[llvm-exegesis] Fix ifdefs in X86/Target.cpp

[kpdev42]

Summary

As discussed in https://reviews.llvm.org/D96498, the correct macro
to check together with _MSC_VER is _M_X64. Testing for _MSC_VER with
x86_64 made tests fail on Windows in https://reviews.llvm.org/D146301.

Additionally, this commit replaces a few calls to llvm_unreachable() with
report_fatal_error() because it is actually reached even on Linux/i686,
causing obscure segfaults when expanded to __builtin_unreachable().

~~

Huawei RRI, OS Lab

[kpdev42]

ping

llvm/test/tools/llvm-exegesis/X86/latency/dummy-counters.test

 # RUN: llvm-exegesis -mtriple=x86_64-unknown-unknown -mcpu=x86-64 -mode=latency -opcode-name=LEA64r --use-dummy-perf-counters | FileCheck %s
-# TODO Support non-Linux systems
-# REQUIRES: exegesis-can-execute-x86_64, system-linux
+# REQUIRES: exegesis-can-execute-x86_64
 
 CHECK:      ---
 CHECK-NEXT: mode: latency
 CHECK-NEXT: key:
 CHECK-NEXT:   instructions:
 CHECK-NEXT:     LEA64r
 # 'measurements' field should not contain misleading values
 CHECK:      measurements:    []
 CHECK:      assembled_snippet: {{[A-Z0-9]+}}{{$}}

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

 #include "X86.h"
 #include "X86Counter.h"
 #include "X86RegisterInfo.h"
 #include "llvm/ADT/Sequence.h"
 #include "llvm/CodeGen/MachineInstrBuilder.h"
 #include "llvm/MC/MCInstBuilder.h"
 #include "llvm/Support/Errc.h"
 #include "llvm/Support/Error.h"
+#include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/FormatVariadic.h"
 #include "llvm/TargetParser/Host.h"
 
 #include <memory>
 #include <string>
 #include <vector>
 #if defined(_MSC_VER) && (defined(_M_IX86) || defined(_M_X64))
 #include <immintrin.h>
 #include <intrin.h>
 #endif
-#if defined(__x86_64__) && defined(_MSC_VER)
+#if defined(_MSC_VER) && defined(_M_X64)
 #include <float.h> // For _clearfp in ~X86SavedState().
 #endif
 
 namespace llvm {
 namespace exegesis {
 
 // If a positive value is specified, we are going to use the LBR in
 // latency-mode.

 
 #include "X86GenExegesis.inc"
 
 namespace {
 
 class X86SavedState : public ExegesisTarget::SavedState {
 public:
   X86SavedState() {
-#ifdef __x86_64__
-# if defined(_MSC_VER)
+#if defined(_MSC_VER) && defined(_M_X64)
     _fxsave64(FPState);
     Eflags = __readeflags();
-# elif defined(__GNUC__)
+#elif defined(__GNUC__) && defined(__x86_64__)
     __builtin_ia32_fxsave64(FPState);
     Eflags = __builtin_ia32_readeflags_u64();
-# endif
 #else
-    llvm_unreachable("X86 exegesis running on non-X86 target");
+    report_fatal_error("X86 exegesis running on unsupported target");
 #endif
   }
 
   ~X86SavedState() {
     // Restoring the X87 state does not flush pending exceptions, make sure
     // these exceptions are flushed now.
-#ifdef __x86_64__
-# if defined(_MSC_VER)
+#if defined(_MSC_VER) && defined(_M_X64)
     _clearfp();
     _fxrstor64(FPState);
     __writeeflags(Eflags);
-# elif defined(__GNUC__)
+#elif defined(__GNUC__) && defined(__x86_64__)
     asm volatile("fwait");
     __builtin_ia32_fxrstor64(FPState);
     __builtin_ia32_writeeflags_u64(Eflags);
-# endif
 #else
-    llvm_unreachable("X86 exegesis running on non-X86 target");
+    report_fatal_error("X86 exegesis running on unsupported target");
 #endif
   }
 
 private:
-#ifdef __x86_64__
+#if defined(__x86_64__) || defined(_M_X64)
   alignas(16) char FPState[512];
   uint64_t Eflags;
 #endif
 };
 
 class ExegesisX86Target : public ExegesisTarget {
 public:
   ExegesisX86Target() : ExegesisTarget(X86CpuPfmCounters) {}

 #if defined(__i386__) || defined(_M_IX86) || defined(__x86_64__) ||            \
     defined(_M_X64)
     using namespace sys::detail::x86;
 
     if (getVendorSignature() == VendorSignatures::GENUINE_INTEL)
       // If the kernel supports it, the hardware still may not have it.
       return X86LbrCounter::checkLbrSupport();
 #else
-    llvm_unreachable("Running X86 exegesis on non-X86 target");
+    report_fatal_error("Running X86 exegesis on unsupported target");
 #endif
 #endif
     return llvm::make_error<llvm::StringError>(
         "LBR not supported on this kernel and/or platform",
         llvm::errc::not_supported);
   }
 
   std::unique_ptr<SavedState> withSavedState() const override {