Swap operands now preserves the semantics of the binary operator by changing

the opcode of the instruction if possible.

llvm-svn: 1444

2 files changed, 34 insertions, 4 deletions

diff --git a/llvm/include/llvm/InstrTypes.h b/llvm/include/llvm/InstrTypes.h
index 54aab328758..3d834e97a08 100644
--- a/llvm/include/llvm/InstrTypes.h
+++ b/llvm/include/llvm/InstrTypes.h
@@ -127,10 +127,14 @@ public:
 
   virtual const char *getOpcodeName() const = 0;
 
-  // swapOperands - Exchange the two operands to this instruction
-  void swapOperands() {
-    swap(Operands[0], Operands[1]);
-  }
+  // swapOperands - Exchange the two operands to this instruction.
+  // This instruction is safe to use on any binary instruction and
+  // does not modify the semantics of the instruction.  If the
+  // instruction is order dependant (SetLT f.e.) the opcode is
+  // changed.  If the instruction cannot be reversed (ie, it's a Div),
+  // then return true.
+  //
+  bool swapOperands();
 
   // Methods for support type inquiry through isa, cast, and dyn_cast:
   static inline bool classof(const BinaryOperator *) { return true; }
diff --git a/llvm/lib/VMCore/iOperators.cpp b/llvm/lib/VMCore/iOperators.cpp
index 22b6052d469..cb53d5e0344 100644
--- a/llvm/lib/VMCore/iOperators.cpp
+++ b/llvm/lib/VMCore/iOperators.cpp
@@ -53,6 +53,32 @@ BinaryOperator *BinaryOperator::create(BinaryOps Op, Value *S1, Value *S2,
   }
 }
 
+// swapOperands - Exchange the two operands to this instruction.  This
+// instruction is safe to use on any binary instruction and does not
+// modify the semantics of the instruction.  If the instruction is
+// order dependant (SetLT f.e.) the opcode is changed.
+//
+bool BinaryOperator::swapOperands() {
+  switch (getOpcode()) {
+    // Instructions that don't need opcode modification
+  case Add: case Mul:
+  case And: case Xor:
+  case Or:
+  case SetEQ: case SetNE:
+    break;
+    // Instructions that need opcode modification
+  case SetGT: iType = SetLT; break;
+  case SetLT: iType = SetGT; break;
+  case SetGE: iType = SetLE; break;
+  case SetLE: iType = SetGE; break;
+    // Error on the side of caution
+  default:
+    return true;
+  }
+  swap(Operands[0], Operands[1]);
+  return false;
+}
+
 
 //===----------------------------------------------------------------------===//
 //                            GenericBinaryInst Class