Add runtime support for __cpu_model (__builtin_cpu_supports)

[asbirlea]

Summary

This aims to add support for cpu_model and address Bug 25510. It uses the code from lib/Support/Host.cpp for cpu detection, and creates cpu_model with that info.

Tested on OSX, it builts successfully, but the current version does *not* resolve Bug 25510. The __cpu_model symbol is present in the library but it only gets loaded with -all_load. This patch will not land until this issue is clarified.

Built on Linux as well (though libgcc is the default). The use of "asm" required -std=gnu99, hence the cmake change. Corrections on better addressing this are welcome.

Note: See additional comments on D20988 (committed as r271921).

[echristo]

Please go ahead and clang-format the file.

Reviewing the rest now.

-eric

[asbirlea]

• clang-format it

[mehdi_amini]

lib/builtins/cpu_model.c

710

This definition (which should probably be documented as (with the previous declaration) *is* the public API of this file) is a "common" (tentative definition in C).
On MachO, these are not part of the symbol table (I had to pull my "Joker card" Nick Kledzik to figure) in the static archive by default.

I can see as solution:

• make sure we run ranlib -c on the archive to include the common in the symbol table
• make the file a C++ file (there is no "tentative definition" and as such "common" in C++).
• build with -fno-common
• Define the symbol with an explicit initialization: } __cpu_model = { 0, 0, 0, { 0 } };

(I may miss other possible solutions)

[asbirlea]

Huh, I learnt something new (*wishing this info was added to man nm*). Thanks, Mehdi!
Testing with the explicit initialization, since it seems like the simplest solution. If a different solution is preferred, please let me know.

[echristo]

Aha. Knew I was missing something... the lack of being in the symbol table was it :)

Thanks Mehdi.

I think an explicit instantiation is probably easier than the rest of them - though running ranlib -c isn't a bad idea either.

-eric

[asbirlea]

• Add default initialization. Add unit test. Note: Lit support is not set up for the compiler-rt's builtins.

[joerg]

I really, really strongly wants to go back to the drawing board with this, including the way the GCC builtin is lowered in first place. There are a number of very big concerns I have and I don't think the current implementation fits:

(1) No constructors in builtins. They introduce fundamental issues for a number of use cases of compiler-rt, like pretty much any self-hosting environment. There is no need either -- for __builtin_cpu_supports, only a few global words are needed and the content is idempotent. That means checking if a flag is set and replacing the content is perfectly fine and comes with minimal overhead.

(2) For the purpose of __builtin_cpu_supports, only the flags are needed. That means 90% of the code complexity here is unnecessary.

(3) No string interfaces, please. IMO the semantic contract for __builtin_cpu_supports should require a string constant as argument, variables should be rejected. The target lowering should then replace the string with the corresponding feature mask. The basic goal here is to avoid having to maintain string->bitmask tables in compiler-rt. I don't want to have to tell people that they need to update central libraries just because someone decided to add a new flag to the list. That approach doesn't scale and the problem of having multiple libgcc_s versions around should be a good indicator of why to avoid this kind of problems.

(4) For the latter work of identifying the CPU, I'm included to make similar requirements. I don't think it belongs into a low-level library like compiler-rt at all, but even then the low-level code should at most expose vendor + cpu family counter. I most explicitly don't want to have an enumeration of all known Intel and AMD CPUs as string table in compiler-rt.

[echristo]

In D21033#451370, @joerg wrote:

I really, really strongly wants to go back to the drawing board with this, including the way the GCC builtin is lowered in first place. There are a number of very big concerns I have and I don't think the current implementation fits:

(1) No constructors in builtins. They introduce fundamental issues for a number of use cases of compiler-rt, like pretty much any self-hosting environment. There is no need either -- for __builtin_cpu_supports, only a few global words are needed and the content is idempotent. That means checking if a flag is set and replacing the content is perfectly fine and comes with minimal overhead.

Could you explain more? Also talk about how this works with ifunc resolution and uses of builtin_cpu_is and builtin_cpu_supports in ifunc resolver functions.

(2) For the purpose of __builtin_cpu_supports, only the flags are needed. That means 90% of the code complexity here is unnecessary.

This isn't just for __builtin_cpu_supports. That's just what Alina needed here.

(3) No string interfaces, please. IMO the semantic contract for __builtin_cpu_supports should require a string constant as argument, variables should be rejected. The target lowering should then replace the string with the corresponding feature mask. The basic goal here is to avoid having to maintain string->bitmask tables in compiler-rt. I don't want to have to tell people that they need to update central libraries just because someone decided to add a new flag to the list. That approach doesn't scale and the problem of having multiple libgcc_s versions around should be a good indicator of why to avoid this kind of problems.

(4) For the latter work of identifying the CPU, I'm included to make similar requirements. I don't think it belongs into a low-level library like compiler-rt at all, but even then the low-level code should at most expose vendor + cpu family counter. I most explicitly don't want to have an enumeration of all known Intel and AMD CPUs as string table in compiler-rt.

This is talking about a new interface. While I'm somewhat sympathetic to your goals, having a compiler-rt that's a drop in replacement for libgcc unfortunately needs this feature set to be implemented. Also see arguments against implementing ifunc in the first place versus just a (possibly hidden) global that's set at program start time.

