[llvm-commits] [llvm] r124659 - in /llvm/trunk: include/llvm/Instructions.h lib/VMCore/Instructions.cpp

[Jay Foad]

Author: foad
Date: Tue Feb  1 03:22:34 2011
New Revision: 124659

URL: http://llvm.org/viewvc/llvm-project?rev=124659&view=rev
Log:
Make SwitchInst::removeCase() more efficient.

Modified:
    llvm/trunk/include/llvm/Instructions.h
    llvm/trunk/lib/VMCore/Instructions.cpp

Modified: llvm/trunk/include/llvm/Instructions.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Instructions.h?rev=124659&r1=124658&r2=124659&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Instructions.h (original)
+++ llvm/trunk/include/llvm/Instructions.h Tue Feb  1 03:22:34 2011
@@ -2247,7 +2247,8 @@
 
   /// removeCase - This method removes the specified successor from the switch
   /// instruction.  Note that this cannot be used to remove the default
-  /// destination (successor #0).
+  /// destination (successor #0). Also note that this operation may reorder the
+  /// remaining cases at index idx and above.
   ///
   void removeCase(unsigned idx);
 

Modified: llvm/trunk/lib/VMCore/Instructions.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/VMCore/Instructions.cpp?rev=124659&r1=124658&r2=124659&view=diff
==============================================================================
--- llvm/trunk/lib/VMCore/Instructions.cpp (original)
+++ llvm/trunk/lib/VMCore/Instructions.cpp Tue Feb  1 03:22:34 2011
@@ -3009,14 +3009,10 @@
   unsigned NumOps = getNumOperands();
   Use *OL = OperandList;
 
-  // Move everything after this operand down.
-  //
-  // FIXME: we could just swap with the end of the list, then erase.  However,
-  // client might not expect this to happen.  The code as it is thrashes the
-  // use/def lists, which is kinda lame.
-  for (unsigned i = (idx+1)*2; i != NumOps; i += 2) {
-    OL[i-2] = OL[i];
-    OL[i-2+1] = OL[i+1];
+  // Overwrite this case with the end of the list.
+  if ((idx + 1) * 2 != NumOps) {
+    OL[idx * 2] = OL[NumOps - 2];
+    OL[idx * 2 + 1] = OL[NumOps - 1];
   }
 
   // Nuke the last value.