[llvm-exegesis] Mark second-form X87 instructions as unsupported.

[courbet]

Summary

We only support the first form because we rely on information that is
only available there.

llvm/trunk/tools/llvm-exegesis/lib/X86/Target.cpp

 
 namespace {
 
 static llvm::Error IsInvalidOpcode(const Instruction &Instr) {
   const auto OpcodeName = Instr.Name;
   if (OpcodeName.startswith("POPF") || OpcodeName.startswith("PUSHF") ||
       OpcodeName.startswith("ADJCALLSTACK"))
     return llvm::make_error<BenchmarkFailure>(
-        "Unsupported opcode: Push/Pop/AdjCallStack");
+        "unsupported opcode: Push/Pop/AdjCallStack");
+  // We do not handle second-form X87 instructions. We only handle first-form
+  // ones (_Fp), see comment in X86InstrFPStack.td.
+  for (const Operand &Op : Instr.Operands)
+    if (Op.isReg() && Op.isExplicit() &&
+        Op.getExplicitOperandInfo().RegClass == llvm::X86::RSTRegClassID)
+      return llvm::make_error<BenchmarkFailure>(
+          "unsupported second-form X87 instruction");
   return llvm::Error::success();
 }
 
 static unsigned GetX86FPFlags(const Instruction &Instr) {
   return Instr.Description->TSFlags & llvm::X86II::FPTypeMask;
 }
 
 class X86LatencySnippetGenerator : public LatencySnippetGenerator {