SpirvShader: Implement GLSLstd450Tan

Bug: b/126873455
Tests: dEQP-VK.glsl.builtin.precision.tan.*
Change-Id: I229b46b285075bd25272145a562135df08438160
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/28670
Presubmit-Ready: Ben Clayton <bclayton@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Chris Forbes <chrisforbes@google.com>
Tested-by: Chris Forbes <chrisforbes@google.com>
diff --git a/src/Reactor/LLVMReactor.cpp b/src/Reactor/LLVMReactor.cpp
index 578dfa1..f7ad721 100644
--- a/src/Reactor/LLVMReactor.cpp
+++ b/src/Reactor/LLVMReactor.cpp
@@ -556,6 +556,13 @@
 			func_.emplace("fmodf", reinterpret_cast<void*>(fmodf));
 			func_.emplace("sinf", reinterpret_cast<void*>(sinf));
 			func_.emplace("cosf", reinterpret_cast<void*>(cosf));
+
+#ifdef __APPLE__
+			// LLVM uses this function on macOS for tan.
+			func_.emplace("sincosf_stret", reinterpret_cast<void*>(__sincosf_stret));
+#elif defined(__linux__)
+			func_.emplace("sincosf", reinterpret_cast<void*>(sincosf));
+#endif // __APPLE__
 		}
 
 		void *findSymbol(const std::string &name) const
@@ -3077,6 +3084,11 @@
 		return RValue<Float4>(V(::builder->CreateCall(func, V(v.value))));
 	}
 
+	RValue<Float4> Tan(RValue<Float4> v)
+	{
+		return Sin(v) / Cos(v);
+	}
+
 	Type *Float4::getType()
 	{
 		return T(llvm::VectorType::get(T(Float::getType()), 4));