SpirvShader: Implement GLSLstd450Pow

Bug: b/126873455
Tests: dEQP-VK.glsl.builtin.precision.pow.*
Change-Id: I74797e69adc78e4c06ec4a8b2923b78166afbc18
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/28439
Tested-by: Ben Clayton <bclayton@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
diff --git a/src/Reactor/LLVMReactor.cpp b/src/Reactor/LLVMReactor.cpp
index 46abd51..c04b300 100644
--- a/src/Reactor/LLVMReactor.cpp
+++ b/src/Reactor/LLVMReactor.cpp
@@ -566,6 +566,7 @@
 			func_.emplace("acoshf", reinterpret_cast<void*>(acoshf));
 			func_.emplace("atanhf", reinterpret_cast<void*>(atanhf));
 			func_.emplace("atan2f", reinterpret_cast<void*>(atan2f));
+			func_.emplace("powf", reinterpret_cast<void*>(powf));
 
 #ifdef __APPLE__
 			// LLVM uses this function on macOS for tan.
@@ -3174,6 +3175,13 @@
 		return RValue<Float4>(V(out));
 	}
 
+	RValue<Float4> Pow(RValue<Float4> x, RValue<Float4> y)
+	{
+		auto func = llvm::Intrinsic::getDeclaration(::module, llvm::Intrinsic::pow,
+			{ T(Float4::getType()), T(Float4::getType()) } );
+		return RValue<Float4>(V(::builder->CreateCall(func, { V(x.value), V(y.value) })));
+	}
+
 	Type *Float4::getType()
 	{
 		return T(llvm::VectorType::get(T(Float::getType()), 4));