[x86] clean up materializeSBB(); NFCI

This is producing SBB where it is obviously not necessary, so it needs to be limited.

llvm-svn: 296894

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -33863,22 +33863,19 @@ static SDValue combineGatherScatter(SDNode *N, SelectionDAG &DAG) {
   return SDValue();
 }
 
-// Helper function of performSETCCCombine. It is to materialize "setb reg"
-// as "sbb reg,reg", since it can be extended without zext and produces
-// an all-ones bit which is more useful than 0/1 in some cases.
-static SDValue MaterializeSETB(const SDLoc &DL, SDValue EFLAGS,
-                               SelectionDAG &DAG, MVT VT) {
+/// Materialize "setb reg" as "sbb reg,reg", since it produces an all-ones bit
+/// which is more useful than 0/1 in some cases.
+static SDValue materializeSBB(SDNode *N, SDValue EFLAGS, SelectionDAG &DAG) {
+  SDLoc DL(N);
+  // "Condition code B" is also known as "the carry flag" (CF).
+  SDValue CF = DAG.getConstant(X86::COND_B, DL, MVT::i8);
+  SDValue SBB = DAG.getNode(X86ISD::SETCC_CARRY, DL, MVT::i8, CF, EFLAGS);
+  MVT VT = N->getSimpleValueType(0);
   if (VT == MVT::i8)
-    return DAG.getNode(ISD::AND, DL, VT,
-                       DAG.getNode(X86ISD::SETCC_CARRY, DL, MVT::i8,
-                                   DAG.getConstant(X86::COND_B, DL, MVT::i8),
-                                   EFLAGS),
-                       DAG.getConstant(1, DL, VT));
-  assert (VT == MVT::i1 && "Unexpected type for SECCC node");
-  return DAG.getNode(ISD::TRUNCATE, DL, MVT::i1,
-                     DAG.getNode(X86ISD::SETCC_CARRY, DL, MVT::i8,
-                                 DAG.getConstant(X86::COND_B, DL, MVT::i8),
-                                 EFLAGS));
+    return DAG.getNode(ISD::AND, DL, VT, SBB, DAG.getConstant(1, DL, VT));
+
+  assert(VT == MVT::i1 && "Unexpected type for SETCC node");
+  return DAG.getNode(ISD::TRUNCATE, DL, MVT::i1, SBB);
 }
 
 // Optimize  RES = X86ISD::SETCC CONDCODE, EFLAG_INPUT
@@ -33902,15 +33899,12 @@ static SDValue combineX86SetCC(SDNode *N, SelectionDAG &DAG,
                                    EFLAGS.getNode()->getVTList(),
                                    EFLAGS.getOperand(1), EFLAGS.getOperand(0));
       SDValue NewEFLAGS = SDValue(NewSub.getNode(), EFLAGS.getResNo());
-      return MaterializeSETB(DL, NewEFLAGS, DAG, N->getSimpleValueType(0));
+      return materializeSBB(N, NewEFLAGS, DAG);
     }
   }
 
-  // Materialize "setb reg" as "sbb reg,reg", since it can be extended without
-  // a zext and produces an all-ones bit which is more useful than 0/1 in some
-  // cases.
   if (CC == X86::COND_B)
-    return MaterializeSETB(DL, EFLAGS, DAG, N->getSimpleValueType(0));
+    return materializeSBB(N, EFLAGS, DAG);
 
   // Try to simplify the EFLAGS and condition code operands.
   if (SDValue Flags = combineSetCCEFLAGS(EFLAGS, CC, DAG))