1 files changed, 21 insertions, 2 deletions
diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index 89138dd..7b456ed 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -2681,8 +2681,27 @@ llvm::Value *CodeGenFunction::FormX86ResolverCondition(
     const MultiVersionResolverOption &RO) {
   llvm::Value *Condition = nullptr;
 
-  if (!RO.Conditions.Architecture.empty())
-    Condition = EmitX86CpuIs(RO.Conditions.Architecture);
+  if (!RO.Conditions.Architecture.empty()) {
+    StringRef Arch = RO.Conditions.Architecture;
+    std::array<uint32_t, 4> Mask{};
+    // If arch= specifies an x86-64 micro-architecture level, test a special
+    // feature named FEATURE_X86_64_*, otherwise we use __builtin_cpu_is.
+    if (Arch.consume_front("x86-64")) {
+      if (Arch.empty()) // FEATURE_X86_64_BASELINE 95=2*32+31
+        Mask[2] = 1u << 31;
+      else if (Arch == "-v2") // FEATURE_X86_64_V2 96==3*32+0
+        Mask[3] = 1u << 0;
+      else if (Arch == "-v3") // FEATURE_X86_64_V3 97==3*32+1
+        Mask[3] = 1u << 1;
+      else if (Arch == "-v4") // FEATURE_X86_64_V3 98==3*32+2
+        Mask[3] = 1u << 2;
+      else
+        llvm_unreachable("invalid x86-64 micro-architecture level");
+      Condition = EmitX86CpuSupports(Mask);
+    } else {
+      Condition = EmitX86CpuIs(Arch);
+    }
+  }
 
   if (!RO.Conditions.Features.empty()) {
     llvm::Value *FeatureCond = EmitX86CpuSupports(RO.Conditions.Features);