[X86][SSE] Rename truncateVectorCompareWithPACKSS to truncateVectorWithPACKSS. NFC.

We no longer rely on the vector source being a comparison result, just have sufficient sign bits.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@316834 91177308-0d34-0410-b5e6-96231b3b80d8

Author: RKSimon

lib/Target/X86/X86ISelLowering.cpp

@@ -15990,14 +15990,13 @@ static SDValue LowerZERO_EXTEND(SDValue Op, const X86Subtarget &Subtarget,
 }
 
 /// Helper to recursively truncate vector elements in half with PACKSS.
-/// It makes use of the fact that vector comparison results will be all-zeros
-/// or all-ones to prevent the PACKSS from saturating the results.
+/// It makes use of the fact that vectors with enough leading sign bits
+/// prevent the PACKSS from saturating the results.
 /// AVX2 (Int256) sub-targets require extra shuffling as the PACKSS operates
 /// within each 128-bit lane.
-static SDValue truncateVectorCompareWithPACKSS(EVT DstVT, SDValue In,
-                                               const SDLoc &DL,
-                                               SelectionDAG &DAG,
-                                               const X86Subtarget &Subtarget) {
+static SDValue truncateVectorWithPACKSS(EVT DstVT, SDValue In, const SDLoc &DL,
+                                        SelectionDAG &DAG,
+                                        const X86Subtarget &Subtarget) {
   // Requires SSE2 but AVX512 has fast truncate.
   if (!Subtarget.hasSSE2() || Subtarget.hasAVX512())
     return SDValue();
@@ -16065,18 +16064,18 @@ static SDValue truncateVectorCompareWithPACKSS(EVT DstVT, SDValue In,
     // If 512bit -> 128bit truncate another stage.
     EVT PackedVT = EVT::getVectorVT(Ctx, PackedSVT, NumElems);
     Res = DAG.getBitcast(PackedVT, Res);
-    return truncateVectorCompareWithPACKSS(DstVT, Res, DL, DAG, Subtarget);
+    return truncateVectorWithPACKSS(DstVT, Res, DL, DAG, Subtarget);
   }
 
   // Recursively pack lower/upper subvectors, concat result and pack again.
   assert(SrcSizeInBits >= 512 && "Expected 512-bit vector or greater");
   EVT PackedVT = EVT::getVectorVT(Ctx, PackedSVT, NumSubElts);
-  Lo = truncateVectorCompareWithPACKSS(PackedVT, Lo, DL, DAG, Subtarget);
-  Hi = truncateVectorCompareWithPACKSS(PackedVT, Hi, DL, DAG, Subtarget);
+  Lo = truncateVectorWithPACKSS(PackedVT, Lo, DL, DAG, Subtarget);
+  Hi = truncateVectorWithPACKSS(PackedVT, Hi, DL, DAG, Subtarget);
 
   PackedVT = EVT::getVectorVT(Ctx, PackedSVT, NumElems);
   SDValue Res = DAG.getNode(ISD::CONCAT_VECTORS, DL, PackedVT, Lo, Hi);
-  return truncateVectorCompareWithPACKSS(DstVT, Res, DL, DAG, Subtarget);
+  return truncateVectorWithPACKSS(DstVT, Res, DL, DAG, Subtarget);
 }
 
 static SDValue LowerTruncateVecI1(SDValue Op, SelectionDAG &DAG,
@@ -16140,7 +16139,7 @@ SDValue X86TargetLowering::LowerTRUNCATE(SDValue Op, SelectionDAG &DAG) const {
 
   // Truncate with PACKSS if we are truncating a vector zero/all-bits result.
   if (InVT.getScalarSizeInBits() == DAG.ComputeNumSignBits(In))
-    if (SDValue V = truncateVectorCompareWithPACKSS(VT, In, DL, DAG, Subtarget))
+    if (SDValue V = truncateVectorWithPACKSS(VT, In, DL, DAG, Subtarget))
       return V;
 
   if ((VT == MVT::v4i32) && (InVT == MVT::v4i64)) {
@@ -34328,7 +34327,7 @@ static SDValue combineVectorSignBitsTruncation(SDNode *N, SDLoc &DL,
   if (InSVT != MVT::i16 && InSVT != MVT::i32 && InSVT != MVT::i64)
     return SDValue();
 
-  return truncateVectorCompareWithPACKSS(VT, In, DL, DAG, Subtarget);
+  return truncateVectorWithPACKSS(VT, In, DL, DAG, Subtarget);
 }
 
 static SDValue combineTruncate(SDNode *N, SelectionDAG &DAG,