[compiler-rt][X86] Use functions in cpuid.h instead of inline assembly (#97877)

This patch makes the host/feature detection in compiler-rt and LLVM use
the functions provided in cpuid.h(__get_cpuid, __get_cpuid_count)
instead of inline assembly. This simplifies the implementation and moves
any inline assembly away to a more common place.

A while ago, some similar cleanup was attempted, but this ended up
resulting in some compilation errors due to toolchain minimum version
issues (https://bugs.llvm.org/show_bug.cgi?id=30384). After the
reversion landed, there have been no attempts since then to clean up the
code, even though the minimum supported compilers now support the
relevant functions (https://godbolt.org/z/o1Mjz8ndv).

Author: boomanaiden154

compiler-rt/lib/builtins/cpu_model/x86.c

@@ -23,6 +23,10 @@
 
 #include <assert.h>
 
+#if defined(__GNUC__) || defined(__clang__)
+#include <cpuid.h>
+#endif
+
 #ifdef _MSC_VER
 #include <intrin.h>
 #endif
@@ -224,38 +228,6 @@ enum ProcessorFeatures {
   CPU_FEATURE_MAX
 };
 
-// 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.
-static bool isCpuIdSupported(void) {
-#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;
-}
-
 // This code is copied from lib/Support/Host.cpp.
 // Changes to either file should be mirrored in the other.
 
@@ -264,25 +236,7 @@ static bool isCpuIdSupported(void) {
 static bool getX86CpuIDAndInfo(unsigned value, unsigned *rEAX, unsigned *rEBX,
                                unsigned *rECX, unsigned *rEDX) {
 #if defined(__GNUC__) || defined(__clang__)
-#if defined(__x86_64__)
-  // gcc doesn't know cpuid would clobber ebx/rbx. Preserve it manually.
-  // FIXME: should we save this for Clang?
-  __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__)
-  __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;
-#else
-  return true;
-#endif
+  return !__get_cpuid(value, rEAX, rEBX, rECX, rEDX);
 #elif defined(_MSC_VER)
   // The MSVC intrinsic is portable across x86 and x64.
   int registers[4];
@@ -303,26 +257,12 @@ static bool getX86CpuIDAndInfo(unsigned value, unsigned *rEAX, unsigned *rEBX,
 static bool getX86CpuIDAndInfoEx(unsigned value, unsigned subleaf,
                                  unsigned *rEAX, unsigned *rEBX, unsigned *rECX,
                                  unsigned *rEDX) {
+  // TODO(boomanaiden154): When the minimum toolchain versions for gcc and clang
+  // are such that __cpuidex is defined within cpuid.h for both, we can remove
+  // the __get_cpuid_count function and share the MSVC implementation between
+  // all three.
 #if defined(__GNUC__) || defined(__clang__)
-#if defined(__x86_64__)
-  // gcc doesn't know cpuid would clobber ebx/rbx. Preserve it manually.
-  // FIXME: should we save this for Clang?
-  __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(__i386__)
-  __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;
-#else
-  return true;
-#endif
+  return !__get_cpuid_count(value, subleaf, rEAX, rEBX, rECX, rEDX);
 #elif defined(_MSC_VER)
   int registers[4];
   __cpuidex(registers, value, subleaf);
@@ -338,6 +278,9 @@ static bool getX86CpuIDAndInfoEx(unsigned value, unsigned subleaf,
 
 // Read control register 0 (XCR0). Used to detect features such as AVX.
 static bool getX86XCR0(unsigned *rEAX, unsigned *rEDX) {
+  // TODO(boomanaiden154): When the minimum toolchain versions for gcc and clang
+  // are such that _xgetbv is supported by both, we can unify the implementation
+  // with MSVC and remove all inline assembly.
 #if defined(__GNUC__) || defined(__clang__)
   // Check xgetbv; this uses a .byte sequence instead of the instruction
   // directly because older assemblers do not include support for xgetbv and
@@ -1108,8 +1051,7 @@ int CONSTRUCTOR_ATTRIBUTE __cpu_indicator_init(void) {
   if (__cpu_model.__cpu_vendor)
     return 0;
 
