[vulkan, spirv] Fall back to scalar warp intrinsics in the geometry stage when unsupported

src/shader_recompiler/backend/spirv/emit_spirv.cpp

@@ -440,7 +440,8 @@ void SetupCapabilities(const Profile& profile, const Info& info, EmitContext& ct
     }
     if ((info.uses_subgroup_vote || info.uses_subgroup_invocation_id ||
          info.uses_subgroup_shuffles) &&
-        profile.support_vote && profile.SupportsSubgroupStage(ctx.stage)) {
+        profile.support_vote &&
+        (ctx.stage != Stage::Geometry || profile.support_subgroup_in_geometry_stage)) {
         ctx.AddCapability(spv::Capability::GroupNonUniformBallot);
         ctx.AddCapability(spv::Capability::GroupNonUniformShuffle);
         if (!profile.warp_size_potentially_larger_than_guest) {

src/shader_recompiler/backend/spirv/emit_spirv_warp.cpp

@@ -13,6 +13,18 @@ Id SubgroupScope(EmitContext& ctx) {
     return ctx.Const(static_cast<u32>(spv::Scope::Subgroup));
 }
 
+// Some mobile GPUs (e.g. Adreno/Turnip) only advertise subgroup ballot/shuffle support for the
+// fragment and compute stages (VkPhysicalDeviceSubgroupProperties::supportedStages), even though
+// they support these operations elsewhere. Guest shaders that use VOTE/SHFL in a geometry program
+// would otherwise emit GroupNonUniform* SPIR-V the driver never declared support for in that
+// stage. There is no barrier in the geometry stage, so a real cross-invocation emulation can't be
+// made correct; instead, treat the current invocation as if it were alone in its subgroup. This is
+// semantically wrong for guest code that relies on genuine cross-lane communication, but it is
+// well-defined, valid SPIR-V that doesn't depend on unsupported hardware capabilities.
+bool NeedsGeometrySubgroupFallback(EmitContext& ctx) {
+    return ctx.stage == Stage::Geometry && !ctx.profile.support_subgroup_in_geometry_stage;
+}
+
 bool StageSupportsSubgroups(EmitContext& ctx) {
     return ctx.profile.SupportsSubgroupStage(ctx.stage);
 }
@@ -94,6 +106,9 @@ Id AddPartitionBase(EmitContext& ctx, Id thread_id) {
 } // Anonymous namespace
 
 Id EmitLaneId(EmitContext& ctx) {
+    if (NeedsGeometrySubgroupFallback(ctx)) {
+        return ctx.u32_zero_value;
+    }
     const Id id{GetThreadId(ctx)};
     if (!ctx.profile.warp_size_potentially_larger_than_guest) {
         return id;
@@ -102,6 +117,9 @@ Id EmitLaneId(EmitContext& ctx) {
 }
 
 Id EmitVoteAll(EmitContext& ctx, Id pred) {
+    if (NeedsGeometrySubgroupFallback(ctx)) {
+        return pred;
+    }
     if (!StageSupportsSubgroups(ctx)) {
         return pred;
     }
@@ -118,6 +136,9 @@ Id EmitVoteAll(EmitContext& ctx, Id pred) {
 }
 
 Id EmitVoteAny(EmitContext& ctx, Id pred) {
+    if (NeedsGeometrySubgroupFallback(ctx)) {
+        return pred;
+    }
     if (!StageSupportsSubgroups(ctx)) {
         return pred;
     }
@@ -134,6 +155,9 @@ Id EmitVoteAny(EmitContext& ctx, Id pred) {
 }
 
 Id EmitVoteEqual(EmitContext& ctx, Id pred) {
+    if (NeedsGeometrySubgroupFallback(ctx)) {
+        return ctx.true_value;
+    }
     if (!StageSupportsSubgroups(ctx)) {
         return ctx.true_value;
     }
@@ -151,6 +175,16 @@ Id EmitVoteEqual(EmitContext& ctx, Id pred) {
 }
 
 Id EmitSubgroupBallot(EmitContext& ctx, Id pred) {
+    if (NeedsGeometrySubgroupFallback(ctx)) {
+        // Reflect only this invocation's own predicate. There is no way to observe other
+        // invocations' predicates without real subgroup hardware support in this stage, so this
+        // is a best-effort approximation: it keeps any branch gated on "did anyone match" live
+        // (rather than letting the SPIR-V optimizer prove it dead, which previously caused
+        // indirect draws fed by this shader to see indexCount=instanceCount=0), but any downstream
+        // math that assumes a real cross-lane population count (e.g. popcount-based compaction
+        // offsets) will not be correct.
+        return ctx.OpSelect(ctx.U32[1], pred, ctx.Const(1U), ctx.u32_zero_value);
+    }
     if (!StageSupportsSubgroups(ctx)) {
         return ctx.OpSelect(ctx.U32[1], pred, ctx.Const(1u), ctx.u32_zero_value);
     }
@@ -162,6 +196,9 @@ Id EmitSubgroupBallot(EmitContext& ctx, Id pred) {
 }
 
