Add fallback CPU detection when llvm is not aware of the CPU model

Utilities/JIT.h

@@ -495,6 +495,7 @@ namespace llvm
 	class LLVMContext;
 	class ExecutionEngine;
 	class Module;
+	class StringRef;
 }
 
 // Temporary compiler interface
@@ -560,4 +561,6 @@ public:
 	bool add_sub_disk_space(ssz space);
 };
 
+llvm::StringRef fallback_cpu_detection();
+
 #endif // LLVM_AVAILABLE

Utilities/JITLLVM.cpp

@@ -440,6 +440,12 @@ std::string jit_compiler::cpu(const std::string& _cpu)
 	{
 		m_cpu = llvm::sys::getHostCPUName().str();
 
+		if (m_cpu == "generic")
+		{
+			// Try to detect a best match based on other criteria
+			m_cpu = fallback_cpu_detection();
+		}
+
 		if (m_cpu == "sandybridge" ||
 			m_cpu == "ivybridge" ||
 			m_cpu == "haswell" ||
@@ -717,4 +723,49 @@ u64 jit_compiler::get(const std::string& name)
 	return m_engine->getGlobalValueAddress(name);
 }
 
+llvm::StringRef fallback_cpu_detection()
+{
+#if defined (ARCH_X64)
+	// If we got here we either have a very old and outdated CPU or a new CPU that has not been seen by LLVM yet.
+	llvm::StringRef brand = utils::get_cpu_brand();
+	const auto family = utils::get_cpu_family();
+	const auto model = utils::get_cpu_model();
+
+	if (brand.startswith("AMD"))
+	{
+		switch (family)
+		{
+		case 0x17:
+		case 0x18:
+			// No major differences between znver1 and znver2, return the lesser
+			return "znver1";
+		case 0x19:
+			// Models 0-Fh are zen3 as are 20h-60h. The rest we can assume are zen4
+			return ((model >= 0x20 && model <= 0x60) || model < 0x10)
+				? "znver3"
+				: "znver4";
+		case 0x1a:
+			// Only one generation in family 1a so far
+			return "znver5";
+		default:
+			return "znver5"; // Return newest known model here
+		}
+	}
+	else if (brand.startswith("Virtual Apple"))
+	{
+		// No AVX. This will change in MacOS 15+, at which point we may revise this.
+		return "nehalem";
+	}
+
+#elif defined(ARCH_ARM64)
+	// TODO: Read the data from /proc/cpuinfo. ARM CPU registers are not accessible from usermode.
+	// This will be a pain when supporting snapdragon on windows but we'll cross that bridge when we get there.
+	// Require at least armv8-2a. Older chips are going to be useless anyway.
+	return "cortex-a78";
+#endif
+
+	// Failed to guess, use generic fallback
+	return "generic";
+}
+
 #endif // LLVM_AVAILABLE

rpcs3/Emu/CPU/CPUTranslator.cpp

@@ -90,7 +90,13 @@ void cpu_translator::initialize(llvm::LLVMContext& context, llvm::ExecutionEngin
 	m_context = context;
 	m_engine = &engine;
 
-	const auto cpu = m_engine->getTargetMachine()->getTargetCPU();
+	auto cpu = m_engine->getTargetMachine()->getTargetCPU();
+
+	if (cpu == "generic")
+	{
+		// Detection failed, try to guess
+		cpu = fallback_cpu_detection();
+	}
 
 	// Test SSSE3 feature (TODO)
 	if (cpu == "generic" ||