-eric

[asbirlea]

If I understand correctly, your suggestion is having correct behavior
for builtin_cpu_supports
(i.e. setting the flags) and undefined behavior (or return 0 / always
generic) for builtin_cpu_is (i.e. not setting cpu type and subtype),
because of the lack of uses for the latter, code bloat, hardship to
maintain/add new CPU generations. Is this right?

[joerg]

lib/builtins/cpu_model.c

729

This assumption will bit us, BTW. We've bug reports for OpenSSL crashing not too long ago on CPUs without CPUID support. At least for i386, presence definitely must be checked first via the corresponding eflags bit.

[echristo]

lib/builtins/cpu_model.c

729

Yeesh. You should probably update the code in Host.cpp then :)

[asbirlea]

lib/builtins/cpu_model.c

729

I'm not familiar with what flags need to be checked. Could you elaborate or update Host.cpp to resolve this?

[joerg]

lib/builtins/cpu_model.c

729

Take a look at clang's cpuid.h and __get_cpuid_max. I wonder if we can/should assume the presence of that header. What's the Windows situation here?

[asbirlea]

lib/builtins/cpu_model.c

729

Is this roughly what you had in mind?

// insert @:730; also include cpuid.h
+ MaxLeaf = __get_cpuid_max(0, &Vendor);
+ if(!MaxLeaf)
+ return -1;

Alternatively just copy the check ifdefed by i386?
Both options will work from preliminary builds.

The plan was to support Windows as well. I'm not clear if this will still be the case.

[joerg]

lib/builtins/cpu_model.c

729

Yeah, copying the ifdef is likely the best approach. Depending on the header was more a question for Host.cpp.

[asbirlea]

Check cpuid supported for i386.

[asbirlea]

Note: I can add the same check in Host.cpp in a later patch.

[asbirlea]

Pinging patch.

[asbirlea]

Weekly ping. As clang supports builtins, I believe it's worth having the same runtime support as libgcc.

[echristo]

I agree that we should add the support here. I understand Joerg's wish for a better API, but for drop in compatibility with libgcc we should still define these and perhaps conditionally compile them if we get a better library interface in the future (i.e. compatibility or not).

Thanks a lot for doing this!

-eric

ps One inline request before you commit, thanks. :)

lib/builtins/cpu_model.c

123

Please add a block comment above this that spells out that we took it from lib/Support/Host.cpp.

[asbirlea]

clang-format (minor)

[asbirlea]

Added comments identifing code source

lib/builtins/CMakeLists.txt

set(GENERIC_SOURCES
   clear_cache.c
   clzdi2.c
   clzsi2.c
   clzti2.c
   cmpdi2.c
   cmpti2.c
   comparedf2.c
   comparesf2.c
+  cpu_model.c
   ctzdi2.c
   ctzsi2.c
   ctzti2.c
   divdc3.c
   divdf3.c
   divdi3.c
   divmoddi4.c
   divmodsi4.c

 
 add_custom_target(builtins)
 
 if (APPLE)
   add_subdirectory(Darwin-excludes)
   add_subdirectory(macho_embedded)
   darwin_add_builtin_libraries(${BUILTIN_SUPPORTED_OS})
 else ()
-  append_string_if(COMPILER_RT_HAS_STD_C99_FLAG -std=c99 maybe_stdc99)
+  append_string_if(COMPILER_RT_HAS_STD_C99_FLAG -std=gnu99 maybe_stdc99)
 
   foreach (arch ${BUILTIN_SUPPORTED_ARCH})
     if (CAN_TARGET_${arch})
       # Filter out generic versions of routines that are re-implemented in
       # architecture specific manner.  This prevents multiple definitions of the
       # same symbols, making the symbol selection non-deterministic.
       foreach (_file ${${arch}_SOURCES})
         if (${_file} MATCHES ${arch}/*)

