Got rid of a dependent texture read when sampling a lightmap in LW SRP.

ScriptableRenderPipeline/LightweightPipeline/LWRP/ShaderLibrary/Lighting.hlsl

         // Otherwise evaluate SH fully per-pixel
 #endif
 
+
+    #define DECLARE_LIGHTMAP_OR_SH(lmName, shName, index) float2 lmName : TEXCOORD##index
+    #define DECLARE_LIGHTMAP_OR_SH(lmName, shName, index) half3 shName : TEXCOORD##index
     #define OUTPUT_LIGHTMAP_UV(lightmapUV, lightmapScaleOffset, OUT)
     #define OUTPUT_SH(normalWS, OUT) OUT.xyz = SampleSHVertex(normalWS)
 #endif
 // We either sample GI from baked lightmap or from probes.
 // If lightmap: sampleData.xy = lightmapUV
 // If probe: sampleData.xyz = L2 SH terms
-half3 SampleGI(float4 sampleData, half3 normalWS)
+#ifdef LIGHTMAP_ON
+#define SAMPLE_GI(lmName, shName, normalWSName) SampleGI(lmName, normalWSName)
+half3 SampleGI(float2 sampleData, half3 normalWS)
+{
+    return SampleLightmap(sampleData, normalWS);
+}
+#else
+#define SAMPLE_GI(lmName, shName, normalWSName) SampleGI(shName, normalWSName)
+half3 SampleGI(half3 sampleData, half3 normalWS)
-#ifdef LIGHTMAP_ON
-    return SampleLightmap(sampleData.xy, normalWS);
-#endif
-
-    return SampleSHPixel(sampleData.xyz, normalWS);
+    return SampleSHPixel(sampleData, normalWS);
+#endif
 
 half3 GlossyEnvironmentReflection(half3 reflectVector, half perceptualRoughness, half occlusion)
 {

ScriptableRenderPipeline/LightweightPipeline/LWRP/ShaderLibrary/LightweightPassLit.hlsl

 struct LightweightVertexOutput
 {
     float2 uv                       : TEXCOORD0;
-    float4 lightmapUVOrVertexSH     : TEXCOORD1; // holds either lightmapUV or vertex SH. depending on LIGHTMAP_ON
+    DECLARE_LIGHTMAP_OR_SH(lightmapUV, vertexSH, 1);
     float3 posWS                    : TEXCOORD2;
 
 #ifdef _NORMALMAP
 
     inputData.fogCoord = IN.fogFactorAndVertexLight.x;
     inputData.vertexLighting = IN.fogFactorAndVertexLight.yzw;
-    inputData.bakedGI = SampleGI(IN.lightmapUVOrVertexSH, inputData.normalWS);
+    inputData.bakedGI = SAMPLE_GI(IN.lightmapUV, IN.vertexSH, inputData.normalWS);
 }
 
 ///////////////////////////////////////////////////////////////////////////////
     // We either sample GI from lightmap or SH. lightmap UV and vertex SH coefficients
     // are packed in lightmapUVOrVertexSH to save interpolator.
     // The following funcions initialize
-    OUTPUT_LIGHTMAP_UV(v.lightmapUV, unity_LightmapST, o.lightmapUVOrVertexSH);
-    OUTPUT_SH(o.normal.xyz, o.lightmapUVOrVertexSH);
+    OUTPUT_LIGHTMAP_UV(v.lightmapUV, unity_LightmapST, o.lightmapUV);
+    OUTPUT_SH(o.normal.xyz, o.vertexSH);
 
     half3 vertexLight = VertexLighting(o.posWS, o.normal.xyz);
     half fogFactor = ComputeFogFactor(o.clipPos.z);