shader compiler: Ensure all clip distances are initialized when used

Thank you to Ryujinx (riperiperi specifically) for the pointer towards clip distances
Huge thanks to crueter for finding where the code works and Camille for giving pointers along the way.

src/shader_recompiler/backend/spirv/emit_spirv_context_get_set.cpp

@@ -53,6 +53,15 @@ std::optional<OutAttr> OutputAttrPointer(EmitContext& ctx, IR::Attribute attr) {
             return OutputAccessChain(ctx, ctx.output_f32, info.id, index_id);
         }
     }
+
+    for (u32 i = 0; i < ctx.profile.max_user_clip_distances; ++i) {
+        if (!clip_distance_written.test(i)) {
+            const Id idx = ctx.Const(i);
+            const Id element = OutputAccessChain(ctx, ctx.output_f32, ctx.clip_distances, idx);
+            ctx.OpStore(element, ctx.Const(0.0f));
+        }
+    }
+
     switch (attr) {
     case IR::Attribute::PointSize:
         return ctx.output_point_size;
@@ -421,6 +430,14 @@ void EmitSetAttribute(EmitContext& ctx, IR::Attribute attr, Id value, [[maybe_un
     if (Sirit::ValidId(output->type)) {
         value = ctx.OpBitcast(output->type, value);
     }
+
+    static constexpr IR::Attribute cd0 = IR::Attribute::ClipDistance0;
+    static constexpr IR::Attribute cd7 = IR::Attribute::ClipDistance7;
+
+    if (attr >= cd0 && attr <= cd7) {
+        const u32 idx = (u32) attr - (u32) cd0;
+        clip_distance_written.set(idx);
+    }
     ctx.OpStore(output->pointer, value);
 }
 

src/shader_recompiler/backend/spirv/emit_spirv_special.cpp

@@ -108,7 +108,7 @@ void EmitPrologue(EmitContext& ctx) {
                 ctx.OpStore(element_info.id, value);
                 element += num;
             }
-        }
+        }        
     }
     if (ctx.stage == Stage::VertexB || ctx.stage == Stage::Geometry) {
         SetFixedPipelinePointSize(ctx);

src/shader_recompiler/backend/spirv/spirv_emit_context.h

@@ -15,6 +15,8 @@
 
 namespace Shader::Backend::SPIRV {
 
+std::bitset<8> clip_distance_written;
+
 using Sirit::Id;
 
 class VectorTypes {