lib/builtins/cpu_model.c

+//===-- cpu_model.c - Support for __cpu_model builtin  ------------*- C -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file is based on LLVM's lib/Support/Host.cpp.
+//  It implements the operating system Host concept and builtin
+//  __cpu_model for the compiler_rt library.
+//
+//===----------------------------------------------------------------------===//
+
+#include <assert.h>
+
+#define bool int
+#define true 1
+#define false 0
+
+#ifdef _MSC_VER
+#include <intrin.h>
+#endif
+
+enum VendorSignatures {
+  SIG_INTEL = 0x756e6547 /* Genu */,
+  SIG_AMD = 0x68747541 /* Auth */
+};
+
+enum ProcessorVendors {
+  VENDOR_INTEL = 1,
+  VENDOR_AMD,
+  VENDOR_OTHER,
+  VENDOR_MAX
+};
+
+enum ProcessorTypes {
+  INTEL_ATOM = 1,
+  INTEL_CORE2,
+  INTEL_COREI7,
+  AMDFAM10H,
+  AMDFAM15H,
+  INTEL_i386,
+  INTEL_i486,
+  INTEL_PENTIUM,
+  INTEL_PENTIUM_PRO,
+  INTEL_PENTIUM_II,
+  INTEL_PENTIUM_III,
+  INTEL_PENTIUM_IV,
+  INTEL_PENTIUM_M,
+  INTEL_CORE_DUO,
+  INTEL_XEONPHI,
+  INTEL_X86_64,
+  INTEL_NOCONA,
+  INTEL_PRESCOTT,
+  AMD_i486,
+  AMDPENTIUM,
+  AMDATHLON,
+  AMDFAM14H,
+  AMDFAM16H,
+  CPU_TYPE_MAX
+};
+
+enum ProcessorSubtypes {
+  INTEL_COREI7_NEHALEM = 1,
+  INTEL_COREI7_WESTMERE,
+  INTEL_COREI7_SANDYBRIDGE,
+  AMDFAM10H_BARCELONA,
+  AMDFAM10H_SHANGHAI,
+  AMDFAM10H_ISTANBUL,
+  AMDFAM15H_BDVER1,
+  AMDFAM15H_BDVER2,
+  INTEL_PENTIUM_MMX,
+  INTEL_CORE2_65,
+  INTEL_CORE2_45,
+  INTEL_COREI7_IVYBRIDGE,
+  INTEL_COREI7_HASWELL,
+  INTEL_COREI7_BROADWELL,
+  INTEL_COREI7_SKYLAKE,
+  INTEL_COREI7_SKYLAKE_AVX512,
+  INTEL_ATOM_BONNELL,
+  INTEL_ATOM_SILVERMONT,
+  INTEL_KNIGHTS_LANDING,
+  AMDPENTIUM_K6,
+  AMDPENTIUM_K62,
+  AMDPENTIUM_K63,
+  AMDPENTIUM_GEODE,
+  AMDATHLON_TBIRD,
+  AMDATHLON_MP,
+  AMDATHLON_XP,
+  AMDATHLON_K8SSE3,
+  AMDATHLON_OPTERON,
+  AMDATHLON_FX,
+  AMDATHLON_64,
+  AMD_BTVER1,
+  AMD_BTVER2,
+  AMDFAM15H_BDVER3,
+  AMDFAM15H_BDVER4,
+  CPU_SUBTYPE_MAX
+};
+
+enum ProcessorFeatures {
+  FEATURE_CMOV = 0,
+  FEATURE_MMX,
+  FEATURE_POPCNT,
+  FEATURE_SSE,
+  FEATURE_SSE2,
+  FEATURE_SSE3,
+  FEATURE_SSSE3,
+  FEATURE_SSE4_1,
+  FEATURE_SSE4_2,
+  FEATURE_AVX,
+  FEATURE_AVX2,
+  FEATURE_AVX512,
+  FEATURE_AVX512SAVE,
+  FEATURE_MOVBE,
+  FEATURE_ADX,
+  FEATURE_EM64T
+};
+
+#if defined(i386) || defined(__i386__) || defined(__x86__) ||                  \
+    defined(_M_IX86) || defined(__x86_64__) || defined(_M_AMD64) ||            \
+    defined(_M_X64)
+
+/// 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__)
+#if defined(__x86_64__) || defined(_M_AMD64) || defined(_M_X64)
+  // gcc doesn't know cpuid would clobber ebx/rbx. Preseve it manually.
+  asm("movq\t%%rbx, %%rsi\n\t"
+      "cpuid\n\t"
+      "xchgq\t%%rbx, %%rsi\n\t"
+      : "=a"(*rEAX), "=S"(*rEBX), "=c"(*rECX), "=d"(*rEDX)
+      : "a"(value));
+  return false;
+#elif defined(i386) || defined(__i386__) || defined(__x86__) || defined(_M_IX86)
+  asm("movl\t%%ebx, %%esi\n\t"
+      "cpuid\n\t"
+      "xchgl\t%%ebx, %%esi\n\t"
+      : "=a"(*rEAX), "=S"(*rEBX), "=c"(*rECX), "=d"(*rEDX)
+      : "a"(value));
+  return false;
+// pedantic #else returns to appease -Wunreachable-code (so we don't generate
+// postprocessed code that looks like "return true; return false;")
+#else
+  return true;
+#endif
+#elif defined(_MSC_VER)
+  // The MSVC intrinsic is portable across x86 and x64.
+  int registers[4];
+  __cpuid(registers, value);
+  *rEAX = registers[0];
+  *rEBX = registers[1];
+  *rECX = registers[2];
+  *rEDX = registers[3];
+  return false;
+#else
+  return true;
+#endif
+}
+
+/// getX86CpuIDAndInfoEx - Execute the specified cpuid with subleaf and return
+/// the 4 values in the specified arguments.  If we can't run cpuid on the host,
+/// return true.
+static bool getX86CpuIDAndInfoEx(unsigned value, unsigned subleaf,
+                                 unsigned *rEAX, unsigned *rEBX, unsigned *rECX,
+                                 unsigned *rEDX) {
+#if defined(__x86_64__) || defined(_M_AMD64) || defined(_M_X64)
+#if defined(__GNUC__)
+  // gcc doesn't know cpuid would clobber ebx/rbx. Preseve it manually.
