[X86] Ensure that bit reversals of byte vectors are properly lowered on pure GFNI targets (#148304)

Fixes #148238.

When GFNI is present, custom bit reversal lowerings for scalar integers
become active. They work by swapping the bytes in the scalar value and
then reversing bits in a vector of bytes. However, the custom bit
reversal lowering for a vector of bytes is disabled if GFNI is present
in isolation, resulting messed up code.

---------

Co-authored-by: Simon Pilgrim <[email protected]>

Author: TDecking

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -1323,11 +1323,15 @@ X86TargetLowering::X86TargetLowering(const X86TargetMachine &TM,
     setOperationAction(ISD::STRICT_FDIV,        MVT::v2f64, Legal);
   }
 
-  if (Subtarget.hasGFNI()) {
+  if (!Subtarget.useSoftFloat() && Subtarget.hasGFNI()) {
     setOperationAction(ISD::BITREVERSE, MVT::i8, Custom);
     setOperationAction(ISD::BITREVERSE, MVT::i16, Custom);
     setOperationAction(ISD::BITREVERSE, MVT::i32, Custom);
     setOperationAction(ISD::BITREVERSE, MVT::i64, Custom);
+
+    for (auto VT : {MVT::v16i8, MVT::v8i16, MVT::v4i32, MVT::v2i64}) {
+      setOperationAction(ISD::BITREVERSE, VT, Custom);
+    }
   }
 
   if (!Subtarget.useSoftFloat() && Subtarget.hasSSSE3()) {
@@ -32694,7 +32698,8 @@ static SDValue LowerBITREVERSE(SDValue Op, const X86Subtarget &Subtarget,
   if (Subtarget.hasXOP() && !VT.is512BitVector())
     return LowerBITREVERSE_XOP(Op, DAG);
 
-  assert(Subtarget.hasSSSE3() && "SSSE3 required for BITREVERSE");
+  assert((Subtarget.hasSSSE3() || Subtarget.hasGFNI()) &&
+         "SSSE3 or GFNI required for BITREVERSE");
 
   SDValue In = Op.getOperand(0);
   SDLoc DL(Op);