 Id EmitSubgroupEqMask(EmitContext& ctx) {
+    if (NeedsGeometrySubgroupFallback(ctx)) {
+        return ctx.Const(1U);
+    }
     if (!StageSupportsSubgroups(ctx)) {
         return ctx.Const(1u);
     }
@@ -169,6 +206,9 @@ Id EmitSubgroupEqMask(EmitContext& ctx) {
 }
 
 Id EmitSubgroupLtMask(EmitContext& ctx) {
+    if (NeedsGeometrySubgroupFallback(ctx)) {
+        return ctx.u32_zero_value;
+    }
     if (!StageSupportsSubgroups(ctx)) {
         return ctx.u32_zero_value;
     }
@@ -176,6 +216,9 @@ Id EmitSubgroupLtMask(EmitContext& ctx) {
 }
 
 Id EmitSubgroupLeMask(EmitContext& ctx) {
+    if (NeedsGeometrySubgroupFallback(ctx)) {
+        return ctx.Const(1U);
+    }
     if (!StageSupportsSubgroups(ctx)) {
         return ctx.Const(1u);
     }
@@ -183,6 +226,9 @@ Id EmitSubgroupLeMask(EmitContext& ctx) {
 }
 
 Id EmitSubgroupGtMask(EmitContext& ctx) {
+    if (NeedsGeometrySubgroupFallback(ctx)) {
+        return ctx.u32_zero_value;
+    }
     if (!StageSupportsSubgroups(ctx)) {
         return ctx.u32_zero_value;
     }
@@ -190,6 +236,9 @@ Id EmitSubgroupGtMask(EmitContext& ctx) {
 }
 
 Id EmitSubgroupGeMask(EmitContext& ctx) {
+    if (NeedsGeometrySubgroupFallback(ctx)) {
+        return ctx.Const(1U);
+    }
     if (!StageSupportsSubgroups(ctx)) {
         return ctx.Const(1u);
     }
@@ -198,6 +247,10 @@ Id EmitSubgroupGeMask(EmitContext& ctx) {
 
 Id EmitShuffleIndex(EmitContext& ctx, IR::Inst* inst, Id value, Id index, Id clamp,
                     Id segmentation_mask) {
+    if (NeedsGeometrySubgroupFallback(ctx)) {
+        SetInBoundsFlag(inst, ctx.false_value);
+        return value;
+    }
     const Id not_seg_mask{ctx.OpNot(ctx.U32[1], segmentation_mask)};
     const Id thread_id{EmitLaneId(ctx)};
     const Id min_thread_id{ComputeMinThreadId(ctx, thread_id, segmentation_mask)};
@@ -217,6 +270,10 @@ Id EmitShuffleIndex(EmitContext& ctx, IR::Inst* inst, Id value, Id index, Id cla
 
 Id EmitShuffleUp(EmitContext& ctx, IR::Inst* inst, Id value, Id index, Id clamp,
                  Id segmentation_mask) {
+    if (NeedsGeometrySubgroupFallback(ctx)) {
+        SetInBoundsFlag(inst, ctx.false_value);
+        return value;
+    }
     const Id thread_id{EmitLaneId(ctx)};
     const Id max_thread_id{GetMaxThreadId(ctx, thread_id, clamp, segmentation_mask)};
     Id src_thread_id{ctx.OpISub(ctx.U32[1], thread_id, index)};
@@ -232,6 +289,10 @@ Id EmitShuffleUp(EmitContext& ctx, IR::Inst* inst, Id value, Id index, Id clamp,
 
 Id EmitShuffleDown(EmitContext& ctx, IR::Inst* inst, Id value, Id index, Id clamp,
                    Id segmentation_mask) {
+    if (NeedsGeometrySubgroupFallback(ctx)) {
+        SetInBoundsFlag(inst, ctx.false_value);
+        return value;
+    }
     const Id thread_id{EmitLaneId(ctx)};
     const Id max_thread_id{GetMaxThreadId(ctx, thread_id, clamp, segmentation_mask)};
     Id src_thread_id{ctx.OpIAdd(ctx.U32[1], thread_id, index)};
@@ -247,6 +308,10 @@ Id EmitShuffleDown(EmitContext& ctx, IR::Inst* inst, Id value, Id index, Id clam
 
 Id EmitShuffleButterfly(EmitContext& ctx, IR::Inst* inst, Id value, Id index, Id clamp,
                         Id segmentation_mask) {
+    if (NeedsGeometrySubgroupFallback(ctx)) {
+        SetInBoundsFlag(inst, ctx.false_value);
+        return value;
+    }
     const Id thread_id{EmitLaneId(ctx)};
     const Id max_thread_id{GetMaxThreadId(ctx, thread_id, clamp, segmentation_mask)};
     Id src_thread_id{ctx.OpBitwiseXor(ctx.U32[1], thread_id, index)};

