[SelectionDAG] Avoid aliasing analysis if the object size is unknown.

If the size of memory access is unknown, do not use it to analysis. One
example of unknown size memory access is to load/store scalable vector
objects on the stack.

Differential Revision: https://reviews.llvm.org/D91833

1 files changed, 21 insertions, 10 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGAddressAnalysis.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGAddressAnalysis.cpp
index 3a53ab9..20c7d77 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGAddressAnalysis.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGAddressAnalysis.cpp
@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/CodeGen/SelectionDAGAddressAnalysis.h"
+#include "llvm/Analysis/MemoryLocation.h"
 #include "llvm/CodeGen/ISDOpcodes.h"
 #include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/CodeGen/MachineFunction.h"
@@ -96,18 +97,28 @@ bool BaseIndexOffset::computeAliasing(const SDNode *Op0,
   int64_t PtrDiff;
   if (NumBytes0.hasValue() && NumBytes1.hasValue() &&
       BasePtr0.equalBaseIndex(BasePtr1, DAG, PtrDiff)) {
+    // If the size of memory access is unknown, do not use it to analysis.
+    // One example of unknown size memory access is to load/store scalable
+    // vector objects on the stack.
     // BasePtr1 is PtrDiff away from BasePtr0. They alias if none of the
     // following situations arise:
-    IsAlias = !(
-        // [----BasePtr0----]
-        //                         [---BasePtr1--]
-        // ========PtrDiff========>
-        (*NumBytes0 <= PtrDiff) ||
-        //                     [----BasePtr0----]
-        // [---BasePtr1--]
-        // =====(-PtrDiff)====>
-        (PtrDiff + *NumBytes1 <= 0)); // i.e. *NumBytes1 < -PtrDiff.
-    return true;
+    if (PtrDiff >= 0 &&
+        *NumBytes0 != static_cast<int64_t>(MemoryLocation::UnknownSize)) {
+      // [----BasePtr0----]
+      //                         [---BasePtr1--]
+      // ========PtrDiff========>
+      IsAlias = !(*NumBytes0 <= PtrDiff);
+      return true;
+    }
+    if (PtrDiff < 0 &&
+        *NumBytes1 != static_cast<int64_t>(MemoryLocation::UnknownSize)) {
+      //                     [----BasePtr0----]
+      // [---BasePtr1--]
+      // =====(-PtrDiff)====>
+      IsAlias = !((PtrDiff + *NumBytes1) <= 0);
+      return true;
+    }
+    return false;
   }
   // If both BasePtr0 and BasePtr1 are FrameIndexes, we will not be
   // able to calculate their relative offset if at least one arises