-  if (!isCpuIdSupported() ||
-      getX86CpuIDAndInfo(0, &MaxLeaf, &Vendor, &ECX, &EDX) || MaxLeaf < 1) {
+  if (getX86CpuIDAndInfo(0, &MaxLeaf, &Vendor, &ECX, &EDX) || MaxLeaf < 1) {
     __cpu_model.__cpu_vendor = VENDOR_OTHER;
     return -1;
   }

llvm/lib/TargetParser/Host.cpp

@@ -50,6 +50,9 @@
 #if defined(__sun__) && defined(__svr4__)
 #include <kstat.h>
 #endif
+#if defined(__GNUC__) || defined(__clang__)
+#include <cpuid.h>
+#endif
 
 #define DEBUG_TYPE "host-detection"
 
@@ -521,68 +524,15 @@ StringRef sys::detail::getHostCPUNameForBPF() {
 #endif
 }
 
-#if defined(__i386__) || defined(_M_IX86) || \
-    defined(__x86_64__) || defined(_M_X64)
-
-// 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;
-}
+#if defined(__i386__) || defined(_M_IX86) || defined(__x86_64__) ||            \
+    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__)
-  // gcc doesn't know cpuid would clobber ebx/rbx. Preserve it manually.
-  // FIXME: should we save this for Clang?
-  __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__)
-  __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;
-#else
-  return true;
-#endif
+  return !__get_cpuid(value, rEAX, rEBX, rECX, rEDX);
 #elif defined(_MSC_VER)
   // The MSVC intrinsic is portable across x86 and x64.
   int registers[4];
@@ -609,9 +559,6 @@ VendorSignatures getVendorSignature(unsigned *MaxLeaf) {
   else
     *MaxLeaf = 0;
 
-  if (!isCpuIdSupported())
-    return VendorSignatures::UNKNOWN;
-
   if (getX86CpuIDAndInfo(0, MaxLeaf, &EBX, &ECX, &EDX) || *MaxLeaf < 1)
     return VendorSignatures::UNKNOWN;
 
@@ -639,26 +586,12 @@ using namespace llvm::sys::detail::x86;
 static bool getX86CpuIDAndInfoEx(unsigned value, unsigned subleaf,
                                  unsigned *rEAX, unsigned *rEBX, unsigned *rECX,
                                  unsigned *rEDX) {
+  // TODO(boomanaiden154): When the minimum toolchain versions for gcc and clang
+  // are such that __cpuidex is defined within cpuid.h for both, we can remove
+  // the __get_cpuid_count function and share the MSVC implementation between
+  // all three.
 #if defined(__GNUC__) || defined(__clang__)
-#if defined(__x86_64__)
-  // gcc doesn't know cpuid would clobber ebx/rbx. Preserve it manually.
-  // FIXME: should we save this for Clang?
-  __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(__i386__)
-  __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;
-#else
-  return true;
-#endif
+  return !__get_cpuid_count(value, subleaf, rEAX, rEBX, rECX, rEDX);
 #elif defined(_MSC_VER)
   int registers[4];
   __cpuidex(registers, value, subleaf);
@@ -674,6 +607,9 @@ static bool getX86CpuIDAndInfoEx(unsigned value, unsigned subleaf,
 
 // Read control register 0 (XCR0). Used to detect features such as AVX.
 static bool getX86XCR0(unsigned *rEAX, unsigned *rEDX) {
+  // TODO(boomanaiden154): When the minimum toolchain versions for gcc and clang
+  // are such that _xgetbv is supported by both, we can unify the implementation
+  // with MSVC and remove all inline assembly.
 #if defined(__GNUC__) || defined(__clang__)
   // Check xgetbv; this uses a .byte sequence instead of the instruction
   // directly because older assemblers do not include support for xgetbv and