+  asm("movq\t%%rbx, %%rsi\n\t"
+      "cpuid\n\t"
+      "xchgq\t%%rbx, %%rsi\n\t"
+      : "=a"(*rEAX), "=S"(*rEBX), "=c"(*rECX), "=d"(*rEDX)
+      : "a"(value), "c"(subleaf));
+  return false;
+#elif defined(_MSC_VER)
+  int registers[4];
+  __cpuidex(registers, value, subleaf);
+  *rEAX = registers[0];
+  *rEBX = registers[1];
+  *rECX = registers[2];
+  *rEDX = registers[3];
+  return false;
+#else
+  return true;
+#endif
+#elif defined(i386) || defined(__i386__) || defined(__x86__) || defined(_M_IX86)
+#if defined(__GNUC__)
+  asm("movl\t%%ebx, %%esi\n\t"
+      "cpuid\n\t"
+      "xchgl\t%%ebx, %%esi\n\t"
+      : "=a"(*rEAX), "=S"(*rEBX), "=c"(*rECX), "=d"(*rEDX)
+      : "a"(value), "c"(subleaf));
+  return false;
+#elif defined(_MSC_VER)
+  __asm {
+      mov   eax,value
+      mov   ecx,subleaf
+      cpuid
+      mov   esi,rEAX
+      mov   dword ptr [esi],eax
+      mov   esi,rEBX
+      mov   dword ptr [esi],ebx
+      mov   esi,rECX
+      mov   dword ptr [esi],ecx
+      mov   esi,rEDX
+      mov   dword ptr [esi],edx
+  }
+  return false;
+#else
+  return true;
+#endif
+#else
+  return true;
+#endif
+}
+
+static bool getX86XCR0(unsigned *rEAX, unsigned *rEDX) {
+#if defined(__GNUC__)
+  // Check xgetbv; this uses a .byte sequence instead of the instruction
+  // directly because older assemblers do not include support for xgetbv and
+  // there is no easy way to conditionally compile based on the assembler used.
+  __asm__(".byte 0x0f, 0x01, 0xd0" : "=a"(*rEAX), "=d"(*rEDX) : "c"(0));
+  return false;
+#elif defined(_MSC_FULL_VER) && defined(_XCR_XFEATURE_ENABLED_MASK)
+  unsigned long long Result = _xgetbv(_XCR_XFEATURE_ENABLED_MASK);
+  *rEAX = Result;
+  *rEDX = Result >> 32;
+  return false;
+#else
+  return true;
+#endif
+}
+
+#endif
+
+static void detectX86FamilyModel(unsigned EAX, unsigned *Family,
+                                 unsigned *Model) {
+  *Family = (EAX >> 8) & 0xf; // Bits 8 - 11
+  *Model = (EAX >> 4) & 0xf;  // Bits 4 - 7
+  if (*Family == 6 || *Family == 0xf) {
+    if (*Family == 0xf)
+      // Examine extended family ID if family ID is F.
+      *Family += (EAX >> 20) & 0xff; // Bits 20 - 27
+    // Examine extended model ID if family ID is 6 or F.
+    *Model += ((EAX >> 16) & 0xf) << 4; // Bits 16 - 19
+  }
+}
+
+static void getIntelProcessorTypeAndSubtype(unsigned int Family,
+                                            unsigned int Model,
+                                            unsigned int Brand_id,
+                                            unsigned int Features,
+                                            unsigned *Type, unsigned *Subtype) {
+  if (Brand_id != 0)
+    return;
+  switch (Family) {
+  case 3:
+    *Type = INTEL_i386;
+    break;
+  case 4:
+    switch (Model) {
+    case 0: // Intel486 DX processors
+    case 1: // Intel486 DX processors
+    case 2: // Intel486 SX processors
+    case 3: // Intel487 processors, IntelDX2 OverDrive processors,
+            // IntelDX2 processors
+    case 4: // Intel486 SL processor
+    case 5: // IntelSX2 processors
+    case 7: // Write-Back Enhanced IntelDX2 processors
+    case 8: // IntelDX4 OverDrive processors, IntelDX4 processors
+    default:
+      *Type = INTEL_i486;
+      break;
+    }
+  case 5:
+    switch (Model) {
+    case 1: // Pentium OverDrive processor for Pentium processor (60, 66),
+            // Pentium processors (60, 66)
+    case 2: // Pentium OverDrive processor for Pentium processor (75, 90,
+            // 100, 120, 133), Pentium processors (75, 90, 100, 120, 133,
+            // 150, 166, 200)
+    case 3: // Pentium OverDrive processors for Intel486 processor-based
+            // systems
+      *Type = INTEL_PENTIUM;
+      break;
+    case 4: // Pentium OverDrive processor with MMX technology for Pentium
+            // processor (75, 90, 100, 120, 133), Pentium processor with
+            // MMX technology (166, 200)
+      *Type = INTEL_PENTIUM;
+      *Subtype = INTEL_PENTIUM_MMX;
+      break;
+    default:
+      *Type = INTEL_PENTIUM;
+      break;
+    }
+  case 6:
