[X86] Simplify the BRCOND handling for FCMP_UNE.

[craig.topper]

Summary

Despite what the comment says, FCMP_UNE would be an OR not an AND. In the lowering code the first branch created still goes to the original destination. The second branch was exchanged to go to where the subsequent unconditional branch went. This is different than what we do for FCMP_OEQ where both branches that we create go to the original unconditional branch.

As far as I can tell, I think this means we don't need to exchange the branch target with the unconditional branch for FCMP_UNE at all.

[craig.topper]

Ping

[spatel]

LGTM

llvm/trunk/lib/Target/X86/X86ISelLowering.cpp

if (Cond.hasOneUse() && isAndOrOfSetCCs(Cond, CondOpc)) {
           CC = DAG.getConstant(X86::COND_P, dl, MVT::i8);
           Cond = Cmp;
           addTest = false;
         }
       }
     } else if (Cond.getOpcode() == ISD::SETCC &&
                cast<CondCodeSDNode>(Cond.getOperand(2))->get() == ISD::SETUNE) {
       // For FCMP_UNE, we can emit
-      // two branches instead of an explicit AND instruction with a
-      // separate test. However, we only do this if this block doesn't
-      // have a fall-through edge, because this requires an explicit
-      // jmp when the condition is false.
-      if (Op.getNode()->hasOneUse()) {
-        SDNode *User = *Op.getNode()->use_begin();
-        // Look for an unconditional branch following this conditional branch.
-        // We need this because we need to reverse the successors in order
-        // to implement FCMP_UNE.
-        if (User->getOpcode() == ISD::BR) {
-          SDValue FalseBB = User->getOperand(1);
-          SDNode *NewBR =
-            DAG.UpdateNodeOperands(User, User->getOperand(0), Dest);
-          assert(NewBR == User);
-          (void)NewBR;
-
-          SDValue Cmp = DAG.getNode(X86ISD::CMP, dl, MVT::i32,
-                                    Cond.getOperand(0), Cond.getOperand(1));
-          Cmp = ConvertCmpIfNecessary(Cmp, DAG);
-          CC = DAG.getConstant(X86::COND_NE, dl, MVT::i8);
-          Chain = DAG.getNode(X86ISD::BRCOND, dl, Op.getValueType(),
-                              Chain, Dest, CC, Cmp);
-          CC = DAG.getConstant(X86::COND_NP, dl, MVT::i8);
-          Cond = Cmp;
-          addTest = false;
-          Dest = FalseBB;
-        }
-      }
+      // two branches instead of an explicit OR instruction with a
+      // separate test.
+      CC = DAG.getConstant(X86::COND_P, dl, MVT::i8);
     }
   }
 
   if (addTest) {
     // Look pass the truncate if the high bits are known zero.
     if (isTruncWithZeroHighBitsInput(Cond, DAG))
         Cond = Cond.getOperand(0);