Add a flag to indicate that an instruction is as cheap (or cheaper) than a move

instruction to execute. This can be used for transformations (like two-address
conversion) to remat an instruction instead of generating a "move"
instruction. The idea is to decrease the live ranges and register pressure and
all that jazz.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@51660 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 11 insertions, 1 deletions

diff --git a/include/llvm/Target/TargetInstrDesc.h b/include/llvm/Target/TargetInstrDesc.h
index dbfd55a..c83f8e2 100644
--- a/include/llvm/Target/TargetInstrDesc.h
+++ b/include/llvm/Target/TargetInstrDesc.h
@@ -95,7 +95,8 @@ namespace TID {
     Commutable,
     ConvertibleTo3Addr,
     UsesCustomDAGSchedInserter,
-    Rematerializable
+    Rematerializable,
+    CheapAsAMove
   };
 }
 
@@ -387,6 +388,15 @@ public:
   bool isRematerializable() const {
     return Flags & (1 << TID::Rematerializable);
   }
+
+  /// isAsCheapAsAMove - Returns true if this instruction has the same cost (or
+  /// less) than a move instruction. This is useful during certain types of
+  /// rematerializations (e.g., during two-address conversion) where we would
+  /// like to remat the instruction, but not if it costs more than moving the
+  /// instruction into the appropriate register.
+  bool isAsCheapAsAMove() const {
+    return Flags & (1 << TID::CheapAsAMove);
+  }
 };
 
 } // end namespace llvm