+    switch (Model) {
+    case 0x01: // Pentium Pro processor
+      *Type = INTEL_PENTIUM_PRO;
+      break;
+    case 0x03: // Intel Pentium II OverDrive processor, Pentium II processor,
+               // model 03
+    case 0x05: // Pentium II processor, model 05, Pentium II Xeon processor,
+               // model 05, and Intel Celeron processor, model 05
+    case 0x06: // Celeron processor, model 06
+      *Type = INTEL_PENTIUM_II;
+      break;
+    case 0x07: // Pentium III processor, model 07, and Pentium III Xeon
+               // processor, model 07
+    case 0x08: // Pentium III processor, model 08, Pentium III Xeon processor,
+               // model 08, and Celeron processor, model 08
+    case 0x0a: // Pentium III Xeon processor, model 0Ah
+    case 0x0b: // Pentium III processor, model 0Bh
+      *Type = INTEL_PENTIUM_III;
+      break;
+    case 0x09: // Intel Pentium M processor, Intel Celeron M processor model 09.
+    case 0x0d: // Intel Pentium M processor, Intel Celeron M processor, model
+               // 0Dh. All processors are manufactured using the 90 nm process.
+    case 0x15: // Intel EP80579 Integrated Processor and Intel EP80579
+               // Integrated Processor with Intel QuickAssist Technology
+      *Type = INTEL_PENTIUM_M;
+      break;
+    case 0x0e: // Intel Core Duo processor, Intel Core Solo processor, model
+               // 0Eh. All processors are manufactured using the 65 nm process.
+      *Type = INTEL_CORE_DUO;
+      break;   // yonah
+    case 0x0f: // Intel Core 2 Duo processor, Intel Core 2 Duo mobile
+               // processor, Intel Core 2 Quad processor, Intel Core 2 Quad
+               // mobile processor, Intel Core 2 Extreme processor, Intel
+               // Pentium Dual-Core processor, Intel Xeon processor, model
+               // 0Fh. All processors are manufactured using the 65 nm process.
+    case 0x16: // Intel Celeron processor model 16h. All processors are
+               // manufactured using the 65 nm process
+      *Type = INTEL_CORE2; // "core2"
+      *Subtype = INTEL_CORE2_65;
+      break;
+    case 0x17: // Intel Core 2 Extreme processor, Intel Xeon processor, model
+               // 17h. All processors are manufactured using the 45 nm process.
+               //
+               // 45nm: Penryn , Wolfdale, Yorkfield (XE)
+    case 0x1d: // Intel Xeon processor MP. All processors are manufactured using
+               // the 45 nm process.
+      *Type = INTEL_CORE2; // "penryn"
+      *Subtype = INTEL_CORE2_45;
+      break;
+    case 0x1a: // Intel Core i7 processor and Intel Xeon processor. All
+               // processors are manufactured using the 45 nm process.
+    case 0x1e: // Intel(R) Core(TM) i7 CPU         870  @ 2.93GHz.
+               // As found in a Summer 2010 model iMac.
+    case 0x1f:
+    case 0x2e:              // Nehalem EX
+      *Type = INTEL_COREI7; // "nehalem"
+      *Subtype = INTEL_COREI7_NEHALEM;
+      break;
+    case 0x25: // Intel Core i7, laptop version.
+    case 0x2c: // Intel Core i7 processor and Intel Xeon processor. All
+               // processors are manufactured using the 32 nm process.
+    case 0x2f: // Westmere EX
+      *Type = INTEL_COREI7; // "westmere"
+      *Subtype = INTEL_COREI7_WESTMERE;
+      break;
+    case 0x2a: // Intel Core i7 processor. All processors are manufactured
+               // using the 32 nm process.
+    case 0x2d:
+      *Type = INTEL_COREI7; //"sandybridge"
+      *Subtype = INTEL_COREI7_SANDYBRIDGE;
+      break;
+    case 0x3a:
+    case 0x3e:              // Ivy Bridge EP
+      *Type = INTEL_COREI7; // "ivybridge"
+      *Subtype = INTEL_COREI7_IVYBRIDGE;
+      break;
+
+    // Haswell:
+    case 0x3c:
+    case 0x3f:
+    case 0x45:
+    case 0x46:
+      *Type = INTEL_COREI7; // "haswell"
+      *Subtype = INTEL_COREI7_HASWELL;
+      break;
+
+    // Broadwell:
+    case 0x3d:
+    case 0x47:
+    case 0x4f:
+    case 0x56:
+      *Type = INTEL_COREI7; // "broadwell"
+      *Subtype = INTEL_COREI7_BROADWELL;
+      break;
+
+    // Skylake:
+    case 0x4e:
