[cpu-detection] Copy simplified version of get_cpuid_max to remove dependency to clang's implementation

[asbirlea]

Summary

Attempting to fix PR30384.
Take the same approach as in compiler_rt and add a simplified version of __get_cpuid_max.
Including cpuid.h is no longer needed.

[echristo]

lib/Support/Host.cpp

172 ↗

(On Diff #71471)

Once we have this here can we get rid of the bits in clang?

[asbirlea]

lib/Support/Host.cpp

172 ↗

(On Diff #71471)

There is no usage of this in llvm, clang, openmp or test-suite. However there are external tools using clang that do use the original method.
I don't think that "__get_cpuid_max" can be removed.

[asbirlea]

Pinging patch.

[echristo]

OK, one inline comment.

Thanks!

-eric

lib/Support/Host.cpp

172 ↗

(On Diff #71471)

OK. Can you add a comment to that effect with what you found used externally?

[asbirlea]

Add comment.

llvm/trunk/lib/Support/Host.cpp

if (CloseStatus)
     return -1;
   return Ret;
 }
 #endif
 
 #if defined(__i386__) || defined(_M_IX86) || \
     defined(__x86_64__) || defined(_M_X64)
 
-#if defined(__GNUC__) || defined(__clang__)
-#include <cpuid.h>
-#endif
-
 enum VendorSignatures {
   SIG_INTEL = 0x756e6547 /* Genu */,
   SIG_AMD = 0x68747541 /* Auth */
 };
 
 enum ProcessorVendors {
   VENDOR_INTEL = 1,
   VENDOR_AMD,
enum ProcessorFeatures {
   FEATURE_AVX2,
   FEATURE_AVX512,
   FEATURE_AVX512SAVE,
   FEATURE_MOVBE,
   FEATURE_ADX,
   FEATURE_EM64T
 };
 
+// The check below for i386 was copied from clang's cpuid.h (__get_cpuid_max).
+// Check motivated by bug reports for OpenSSL crashing on CPUs without CPUID
+// support. Consequently, for i386, the presence of CPUID is checked first
+// via the corresponding eflags bit.
+// Removal of cpuid.h header motivated by PR30384
+// Header cpuid.h and method __get_cpuid_max are not used in llvm, clang, openmp
+// or test-suite, but are used in external projects e.g. libstdcxx
+static bool isCpuIdSupported() {
+#if defined(__GNUC__) || defined(__clang__)
+#if defined(__i386__)
+  int __cpuid_supported;
+  __asm__("  pushfl\n"
+          "  popl   %%eax\n"
+          "  movl   %%eax,%%ecx\n"
+          "  xorl   $0x00200000,%%eax\n"
+          "  pushl  %%eax\n"
+          "  popfl\n"
+          "  pushfl\n"
+          "  popl   %%eax\n"
+          "  movl   $0,%0\n"
+          "  cmpl   %%eax,%%ecx\n"
+          "  je     1f\n"
+          "  movl   $1,%0\n"
+          "1:"
+          : "=r"(__cpuid_supported)
+          :
+          : "eax", "ecx");
+  if (!__cpuid_supported)
+    return false;
+#endif
+  return true;
+#endif
+  return true;
+}
+
 /// getX86CpuIDAndInfo - Execute the specified cpuid and return the 4 values in
 /// the specified arguments.  If we can't run cpuid on the host, return true.
 static bool getX86CpuIDAndInfo(unsigned value, unsigned *rEAX, unsigned *rEBX,
                                unsigned *rECX, unsigned *rEDX) {
 #if defined(__GNUC__) || defined(__clang__) || defined(_MSC_VER)
 #if defined(__GNUC__) || defined(__clang__)
 #if defined(__x86_64__)
   // gcc doesn't know cpuid would clobber ebx/rbx. Preserve it manually.

 StringRef sys::getHostCPUName() {
   unsigned EAX = 0, EBX = 0, ECX = 0, EDX = 0;
   unsigned MaxLeaf, Vendor;
 
 #if defined(__GNUC__) || defined(__clang__)
   //FIXME: include cpuid.h from clang or copy __get_cpuid_max here
   // and simplify it to not invoke __cpuid (like cpu_model.c in
   // compiler-rt/lib/builtins/cpu_model.c?
-  if(!__get_cpuid_max(0, &Vendor))
+  // Opting for the second option.
+  if(!isCpuIdSupported())
     return "generic";
 #endif
   if (getX86CpuIDAndInfo(0, &MaxLeaf, &Vendor, &ECX, &EDX))
     return "generic";
   if (getX86CpuIDAndInfo(0x1, &EAX, &EBX, &ECX, &EDX))
     return "generic";
 
   unsigned Brand_id = EBX & 0xff;