Add CPU family for Apple’s M1 SoC

According to reports, XNU’s CPU family identifier previously used for
the Westmere family (which Homebrew mislabels as the Arrandale family)
is now being reused for one of Apple’s M1 SoC models.

Resolve the conflict by splitting the list of CPU families and adding a
microarchitecture check.

Sources for the values:

- https://github.com/Homebrew/brew/issues/7857#issuecomment-728739049
- https://en.wikipedia.org/wiki/Comparison_of_ARMv8-A_cores
- Direct messages

Library/Homebrew/extend/os/mac/hardware/cpu.rb

@@ -22,33 +22,10 @@ module Hardware
       end
 
       def family
-        case sysctl_int("hw.cpufamily")
+        if arm?
-        when 0x73d67300 # Yonah: Core Solo/Duo
+          arm_family
-          :core
+        elsif intel?
-        when 0x426f69ef # Merom: Core 2 Duo
+          intel_family
-          :core2
-        when 0x78ea4fbc # Penryn
-          :penryn
-        when 0x6b5a4cd2 # Nehalem
-          :nehalem
-        when 0x573B5EEC # Arrandale
-          :arrandale
-        when 0x5490B78C # Sandy Bridge
-          :sandybridge
-        when 0x1F65E835 # Ivy Bridge
-          :ivybridge
-        when 0x10B282DC # Haswell
-          :haswell
-        when 0x582ed09c # Broadwell
-          :broadwell
-        when 0x37fc219f # Skylake
-          :skylake
-        when 0x0f817246 # Kaby Lake
-          :kabylake
-        when 0x38435547 # Ice Lake
-          :icelake
-        when 0x07d34b9f # ARMv8.3-A (Vortex, Tempest)
-          :arm_vortex_tempest
         else
           :dunno
         end
@@ -124,6 +101,48 @@ module Hardware
 
       private
 
+      def arm_family
+        case sysctl_int("hw.cpufamily")
+        when 0x07d34b9f             # ARMv8.3-A (Vortex, Tempest)
+          :arm_vortex_tempest
+        when 0x573b5eec, 0x1b588bb3 # ARMv8.4-A (Firestorm, Icestorm)
+          :arm_firestorm_icestorm
+        else
+          :dunno
+        end
+      end
+
+      def intel_family
+        case sysctl_int("hw.cpufamily")
+        when 0x73d67300 # Yonah: Core Solo/Duo
+          :core
+        when 0x426f69ef # Merom: Core 2 Duo
+          :core2
+        when 0x78ea4fbc # Penryn
+          :penryn
+        when 0x6b5a4cd2 # Nehalem
+          :nehalem
+        when 0x573b5eec # Arrandale
+          :arrandale
+        when 0x5490b78c # Sandy Bridge
+          :sandybridge
+        when 0x1f65e835 # Ivy Bridge
+          :ivybridge
+        when 0x10b282dc # Haswell
+          :haswell
+        when 0x582ed09c # Broadwell
+          :broadwell
+        when 0x37fc219f # Skylake
+          :skylake
+        when 0x0f817246 # Kaby Lake
+          :kabylake
+        when 0x38435547 # Ice Lake
+          :icelake
+        else
+          :dunno
+        end
+      end
+
       def sysctl_bool(key)
         sysctl_int(key) == 1
       end

Library/Homebrew/test/hardware/cpu_spec.rb

@@ -22,6 +22,7 @@ describe Hardware::CPU do
   describe "::family" do
     let(:cpu_families) {
       [
+        :arm_firestorm_icestorm,
         :arm_vortex_tempest,
         :arrandale,
         :atom,
@@ -48,5 +49,28 @@ describe Hardware::CPU do
     it "returns the current CPU's family name as a symbol, or :dunno if it cannot be detected" do
       expect(cpu_families).to include described_class.family
     end
+
+    context "when hw.cpufamily is 0x573b5eec on a Mac", :needs_macos do
+      before do
+        allow(described_class)
+          .to receive(:sysctl_int)
+          .with("hw.cpufamily")
+          .and_return(0x573b5eec)
+      end
+
+      it "returns :arm_firestorm_icestorm on ARM" do
+        allow(described_class).to receive(:arm?).and_return(true)
+        allow(described_class).to receive(:intel?).and_return(false)
+
+        expect(described_class.family).to eq(:arm_firestorm_icestorm)
+      end
+
+      it "returns :westmere on Intel" do
+        allow(described_class).to receive(:arm?).and_return(false)
+        allow(described_class).to receive(:intel?).and_return(true)
+
+        expect(described_class.family).to eq(:westmere)
+      end
+    end
   end
 end