[X86] Emit comments explaining the immediate in vfpclass

This makes the assembly a lot more readable at a glance.

As an example:
```
  vfpclasspd $4, %zmm0, %k0 # k0 = isNegativeZero(zmm0)
```

1 files changed, 81 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/MCTargetDesc/X86InstComments.cpp b/llvm/lib/Target/X86/MCTargetDesc/X86InstComments.cpp
index 587f923..49e8bab 100644
--- a/llvm/lib/Target/X86/MCTargetDesc/X86InstComments.cpp
+++ b/llvm/lib/Target/X86/MCTargetDesc/X86InstComments.cpp
@@ -40,6 +40,20 @@ using namespace llvm;
   CASE_MASK_INS_COMMON(Inst, Suffix, src)         \
   CASE_MASKZ_INS_COMMON(Inst, Suffix, src)
 
+#define CASE_FPCLASS_PACKED(Inst, src)    \
+  CASE_AVX_INS_COMMON(Inst, Z, r##src)    \
+  CASE_AVX_INS_COMMON(Inst, Z256, r##src) \
+  CASE_AVX_INS_COMMON(Inst, Z128, r##src) \
+  CASE_MASK_INS_COMMON(Inst, Z, r##src)
+
+#define CASE_FPCLASS_PACKED_MEM(Inst) \
+  CASE_FPCLASS_PACKED(Inst, m)        \
+  CASE_FPCLASS_PACKED(Inst, mb)
+
+#define CASE_FPCLASS_SCALAR(Inst, src)  \
+  CASE_AVX_INS_COMMON(Inst, Z, r##src)  \
+  CASE_MASK_INS_COMMON(Inst, Z, r##src)
+
 #define CASE_PTERNLOG(Inst, src)                                               \
   CASE_AVX512_INS_COMMON(Inst, Z, r##src##i)                                   \
   CASE_AVX512_INS_COMMON(Inst, Z256, r##src##i)                                \
@@ -949,6 +963,70 @@ static bool printPTERNLOGComments(const MCInst *MI, raw_ostream &OS,
   return true;
 }
 
+static bool printFPCLASSComments(const MCInst *MI, raw_ostream &OS,
+                                 const MCInstrInfo &MCII) {
+  unsigned NumOperands = MI->getNumOperands();
+  int SrcIdx;
+  switch (MI->getOpcode()) {
+    CASE_FPCLASS_PACKED(FPCLASSPBF16, r)
+    CASE_FPCLASS_PACKED(FPCLASSPH, r)
+    CASE_FPCLASS_PACKED(FPCLASSPS, r)
+    CASE_FPCLASS_PACKED(FPCLASSPD, r)
+    CASE_FPCLASS_SCALAR(FPCLASSSH, r)
+    CASE_FPCLASS_SCALAR(FPCLASSSS, r)
+    CASE_FPCLASS_SCALAR(FPCLASSSD, r) {
+      SrcIdx = NumOperands - 2;
+      break;
+    }
+    CASE_FPCLASS_PACKED_MEM(FPCLASSPBF16)
+    CASE_FPCLASS_PACKED_MEM(FPCLASSPH)
+    CASE_FPCLASS_PACKED_MEM(FPCLASSPS)
+    CASE_FPCLASS_PACKED_MEM(FPCLASSPD)
+    CASE_FPCLASS_SCALAR(FPCLASSSH, m)
+    CASE_FPCLASS_SCALAR(FPCLASSSS, m)
+    CASE_FPCLASS_SCALAR(FPCLASSSD, m) {
+      SrcIdx = -1;
+      break;
+    }
+  default:
+    return false;
+  }
+  StringRef DestName = getRegName(MI->getOperand(0).getReg());
+  StringRef SrcName =
+      SrcIdx != -1 ? getRegName(MI->getOperand(SrcIdx).getReg()) : "mem";
+
+  OS << DestName;
+  printMasking(OS, MI, MCII);
+  OS << " = ";
+
+  uint8_t Categories = MI->getOperand(NumOperands - 1).getImm();
+  if (Categories == 0) {
+    OS << "false";
+  } else {
+    static constexpr StringLiteral CategoryNames[] = {
+      "QuietNaN",
+      "PositiveZero",
+      "NegativeZero",
+      "PositiveInfinity",
+      "NegativeInfinity",
+      "Subnormal",
+      "Negative",
+      "SignalingNaN",
+    };
+    bool Conjoin = false;
+    for (size_t I = 0, E = std::size(CategoryNames); I != E; ++I) {
+      if (Categories & (1 << I)) {
+        if (Conjoin)
+          OS << " | ";
+        Conjoin = true;
+        OS << "is" << CategoryNames[I] << '(' << SrcName << ')';
+      }
+    }
+  }
+  OS << '\n';
+  return true;
+}
+
 //===----------------------------------------------------------------------===//
 // Top Level Entrypoint
 //===----------------------------------------------------------------------===//
@@ -970,6 +1048,9 @@ bool llvm::EmitAnyX86InstComments(const MCInst *MI, raw_ostream &OS,
   if (printPTERNLOGComments(MI, OS, MCII))
     return true;
 
+  if (printFPCLASSComments(MI, OS, MCII))
+    return true;
+
   switch (MI->getOpcode()) {
   default:
     // Not an instruction for which we can decode comments.