[llvm-commits] [llvm] r45245 - /llvm/trunk/lib/CodeGen/MachineLICM.cpp

[Bill Wendling]

Author: void
Date: Wed Dec 19 19:08:10 2007
New Revision: 45245

URL: http://llvm.org/viewvc/llvm-project?rev=45245&view=rev
Log:
Updated comments to reflect what "side effects" means in this situation.

Modified:
    llvm/trunk/lib/CodeGen/MachineLICM.cpp

Modified: llvm/trunk/lib/CodeGen/MachineLICM.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/MachineLICM.cpp?rev=45245&r1=45244&r2=45245&view=diff

==============================================================================
--- llvm/trunk/lib/CodeGen/MachineLICM.cpp (original)
+++ llvm/trunk/lib/CodeGen/MachineLICM.cpp Wed Dec 19 19:08:10 2007
@@ -249,8 +249,8 @@
 
 /// IsLoopInvariantInst - Returns true if the instruction is loop
 /// invariant. I.e., all virtual register operands are defined outside of the
-/// loop, physical registers aren't accessed (explicitly or implicitly), and the
-/// instruction is hoistable.
+/// loop, physical registers aren't accessed explicitly, and there are no side
+/// effects that aren't captured by the operands or other flags.
 /// 
 bool MachineLICM::IsLoopInvariantInst(MachineInstr &I) {
   DEBUG({
@@ -281,13 +281,6 @@
         DOUT << "  * Instruction has side effects.\n";
     });
 
-#if 0
-  // FIXME: Don't hoist if this instruction implicitly reads physical registers.
-  if (I.getInstrDescriptor()->ImplicitUses ||
-      I.getInstrDescriptor()->ImplicitDefs)
-    return false;
-#endif
-
   // The instruction is loop invariant if all of its operands are loop-invariant
   for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i) {
     const MachineOperand &MO = I.getOperand(i);
@@ -309,7 +302,7 @@
       return false;
   }
 
-  // Don't hoist something that has side effects.
+  // Don't hoist something that has unmodelled side effects.
   if (TII->hasUnmodelledSideEffects(&I)) return false;
 
   // If we got this far, the instruction is loop invariant!