[llvm-commits] [llvm] r97352 - /llvm/trunk/lib/CodeGen/MachineLICM.cpp

[Dan Gohman]

Author: djg
Date: Sat Feb 27 18:08:44 2010
New Revision: 97352

URL: http://llvm.org/viewvc/llvm-project?rev=97352&view=rev
Log:
Don't unconditionally suppress hoisting of instructions with implicit
defs or uses. The regular def and use checking below covers them, and
can be more precise. It's safe to hoist an instruction with a dead
implicit def if the register isn't live into the loop header.

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=97352&r1=97351&r2=97352&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/MachineLICM.cpp (original)
+++ llvm/trunk/lib/CodeGen/MachineLICM.cpp Sat Feb 27 18:08:44 2010
@@ -252,32 +252,6 @@
       return false;
   }
 
-  DEBUG({
-      dbgs() << "--- Checking if we can hoist " << I;
-      if (I.getDesc().getImplicitUses()) {
-        dbgs() << "  * Instruction has implicit uses:\n";
-
-        const TargetRegisterInfo *TRI = TM->getRegisterInfo();
-        for (const unsigned *ImpUses = I.getDesc().getImplicitUses();
-             *ImpUses; ++ImpUses)
-          dbgs() << "      -> " << TRI->getName(*ImpUses) << "\n";
-      }
-
-      if (I.getDesc().getImplicitDefs()) {
-        dbgs() << "  * Instruction has implicit defines:\n";
-
-        const TargetRegisterInfo *TRI = TM->getRegisterInfo();
-        for (const unsigned *ImpDefs = I.getDesc().getImplicitDefs();
-             *ImpDefs; ++ImpDefs)
-          dbgs() << "      -> " << TRI->getName(*ImpDefs) << "\n";
-      }
-    });
-
-  if (I.getDesc().getImplicitDefs() || I.getDesc().getImplicitUses()) {
-    DEBUG(dbgs() << "Cannot hoist with implicit defines or uses\n");
-    return false;
-  }
-
   // The instruction is loop invariant if all of its operands are.
   for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i) {
     const MachineOperand &MO = I.getOperand(i);
@@ -311,6 +285,10 @@
       } else if (!MO.isDead()) {
         // A def that isn't dead. We can't move it.
         return false;
+      } else if (CurLoop->getHeader()->isLiveIn(Reg)) {
+        // If the reg is live into the loop, we can't hoist an instruction
+        // which would clobber it.
+        return false;
       }
     }