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.

llvm-svn: 97352

1 files changed, 4 insertions, 26 deletions

diff --git a/llvm/lib/CodeGen/MachineLICM.cpp b/llvm/lib/CodeGen/MachineLICM.cpp
index 92c84f3e836..5580ec13f4f 100644
--- a/llvm/lib/CodeGen/MachineLICM.cpp
+++ b/llvm/lib/CodeGen/MachineLICM.cpp
@@ -252,32 +252,6 @@ bool MachineLICM::IsLoopInvariantInst(MachineInstr &I) {
       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 @@ bool MachineLICM::IsLoopInvariantInst(MachineInstr &I) {
       } 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;
       }
     }