CHECK-NEXT:    add r0, r1
 ; CHECK-NEXT:    add sp, #12
Index: llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
===================================================================
--- llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -4336,9 +4336,7 @@
 
   MachineMemOperand *MMO = DAG.getMachineFunction().getMachineMemOperand(
       MachinePointerInfo(PtrOperand), MachineMemOperand::MOStore,
-      // TODO: Make MachineMemOperands aware of scalable
-      // vectors.
-      VT.getStoreSize().getKnownMinSize(), *Alignment, I.getAAMetadata());
+      MemoryLocation::UnknownSize, *Alignment, I.getAAMetadata());
   SDValue StoreNode =
       DAG.getMaskedStore(getMemoryRoot(), sdl, Src0, Ptr, Offset, Mask, VT, MMO,
                          ISD::UNINDEXED, false /* Truncating */, IsCompressing);
@@ -4496,22 +4494,14 @@
   const MDNode *Ranges = I.getMetadata(LLVMContext::MD_range);
 
   // Do not serialize masked loads of constant memory with anything.
-  MemoryLocation ML;
-  if (VT.isScalableVector())
-    ML = MemoryLocation::getAfter(PtrOperand);
-  else
-    ML = MemoryLocation(PtrOperand, LocationSize::precise(
-                           DAG.getDataLayout().getTypeStoreSize(I.getType())),
-                           AAInfo);
+  MemoryLocation ML = MemoryLocation::getAfter(PtrOperand, AAInfo);
   bool AddToChain = !AA || !AA->pointsToConstantMemory(ML);
 
   SDValue InChain = AddToChain ? DAG.getRoot() : DAG.getEntryNode();
 
   MachineMemOperand *MMO = DAG.getMachineFunction().getMachineMemOperand(
       MachinePointerInfo(PtrOperand), MachineMemOperand::MOLoad,
-      // TODO: Make MachineMemOperands aware of scalable
-      // vectors.
-      VT.getStoreSize().getKnownMinSize(), *Alignment, AAInfo, Ranges);
+      MemoryLocation::UnknownSize, *Alignment, AAInfo, Ranges);
 
   SDValue Load =
       DAG.getMaskedLoad(VT, sdl, InChain, Ptr, Offset, Mask, Src0, VT, MMO,


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D113888.387228.patch
Type: text/x-patch
Size: 2829 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20211115/793239f5/attachment.bin>