+      *Type = INTEL_COREI7; // "skylake-avx512"
+      *Subtype = INTEL_COREI7_SKYLAKE_AVX512;
+      break;
+    case 0x5e:
+      *Type = INTEL_COREI7; // "skylake"
+      *Subtype = INTEL_COREI7_SKYLAKE;
+      break;
+
+    case 0x1c: // Most 45 nm Intel Atom processors
+    case 0x26: // 45 nm Atom Lincroft
+    case 0x27: // 32 nm Atom Medfield
+    case 0x35: // 32 nm Atom Midview
+    case 0x36: // 32 nm Atom Midview
+      *Type = INTEL_ATOM;
+      *Subtype = INTEL_ATOM_BONNELL;
+      break; // "bonnell"
+
+    // Atom Silvermont codes from the Intel software optimization guide.
+    case 0x37:
+    case 0x4a:
+    case 0x4d:
+    case 0x5a:
+    case 0x5d:
+    case 0x4c: // really airmont
+      *Type = INTEL_ATOM;
+      *Subtype = INTEL_ATOM_SILVERMONT;
+      break; // "silvermont"
+
+    case 0x57:
+      *Type = INTEL_XEONPHI; // knl
+      *Subtype = INTEL_KNIGHTS_LANDING;
+      break;
+
+    default: // Unknown family 6 CPU, try to guess.
+      if (Features & (1 << FEATURE_AVX512)) {
+        *Type = INTEL_XEONPHI; // knl
+        *Subtype = INTEL_KNIGHTS_LANDING;
+        break;
+      }
+      if (Features & (1 << FEATURE_ADX)) {
+        *Type = INTEL_COREI7;
+        *Subtype = INTEL_COREI7_BROADWELL;
+        break;
+      }
+      if (Features & (1 << FEATURE_AVX2)) {
+        *Type = INTEL_COREI7;
+        *Subtype = INTEL_COREI7_HASWELL;
+        break;
+      }
+      if (Features & (1 << FEATURE_AVX)) {
+        *Type = INTEL_COREI7;
+        *Subtype = INTEL_COREI7_SANDYBRIDGE;
+        break;
+      }
+      if (Features & (1 << FEATURE_SSE4_2)) {
+        if (Features & (1 << FEATURE_MOVBE)) {
+          *Type = INTEL_ATOM;
+          *Subtype = INTEL_ATOM_SILVERMONT;
+        } else {
+          *Type = INTEL_COREI7;
+          *Subtype = INTEL_COREI7_NEHALEM;
+        }
+        break;
+      }
+      if (Features & (1 << FEATURE_SSE4_1)) {
+        *Type = INTEL_CORE2; // "penryn"
+        *Subtype = INTEL_CORE2_45;
+        break;
+      }
+      if (Features & (1 << FEATURE_SSSE3)) {
+        if (Features & (1 << FEATURE_MOVBE)) {
+          *Type = INTEL_ATOM;
+          *Subtype = INTEL_ATOM_BONNELL; // "bonnell"
+        } else {
+          *Type = INTEL_CORE2; // "core2"
+          *Subtype = INTEL_CORE2_65;
+        }
+        break;
+      }
+      if (Features & (1 << FEATURE_EM64T)) {
+        *Type = INTEL_X86_64;
+        break; // x86-64
+      }
+      if (Features & (1 << FEATURE_SSE2)) {
+        *Type = INTEL_PENTIUM_M;
+        break;
+      }
+      if (Features & (1 << FEATURE_SSE)) {
+        *Type = INTEL_PENTIUM_III;
+        break;
+      }
+      if (Features & (1 << FEATURE_MMX)) {
+        *Type = INTEL_PENTIUM_II;
+        break;
+      }
+      *Type = INTEL_PENTIUM_PRO;
+      break;
+    }
+  case 15: {
+    switch (Model) {
+    case 0: // Pentium 4 processor, Intel Xeon processor. All processors are
+            // model 00h and manufactured using the 0.18 micron process.
+    case 1: // Pentium 4 processor, Intel Xeon processor, Intel Xeon
+            // processor MP, and Intel Celeron processor. All processors are
+            // model 01h and manufactured using the 0.18 micron process.
+    case 2: // Pentium 4 processor, Mobile Intel Pentium 4 processor - M,
+            // Intel Xeon processor, Intel Xeon processor MP, Intel Celeron
+            // processor, and Mobile Intel Celeron processor. All processors
+            // are model 02h and manufactured using the 0.13 micron process.
+      *Type =
+          ((Features & (1 << FEATURE_EM64T)) ? INTEL_X86_64 : INTEL_PENTIUM_IV);
+      break;
+
+    case 3: // Pentium 4 processor, Intel Xeon processor, Intel Celeron D
+            // processor. All processors are model 03h and manufactured using
+            // the 90 nm process.
+    case 4: // Pentium 4 processor, Pentium 4 processor Extreme Edition,
+            // Pentium D processor, Intel Xeon processor, Intel Xeon
+            // processor MP, Intel Celeron D processor. All processors are
+            // model 04h and manufactured using the 90 nm process.