src/shader_recompiler/backend/spirv/spirv_emit_context.cpp

@@ -1455,13 +1455,14 @@ void EmitContext::DefineInputs(const IR::Program& program) {
     if (info.uses_is_helper_invocation) {
         is_helper_invocation = DefineInput(*this, U1, false, spv::BuiltIn::HelperInvocation);
     }
-    if (info.uses_subgroup_mask && profile.SupportsSubgroupStage(stage)) {
+    if (info.uses_subgroup_mask &&
+        (stage != Stage::Geometry || profile.support_subgroup_in_geometry_stage)) {
         subgroup_mask_eq = DefineInput(*this, U32[4], false, spv::BuiltIn::SubgroupEqMaskKHR);
         subgroup_mask_lt = DefineInput(*this, U32[4], false, spv::BuiltIn::SubgroupLtMaskKHR);
         subgroup_mask_le = DefineInput(*this, U32[4], false, spv::BuiltIn::SubgroupLeMaskKHR);
         subgroup_mask_gt = DefineInput(*this, U32[4], false, spv::BuiltIn::SubgroupGtMaskKHR);
         subgroup_mask_ge = DefineInput(*this, U32[4], false, spv::BuiltIn::SubgroupGeMaskKHR);
-        if (stage == Stage::Fragment) {
+        if (profile.support_explicit_workgroup_layout) {
             Decorate(subgroup_mask_eq, spv::Decoration::Flat);
             Decorate(subgroup_mask_lt, spv::Decoration::Flat);
             Decorate(subgroup_mask_le, spv::Decoration::Flat);
@@ -1469,10 +1470,11 @@ void EmitContext::DefineInputs(const IR::Program& program) {
             Decorate(subgroup_mask_ge, spv::Decoration::Flat);
         }
     }
-    if ((info.uses_fswzadd || info.uses_subgroup_invocation_id || info.uses_subgroup_shuffles ||
-         (profile.warp_size_potentially_larger_than_guest &&
-          (info.uses_subgroup_vote || info.uses_subgroup_mask))) &&
-        profile.SupportsSubgroupStage(stage)) {
+    if (info.uses_fswzadd ||
+        ((info.uses_subgroup_invocation_id || info.uses_subgroup_shuffles ||
+          (profile.warp_size_potentially_larger_than_guest &&
+           (info.uses_subgroup_vote || info.uses_subgroup_mask))) &&
+         (stage != Stage::Geometry || profile.support_subgroup_in_geometry_stage))) {
         AddCapability(spv::Capability::GroupNonUniform);
         subgroup_local_invocation_id =
             DefineInput(*this, U32[1], false, spv::BuiltIn::SubgroupLocalInvocationId);

src/shader_recompiler/profile.h

@@ -41,6 +41,12 @@ struct Profile {
     bool support_quad_shuffles{};
     bool support_vote{};
     u32 supported_subgroup_stages{0x7F};
+    bool support_subgroup_in_geometry_stage{}; ///< True when the device advertises subgroup
+                                               ///< ballot/shuffle support for VK_SHADER_STAGE_GEOMETRY_BIT
+                                               ///< (VkPhysicalDeviceSubgroupProperties::supportedStages).
+                                               ///< Many mobile GPUs support subgroup ops only in
+                                               ///< fragment/compute; guest shaders using VOTE/SHFL in a
+                                               ///< geometry program need a non-subgroup fallback there.
     bool support_viewport_index_layer_non_geometry{};
     bool support_viewport_mask{};
     bool support_typeless_image_loads{};

src/video_core/renderer_vulkan/vk_pipeline_cache.cpp

@@ -410,6 +410,11 @@ PipelineCache::PipelineCache(Tegra::MaxwellDeviceMemoryManager& device_memory_,
         .support_quad_shuffles = device.IsSubgroupFeatureSupported(VK_SUBGROUP_FEATURE_QUAD_BIT),
         .support_vote = device.IsSubgroupFeatureSupported(VK_SUBGROUP_FEATURE_VOTE_BIT),
         .supported_subgroup_stages = supported_subgroup_stages,
+        .support_subgroup_in_geometry_stage =
+            device.IsSubgroupFeatureSupported(VK_SUBGROUP_FEATURE_VOTE_BIT) &&
+            device.IsSubgroupFeatureSupported(VK_SUBGROUP_FEATURE_BALLOT_BIT) &&
+            device.IsSubgroupFeatureSupported(VK_SUBGROUP_FEATURE_SHUFFLE_BIT) &&
+            device.IsSubgroupFeatureSupportedInStage(VK_SHADER_STAGE_GEOMETRY_BIT),
         .support_viewport_index_layer_non_geometry =
             device.IsExtShaderViewportIndexLayerSupported(),
         .support_viewport_mask = device.IsNvViewportArray2Supported(),

src/video_core/vulkan_common/vulkan_device.h

@@ -479,6 +479,11 @@ FN_MAX_LIMIT_LIST
         return properties.subgroup_properties.supportedStages;
     }
 
+    /// Returns true if the device supports subgroup ballot/shuffle in the given shader stage.
+    bool IsSubgroupFeatureSupportedInStage(VkShaderStageFlagBits stage) const {
+        return properties.subgroup_properties.supportedStages & stage;
+    }
+
     /// Returns the maximum number of push descriptors.
     u32 MaxPushDescriptors() const {
         return properties.push_descriptor.maxPushDescriptors;