[MachineLICM] Fix handling of memoperands

[oota-llvm.git] / include / llvm / CodeGen / MachineInstr.h

diff --git a/include/llvm/CodeGen/MachineInstr.h b/include/llvm/CodeGen/MachineInstr.h
index 07b1133b2a4ad4bca90607d601c3c7f5ddb32e6a..93dc0483099ca6a25a45c76e8d08d44bc3b469c6 100644 (file)
--- a/include/llvm/CodeGen/MachineInstr.h
+++ b/include/llvm/CodeGen/MachineInstr.h
@@ -92,6 +92,12 @@ private:
                                         // information to AsmPrinter.
 
   uint8_t NumMemRefs;                   // Information on memory references.
+  // Note that MemRefs == nullptr,  means 'don't know', not 'no memory access'.
+  // Calling code must treat missing information conservatively.  If the number
+  // of memory operands required to be precise exceeds the maximum value of
+  // NumMemRefs - currently 256 - we remove the operands entirely. Note also
+  // that this is a non-owning reference to a shared copy on write buffer owned
+  // by the MachineFunction and created via MF.allocateMemRefsArray. 
   mmo_iterator MemRefs;
 
   DebugLoc debugLoc;                    // Source line information.
@@ -346,6 +352,9 @@ public:
   /// Access to memory operands of the instruction
   mmo_iterator memoperands_begin() const { return MemRefs; }
   mmo_iterator memoperands_end() const { return MemRefs + NumMemRefs; }
+  /// Return true if we don't have any memory operands which described the the
+  /// memory access done by this instruction.  If this is true, calling code
+  /// must be conservative.    
   bool memoperands_empty() const { return NumMemRefs == 0; }
 
   iterator_range<mmo_iterator>  memoperands() {