[llvm] [X86] TableGen-erate SDNode descriptions (PR #168421)

[Simon Pilgrim via llvm-commits]

================
@@ -58,70 +67,128 @@ def X86any_fmax : PatFrags<(ops node:$src1, node:$src2),
                            [(X86strict_fmax node:$src1, node:$src2),
                             (X86fmax node:$src1, node:$src2)]>;
 
+// Bitwise logical AND of floating point values. This corresponds
+// to X86::ANDPS or X86::ANDPD.
 def X86fand    : SDNode<"X86ISD::FAND",      SDTFPBinOp,
                         [SDNPCommutative, SDNPAssociative]>;
+
+// Bitwise logical OR of floating point values. This corresponds
+// to X86::ORPS or X86::ORPD.
 def X86for     : SDNode<"X86ISD::FOR",       SDTFPBinOp,
                         [SDNPCommutative, SDNPAssociative]>;
+
+// Bitwise logical XOR of floating point values. This corresponds
+// to X86::XORPS or X86::XORPD.
 def X86fxor    : SDNode<"X86ISD::FXOR",      SDTFPBinOp,
                         [SDNPCommutative, SDNPAssociative]>;
+
+//  Bitwise logical ANDNOT of floating point values. This
+// corresponds to X86::ANDNPS or X86::ANDNPD.
 def X86fandn   : SDNode<"X86ISD::FANDN",     SDTFPBinOp>;
+
+// Floating point reciprocal-sqrt and reciprocal approximation.
+// Note that these typically require refinement
+// in order to obtain suitable precision.
 def X86frsqrt  : SDNode<"X86ISD::FRSQRT",    SDTFPUnaryOp>;
 def X86frcp    : SDNode<"X86ISD::FRCP",      SDTFPUnaryOp>;
+
+// Floating point horizontal add/sub.
 def X86fhadd   : SDNode<"X86ISD::FHADD",     SDTFPBinOp>;
 def X86fhsub   : SDNode<"X86ISD::FHSUB",     SDTFPBinOp>;
+
+// Integer horizontal add/sub.
 def X86hadd    : SDNode<"X86ISD::HADD",      SDTIntBinOp>;
 def X86hsub    : SDNode<"X86ISD::HSUB",      SDTIntBinOp>;
+
+// X86 compare and logical compare instructions.
 def X86comi    : SDNode<"X86ISD::COMI",      SDTX86FCmp>;
 def X86ucomi   : SDNode<"X86ISD::UCOMI",     SDTX86FCmp>;
+
+// X86 compare with Intrinsics similar to COMI.
 def X86comi512       : SDNode<"X86ISD::COMX",      SDTX86FCmp>;
 def X86ucomi512      : SDNode<"X86ISD::UCOMX",     SDTX86FCmp>;
+
 def SDTX86Cmps : SDTypeProfile<1, 3, [SDTCisFP<0>, SDTCisSameAs<0, 1>,
                                       SDTCisSameAs<1, 2>, SDTCisVT<3, i8>]>;
+
+// X86 FP SETCC, implemented with CMP{cc}SS/CMP{cc}SD.
+// Operands are two FP values to compare; result is a mask of
+// 0s or 1s.  Generally DTRT for C/C++ with NaNs.
 def X86cmps    : SDNode<"X86ISD::FSETCC",    SDTX86Cmps>;
 
+// Shuffle 16 8-bit values within a vector.
 def X86pshufb  : SDNode<"X86ISD::PSHUFB",
                  SDTypeProfile<1, 2, [SDTCVecEltisVT<0, i8>, SDTCisSameAs<0,1>,
                                       SDTCisSameAs<0,2>]>>;
+
+// Compute Sum of Absolute Differences.
 def X86psadbw  : SDNode<"X86ISD::PSADBW",
                  SDTypeProfile<1, 2, [SDTCVecEltisVT<0, i64>,
                                       SDTCVecEltisVT<1, i8>,
                                       SDTCisSameSizeAs<0,1>,
                                       SDTCisSameAs<1,2>]>, [SDNPCommutative]>;
+
 def SDTX86PSADBW : SDTypeProfile<1, 3, [SDTCVecEltisVT<0, i16>,
                                         SDTCVecEltisVT<1, i8>,
                                         SDTCisSameSizeAs<0,1>,
                                         SDTCisSameAs<1,2>, SDTCisVT<3, i8>]>;
+
+// Compute Double Block Packed Sum-Absolute-Differences
 def X86dbpsadbw : SDNode<"X86ISD::DBPSADBW", SDTX86PSADBW>;
+
+// Bitwise Logical AND NOT of Packed FP values.
 def X86andnp   : SDNode<"X86ISD::ANDNP",
                  SDTypeProfile<1, 2, [SDTCisVec<0>, SDTCisSameAs<0,1>,
                                       SDTCisSameAs<0,2>]>>;
+
 def X86multishift   : SDNode<"X86ISD::MULTISHIFT",
                  SDTypeProfile<1, 2, [SDTCisVec<0>, SDTCisVec<1>,
                                       SDTCisSameAs<1,2>]>>;
 def X86pextrb  : SDNode<"X86ISD::PEXTRB",
----------------
RKSimon wrote:

```
// Extract a 8-bit value from a vector and zero extend it to
// i32, corresponds to X86::PEXTRB.
```

https://github.com/llvm/llvm-project/pull/168421