[llvm][support] Fix unused variable bug caused by D97504

[oontvoo]

Summary

Detail: In D97504, I replaced the first getX86CpuIDAndInfo() call in getHhostCpuName() with getVendorSignature() (because the purpose of that was to get the vendor signature), but I hadn't noticed that it was also using the EAX (MaxLeaf) value.

[oontvoo]

updated comment

[oontvoo]

The original patch caused a failure and was reverted. So I'll move this fix to the roll-forward patch

llvm/include/llvm/Support/Host.h

#if defined(__i386__) || defined(_M_IX86) || defined(__x86_64__) ||            \
   namespace x86 {
   enum class VendorSignatures {
     UNKNOWN,
     GENUINE_INTEL,
     AUTHENTIC_AMD,
   };
 
   /// Returns the host CPU's vendor.
-  VendorSignatures getVendorSignature();
+  /// MaxLeaf: if a non-nullptr pointer is specified, the EAX value will be
+  /// assigned to its pointee.
+  VendorSignatures getVendorSignature(unsigned *MaxLeaf = nullptr);
   } // namespace x86
 #endif
   }
 }
 }
 
 #endif

llvm/lib/Support/Host.cpp

 #endif
 }
 
 namespace llvm {
 namespace sys {
 namespace detail {
 namespace x86 {
 
-VendorSignatures getVendorSignature() {
+VendorSignatures getVendorSignature(unsigned *MaxLeaf) {
   unsigned EAX = 0, EBX = 0, ECX = 0, EDX = 0;
+  if (MaxLeaf == nullptr)
+    MaxLeaf = &EAX;
 
   if (!isCpuIdSupported())
     return VendorSignatures::UNKNOWN;
 
-  if (getX86CpuIDAndInfo(0, &EAX, &EBX, &ECX, &EDX) || EAX < 1)
+  if (getX86CpuIDAndInfo(0, MaxLeaf, &EBX, &ECX, &EDX) || *MaxLeaf < 1)
     return VendorSignatures::UNKNOWN;
 
   // "Genu ineI ntel"
   if (EBX == 0x756e6547 && ECX == 0x6c65746e && EDX == 0x49656e69)
     return VendorSignatures::GENUINE_INTEL;
 
   // "Auth enti cAMD"
   if (EBX == 0x68747541 && ECX == 0x69746e65 && EDX == 0x444d4163)
#endif
   if (HasExtLeaf1 && ((ECX >> 16) & 1))
     setFeature(X86::FEATURE_FMA4);
 
   if (HasExtLeaf1 && ((EDX >> 29) & 1))
     setFeature(X86::FEATURE_64BIT);
 }
 
 StringRef sys::getHostCPUName() {
-  const VendorSignatures Vendor = getVendorSignature();
+  unsigned MaxLeaf = 0;
+  const VendorSignatures Vendor = getVendorSignature(&MaxLeaf);
   if (Vendor == VendorSignatures::UNKNOWN)
     return "generic";
 
   unsigned EAX = 0, EBX = 0, ECX = 0, EDX = 0;
   getX86CpuIDAndInfo(0x1, &EAX, &EBX, &ECX, &EDX);
 
   unsigned Family = 0, Model = 0;
   unsigned Features[(X86::CPU_FEATURE_MAX + 31) / 32] = {0};
-  unsigned MaxLeaf = 0;
   detectX86FamilyModel(EAX, &Family, &Model);
   getAvailableFeatures(ECX, EDX, MaxLeaf, Features);
 
   // These aren't consumed in this file, but we try to keep some source code the
   // same or similar to compiler-rt.
   unsigned Type = 0;
   unsigned Subtype = 0;