+    case 6: // Pentium 4 processor, Pentium D processor, Pentium processor
+            // Extreme Edition, Intel Xeon processor, Intel Xeon processor
+            // MP, Intel Celeron D processor. All processors are model 06h
+            // and manufactured using the 65 nm process.
+      *Type =
+          ((Features & (1 << FEATURE_EM64T)) ? INTEL_NOCONA : INTEL_PRESCOTT);
+      break;
+
+    default:
+      *Type =
+          ((Features & (1 << FEATURE_EM64T)) ? INTEL_X86_64 : INTEL_PENTIUM_IV);
+      break;
+    }
+  }
+  default:
+    break; /*"generic"*/
+  }
+}
+
+static void getAMDProcessorTypeAndSubtype(unsigned int Family,
+                                          unsigned int Model,
+                                          unsigned int Features, unsigned *Type,
+                                          unsigned *Subtype) {
+  // FIXME: this poorly matches the generated SubtargetFeatureKV table.  There
+  // appears to be no way to generate the wide variety of AMD-specific targets
+  // from the information returned from CPUID.
+  switch (Family) {
+  case 4:
+    *Type = AMD_i486;
+  case 5:
+    *Type = AMDPENTIUM;
+    switch (Model) {
+    case 6:
+    case 7:
+      *Subtype = AMDPENTIUM_K6;
+      break; // "k6"
+    case 8:
+      *Subtype = AMDPENTIUM_K62;
+      break; // "k6-2"
+    case 9:
+    case 13:
+      *Subtype = AMDPENTIUM_K63;
+      break; // "k6-3"
+    case 10:
+      *Subtype = AMDPENTIUM_GEODE;
+      break; // "geode"
+    default:
+      break;
+    }
+  case 6:
+    *Type = AMDATHLON;
+    switch (Model) {
+    case 4:
+      *Subtype = AMDATHLON_TBIRD;
+      break; // "athlon-tbird"
+    case 6:
+    case 7:
+    case 8:
+      *Subtype = AMDATHLON_MP;
+      break; // "athlon-mp"
+    case 10:
+      *Subtype = AMDATHLON_XP;
+      break; // "athlon-xp"
+    default:
+      break;
+    }
+  case 15:
+    *Type = AMDATHLON;
+    if (Features & (1 << FEATURE_SSE3)) {
+      *Subtype = AMDATHLON_K8SSE3;
+      break; // "k8-sse3"
+    }
+    switch (Model) {
+    case 1:
+      *Subtype = AMDATHLON_OPTERON;
+      break; // "opteron"
+    case 5:
+      *Subtype = AMDATHLON_FX;
+      break; // "athlon-fx"; also opteron
+    default:
+      *Subtype = AMDATHLON_64;
+      break; // "athlon64"
+    }
+  case 16:
+    *Type = AMDFAM10H; // "amdfam10"
+    switch (Model) {
+    case 2:
+      *Subtype = AMDFAM10H_BARCELONA;
+      break;
+    case 4:
+      *Subtype = AMDFAM10H_SHANGHAI;
+      break;
+    case 8:
+      *Subtype = AMDFAM10H_ISTANBUL;
+      break;
+    default:
+      break;
+    }
+  case 20:
+    *Type = AMDFAM14H;
+    *Subtype = AMD_BTVER1;
+    break; // "btver1";
+  case 21:
+    *Type = AMDFAM15H;
+    if (!(Features &
+          (1 << FEATURE_AVX))) { // If no AVX support, provide a sane fallback.
+      *Subtype = AMD_BTVER1;
+      break; // "btver1"
+    }
+    if (Model >= 0x50 && Model <= 0x6f) {
+      *Subtype = AMDFAM15H_BDVER4;
+      break; // "bdver4"; 50h-6Fh: Excavator
+    }
+    if (Model >= 0x30 && Model <= 0x3f) {
+      *Subtype = AMDFAM15H_BDVER3;
+      break; // "bdver3"; 30h-3Fh: Steamroller
+    }
+    if (Model >= 0x10 && Model <= 0x1f) {
+      *Subtype = AMDFAM15H_BDVER2;
+      break; // "bdver2"; 10h-1Fh: Piledriver
+    }
+    if (Model <= 0x0f) {
+      *Subtype = AMDFAM15H_BDVER1;
+      break; // "bdver1"; 00h-0Fh: Bulldozer
+    }
+    break;
+  case 22:
+    *Type = AMDFAM16H;
+    if (!(Features &
+          (1 << FEATURE_AVX))) { // If no AVX support provide a sane fallback.
+      *Subtype = AMD_BTVER1;
+      break; // "btver1";
+    }
+    *Subtype = AMD_BTVER2;
+    break; // "btver2"
+  default:
+    break; // "generic"
+  }
+}
+
+unsigned getAvailableFeatures(unsigned int ECX, unsigned int EDX,
+                              unsigned MaxLeaf) {
+  unsigned Features = 0;
+  unsigned int EAX, EBX;
+  Features |= (((EDX >> 23) & 1) << FEATURE_MMX);
+  Features |= (((EDX >> 25) & 1) << FEATURE_SSE);
+  Features |= (((EDX >> 26) & 1) << FEATURE_SSE2);
+  Features |= (((ECX >> 0) & 1) << FEATURE_SSE3);
+  Features |= (((ECX >> 9) & 1) << FEATURE_SSSE3);
