[X86] LowerBITREVERSE - add handling for all legal 128/256/512-bit vector types, not just vXi8

Move the BITREVERSE(BSWAP(X)) expansion into LowerBITREVERSE to help simplify #81764

Author: RKSimon

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -1241,11 +1241,11 @@ X86TargetLowering::X86TargetLowering(const X86TargetMachine &TM,
     setOperationAction(ISD::ABS,                MVT::v16i8, Legal);
     setOperationAction(ISD::ABS,                MVT::v8i16, Legal);
     setOperationAction(ISD::ABS,                MVT::v4i32, Legal);
-    setOperationAction(ISD::BITREVERSE,         MVT::v16i8, Custom);
-    setOperationAction(ISD::CTLZ,               MVT::v16i8, Custom);
-    setOperationAction(ISD::CTLZ,               MVT::v8i16, Custom);
-    setOperationAction(ISD::CTLZ,               MVT::v4i32, Custom);
-    setOperationAction(ISD::CTLZ,               MVT::v2i64, Custom);
+
+    for (auto VT : {MVT::v16i8, MVT::v8i16, MVT::v4i32, MVT::v2i64}) {
+      setOperationAction(ISD::BITREVERSE,       VT, Custom);
+      setOperationAction(ISD::CTLZ,             VT, Custom);
+    }
 
     // These might be better off as horizontal vector ops.
     setOperationAction(ISD::ADD,                MVT::i16, Custom);
@@ -1341,10 +1341,6 @@ X86TargetLowering::X86TargetLowering(const X86TargetMachine &TM,
     // XOP can efficiently perform BITREVERSE with VPPERM.
     for (auto VT : { MVT::i8, MVT::i16, MVT::i32, MVT::i64 })
       setOperationAction(ISD::BITREVERSE, VT, Custom);
-
-    for (auto VT : { MVT::v16i8, MVT::v8i16,  MVT::v4i32, MVT::v2i64,
-                     MVT::v32i8, MVT::v16i16, MVT::v8i32, MVT::v4i64 })
-      setOperationAction(ISD::BITREVERSE, VT, Custom);
   }
 
   if (!Subtarget.useSoftFloat() && Subtarget.hasAVX()) {
@@ -1461,12 +1457,11 @@ X86TargetLowering::X86TargetLowering(const X86TargetMachine &TM,
     setOperationAction(ISD::TRUNCATE,          MVT::v32i32, Custom);
     setOperationAction(ISD::TRUNCATE,          MVT::v32i64, Custom);
 
-    setOperationAction(ISD::BITREVERSE,        MVT::v32i8, Custom);
-
     for (auto VT : { MVT::v32i8, MVT::v16i16, MVT::v8i32, MVT::v4i64 }) {
       setOperationAction(ISD::SETCC,           VT, Custom);
       setOperationAction(ISD::CTPOP,           VT, Custom);
       setOperationAction(ISD::CTLZ,            VT, Custom);
+      setOperationAction(ISD::BITREVERSE,      VT, Custom);
 
       // The condition codes aren't legal in SSE/AVX and under AVX512 we use
       // setcc all the way to isel and prefer SETGT in some isel patterns.
@@ -1841,8 +1836,6 @@ X86TargetLowering::X86TargetLowering(const X86TargetMachine &TM,
     setOperationAction(ISD::SMULO, MVT::v64i8, Custom);
     setOperationAction(ISD::UMULO, MVT::v64i8, Custom);
 
-    setOperationAction(ISD::BITREVERSE, MVT::v64i8,  Custom);
-
     for (auto VT : { MVT::v64i8, MVT::v32i16, MVT::v16i32, MVT::v8i64 }) {
       setOperationAction(ISD::SRL,              VT, Custom);
       setOperationAction(ISD::SHL,              VT, Custom);
@@ -1852,6 +1845,7 @@ X86TargetLowering::X86TargetLowering(const X86TargetMachine &TM,
       setOperationAction(ISD::SETCC,            VT, Custom);
       setOperationAction(ISD::ABDS,             VT, Custom);
       setOperationAction(ISD::ABDU,             VT, Custom);
+      setOperationAction(ISD::BITREVERSE,       VT, Custom);
 
       // The condition codes aren't legal in SSE/AVX and under AVX512 we use
       // setcc all the way to isel and prefer SETGT in some isel patterns.
@@ -31180,17 +31174,25 @@ static SDValue LowerBITREVERSE(SDValue Op, const X86Subtarget &Subtarget,
   SDValue In = Op.getOperand(0);
   SDLoc DL(Op);
 
-  assert(VT.getScalarType() == MVT::i8 &&
-         "Only byte vector BITREVERSE supported");
-
-  // Split v64i8 without BWI so that we can still use the PSHUFB lowering.
-  if (VT == MVT::v64i8 && !Subtarget.hasBWI())
+  // Split 512-bit ops without BWI so that we can still use the PSHUFB lowering.
+  if (VT.is512BitVector() && !Subtarget.hasBWI())
     return splitVectorIntUnary(Op, DAG);
 
   // Decompose 256-bit ops into smaller 128-bit ops on pre-AVX2.
-  if (VT == MVT::v32i8 && !Subtarget.hasInt256())
+  if (VT.is256BitVector() && !Subtarget.hasInt256())
     return splitVectorIntUnary(Op, DAG);
 
+  // Lower vXi16/vXi32/vXi64 as BSWAP + vXi8 BITREVERSE.
+  if (VT.getScalarType() != MVT::i8) {
+    MVT ByteVT = MVT::getVectorVT(MVT::i8, VT.getSizeInBits() / 8);
+    SDValue Res = DAG.getNode(ISD::BSWAP, DL, VT, In);
+    Res = DAG.getBitcast(ByteVT, Res);
+    Res = DAG.getNode(ISD::BITREVERSE, DL, ByteVT, Res);
+    return DAG.getBitcast(VT, Res);
+  }
+  assert(VT.isVector() && VT.getScalarType() == MVT::i8 &&
+         "Only byte vector BITREVERSE supported");
+
   unsigned NumElts = VT.getVectorNumElements();
 
   // If we have GFNI, we can use GF2P8AFFINEQB to reverse the bits.