[SelectionDAG] Remove pointer from MMO for VP strided load/store.

[topperc]

MachineIR alias analysis assumes that only bytes after the pointer will be accessed. This is incorrect if the stride is negative.

This is causing miscompiles in our downstream after SLP started making strided loads.

Fixes #82657

[llvmbot]

@llvm/pr-subscribers-llvm-selectiondag

Author: Craig Topper (topperc)

Changes

MachineIR alias analysis assumes that only bytes after the pointer will be accessed. This is incorrect if the stride is negative.

This is causing miscompiles in our downstream after SLP started making strided loads.

---

Full diff: https://github.com/llvm/llvm-project/pull/82667.diff

1 Files Affected:

• (modified) llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp (+4-2)

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index e893a5b616d33e..3e53f3318a374a 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -8017,8 +8017,9 @@ void SelectionDAGBuilder::visitVPStridedLoad(
   MemoryLocation ML = MemoryLocation::getAfter(PtrOperand, AAInfo);
   bool AddToChain = !AA || !AA->pointsToConstantMemory(ML);
   SDValue InChain = AddToChain ? DAG.getRoot() : DAG.getEntryNode();
+  unsigned AS = PtrOperand->getPointerAddressSpace();
   MachineMemOperand *MMO = DAG.getMachineFunction().getMachineMemOperand(
-      MachinePointerInfo(PtrOperand), MachineMemOperand::MOLoad,
+      MachinePointerInfo(AS), MachineMemOperand::MOLoad,
       MemoryLocation::UnknownSize, *Alignment, AAInfo, Ranges);
 
   SDValue LD = DAG.getStridedLoadVP(VT, DL, InChain, OpValues[0], OpValues[1],
@@ -8039,8 +8040,9 @@ void SelectionDAGBuilder::visitVPStridedStore(
   if (!Alignment)
     Alignment = DAG.getEVTAlign(VT.getScalarType());
   AAMDNodes AAInfo = VPIntrin.getAAMetadata();
+  unsigned AS = PtrOperand->getPointerAddressSpace();
   MachineMemOperand *MMO = DAG.getMachineFunction().getMachineMemOperand(
-      MachinePointerInfo(PtrOperand), MachineMemOperand::MOStore,
+      MachinePointerInfo(AS), MachineMemOperand::MOStore,
       MemoryLocation::UnknownSize, *Alignment, AAInfo);
 
   SDValue ST = DAG.getStridedStoreVP(

[arsenm]

testcase?

[topperc]

@arsenm do you want a test case for the scheduling issue? Or just a test to show we don't put a pointer in the MMO?

[arsenm]

@arsenm do you want a test case for the scheduling issue? Or just a test to show we don't put a pointer in the MMO?

Either I guess. The MMO is more targeted but the scheduling is more interesting