+  Features |= (((ECX >> 19) & 1) << FEATURE_SSE4_1);
+  Features |= (((ECX >> 20) & 1) << FEATURE_SSE4_2);
+  Features |= (((ECX >> 22) & 1) << FEATURE_MOVBE);
+
+  // If CPUID indicates support for XSAVE, XRESTORE and AVX, and XGETBV
+  // indicates that the AVX registers will be saved and restored on context
+  // switch, then we have full AVX support.
+  const unsigned AVXBits = (1 << 27) | (1 << 28);
+  bool HasAVX = ((ECX & AVXBits) == AVXBits) && !getX86XCR0(&EAX, &EDX) &&
+                ((EAX & 0x6) == 0x6);
+  bool HasAVX512Save = HasAVX && ((EAX & 0xe0) == 0xe0);
+  bool HasLeaf7 =
+      MaxLeaf >= 0x7 && !getX86CpuIDAndInfoEx(0x7, 0x0, &EAX, &EBX, &ECX, &EDX);
+  bool HasADX = HasLeaf7 && ((EBX >> 19) & 1);
+  bool HasAVX2 = HasAVX && HasLeaf7 && (EBX & 0x20);
+  bool HasAVX512 = HasLeaf7 && HasAVX512Save && ((EBX >> 16) & 1);
+  Features |= (HasAVX << FEATURE_AVX);
+  Features |= (HasAVX2 << FEATURE_AVX2);
+  Features |= (HasAVX512 << FEATURE_AVX512);
+  Features |= (HasAVX512Save << FEATURE_AVX512SAVE);
+  Features |= (HasADX << FEATURE_ADX);
+
+  getX86CpuIDAndInfo(0x80000001, &EAX, &EBX, &ECX, &EDX);
+  Features |= (((EDX >> 29) & 0x1) << FEATURE_EM64T);
+  return Features;
+}
+
+#ifdef HAVE_INIT_PRIORITY
+#define CONSTRUCTOR_PRIORITY (101)
+#else
+#define CONSTRUCTOR_PRIORITY
+#endif
+
+int __cpu_indicator_init(void)
+    __attribute__((constructor CONSTRUCTOR_PRIORITY));
+
+struct __processor_model {
+  unsigned int __cpu_vendor;
+  unsigned int __cpu_type;
+  unsigned int __cpu_subtype;
+  unsigned int __cpu_features[1];
+} __cpu_model = { 0, 0, 0, { 0 } };
+
+/* A constructor function that is sets __cpu_model and __cpu_features with
+   the right values.  This needs to run only once.  This constructor is
+   given the highest priority and it should run before constructors without
+   the priority set.  However, it still runs after ifunc initializers and
+   needs to be called explicitly there.  */
+
+int __attribute__((constructor CONSTRUCTOR_PRIORITY))
+__cpu_indicator_init(void) {
+  unsigned int EAX, EBX, ECX, EDX;
+  unsigned int MaxLeaf = 5;
+  unsigned int Vendor;
+  unsigned int Model, Family, Brand_id;
+  unsigned int Features = 0;
+
+  /* This function needs to run just once.  */
+  if (__cpu_model.__cpu_vendor)
+    return 0;
+
+  /* Assume cpuid insn present. Run in level 0 to get vendor id. */
+  if (getX86CpuIDAndInfo(0, &MaxLeaf, &Vendor, &ECX, &EDX)) {
+    __cpu_model.__cpu_vendor = VENDOR_OTHER;
+    return -1;
+  }
+
+  if (MaxLeaf < 1 || getX86CpuIDAndInfo(1, &EAX, &EBX, &ECX, &EDX)) {
+    __cpu_model.__cpu_vendor = VENDOR_OTHER;
+    return -1;
+  }
+
+  detectX86FamilyModel(EAX, &Family, &Model);
+  Brand_id = EBX & 0xff;
+
+  /* Find available features. */
+  Features = getAvailableFeatures(ECX, EDX, MaxLeaf);
+  __cpu_model.__cpu_features[0] = Features;
+
+  if (Vendor == SIG_INTEL) {
+    /* Get CPU type.  */
+    getIntelProcessorTypeAndSubtype(Family, Model, Brand_id, Features,
+                                    &(__cpu_model.__cpu_type),
+                                    &(__cpu_model.__cpu_subtype));
+    __cpu_model.__cpu_vendor = VENDOR_INTEL;
+  } else if (Vendor == SIG_AMD) {
+    /* Get CPU type.  */
+    getAMDProcessorTypeAndSubtype(Family, Model, Features,
+                                  &(__cpu_model.__cpu_type),
+                                  &(__cpu_model.__cpu_subtype));
+    __cpu_model.__cpu_vendor = VENDOR_AMD;
+  } else
+    __cpu_model.__cpu_vendor = VENDOR_OTHER;
+
+  assert(__cpu_model.__cpu_vendor < VENDOR_MAX);
+  assert(__cpu_model.__cpu_type < CPU_TYPE_MAX);
+  assert(__cpu_model.__cpu_subtype < CPU_SUBTYPE_MAX);
+
+  return 0;
+}

test/builtins/Unit/cpu_model_test.c

+//===-- cpu_model_test.c - Test __builtin_cpu_supports -------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file tests __builtin_cpu_supports for the compiler_rt library.
+//
+//===----------------------------------------------------------------------===//
+
+int main (void) {
+  if(__builtin_cpu_supports("avx2"))
+    return 4;
+  else
+    return 3;
+}