Some shuffling around reduces frame time on older devices.

ScriptableRenderPipeline/LightweightPipeline/LWRP/ShaderLibrary/Lighting.hlsl

 {
     half3 halfVec = SafeNormalize(lightDir + viewDir);
     half NdotH = saturate(dot(normal, halfVec));
-    half3 specularReflection = specularGloss.rgb * pow(NdotH, shininess) * specularGloss.a;
+    half modifier = pow(NdotH, shininess) * specularGloss.a;
+    half3 specularReflection = specularGloss.rgb * modifier;
     return lightColor * specularReflection;
 }
 
     }
 #endif
 
-    half3 finalColor = diffuseColor * diffuse + emission;
-    finalColor += inputData.vertexLighting * diffuse;
+    half3 fullDiffuse = diffuseColor + inputData.vertexLighting;
+    half3 finalColor = fullDiffuse * diffuse + emission;
     
 #if defined(_SPECGLOSSMAP) || defined(_SPECULAR_COLOR)
     finalColor += specularColor;

ScriptableRenderPipeline/LightweightPipeline/LWRP/ShaderLibrary/LightweightPassLit.hlsl

 {
     float2 uv                       : TEXCOORD0;
     DECLARE_LIGHTMAP_OR_SH(lightmapUV, vertexSH, 1);
-    float3 posWS                    : TEXCOORD2;
+    float4 posWSShininess           : TEXCOORD2;    // xyz: posWS, w: Shininess * 128
 
 #ifdef _NORMALMAP
     half4 normal                    : TEXCOORD3;    // xyz: normal, w: viewDir.x
 
 void InitializeInputData(LightweightVertexOutput IN, half3 normalTS, out InputData inputData)
 {
-    inputData.positionWS = IN.posWS.xyz;
+    inputData.positionWS = IN.posWSShininess.xyz;
 
 #ifdef _NORMALMAP
     half3 viewDir = half3(IN.normal.w, IN.tangent.w, IN.binormal.w);
 
     o.uv = TRANSFORM_TEX(v.texcoord, _MainTex);
 
-    o.posWS = TransformObjectToWorld(v.vertex.xyz);
-    o.clipPos = TransformWorldToHClip(o.posWS);
+    o.posWSShininess.xyz = TransformObjectToWorld(v.vertex.xyz);
+    o.posWSShininess.w = _Shininess * 128.0;
+    o.clipPos = TransformWorldToHClip(o.posWSShininess.xyz);
-    half3 viewDir = GetCameraPositionWS() - o.posWS;
+    half3 viewDir = GetCameraPositionWS() - o.posWSShininess.xyz;
 #if !SHADER_HINT_NICE_QUALITY
     // Normalize in vertex and avoid renormalizing it in frag to save ALU.
     viewDir = SafeNormalize(viewDir);
     OUTPUT_LIGHTMAP_UV(v.lightmapUV, unity_LightmapST, o.lightmapUV);
     OUTPUT_SH(o.normal.xyz, o.vertexSH);
 
-    half3 vertexLight = VertexLighting(o.posWS, o.normal.xyz);
+    half3 vertexLight = VertexLighting(o.posWSShininess.xyz, o.normal.xyz);
     half fogFactor = ComputeFogFactor(o.clipPos.z);
     o.fogFactorAndVertexLight = half4(fogFactor, vertexLight);
     o.shadowCoord = ComputeShadowCoord(o.clipPos);
 
     half3 emission = Emission(uv);
     half4 specularGloss = SpecularGloss(uv, diffuseAlpha.a);
-    half shininess = _Shininess * 128.0h;
+    half shininess = IN.posWSShininess.w;
 
     InputData inputData;
     InitializeInputData(IN, normalTS, inputData);

ScriptableRenderPipeline/LightweightPipeline/LWRP/ShaderLibrary/LightweightPassShadow.hlsl

     float scale = invNdotL * _ShadowBias.y;
 
     // normal bias is negative since we want to apply an inset normal offset
-    o.posWS = o.normal * scale.xxx + o.posWS;
-    float4 clipPos = TransformWorldToHClip(o.posWS);
+    o.posWSShininess.xyz = o.normal * scale.xxx + o.posWSShininess.xyz;
+    float4 clipPos = TransformWorldToHClip(o.posWSShininess.xyz);
 
     // _ShadowBias.x sign depens on if platform has reversed z buffer
     clipPos.z += _ShadowBias.x;