From 3d0f5ee55788dca324641ae9268ee37dc4d7d9d5 Mon Sep 17 00:00:00 2001
From: "Harsh Aggarwal (NVIDIA)" <haaggarwal@nvidia.com>
Date: Wed, 10 Sep 2025 17:31:36 +0530
Subject: CUDA: Fix compiler crash with unsized array field -
 nonuniformres-as-… (#8380)
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…function-parameter.slang #8315

Root Cause:
CUDA compilation crashed with `assert failure:
!seenFinalUnsizedArrayField` because unsized arrays like
`RWStructuredBuffer<uint> globalBuffer[]` were not the final field in
generated parameter structs, violating the layout constraint in
slang-ir-layout.cpp.

Fix:
Extended `collectGlobalUniformParameters` to automatically reorder
struct fields for CUDA targets - regular fields first, unsized arrays
last. Other targets preserve original order.

Impact:
- Enables CUDA support for nonuniform resource indexing as function
parameters
- Zero impact on existing GLSL/HLSL/SPIRV targets
- Automatic handling - no manual parameter reordering required

Files: slang-emit.cpp, slang-ir-collect-global-uniforms.cpp/.h, test
file

---------

Co-authored-by: slangbot <ellieh+slangbot@nvidia.com>
Co-authored-by: slangbot <186143334+slangbot@users.noreply.github.com>
Co-authored-by: Ellie Hermaszewska <ellieh@nvidia.com>
---
 source/slang/slang-emit.cpp                       |  2 +-
 source/slang/slang-ir-collect-global-uniforms.cpp | 49 ++++++++++++++++++++++-
 source/slang/slang-ir-collect-global-uniforms.h   |  5 ++-
 3 files changed, 52 insertions(+), 4 deletions(-)

(limited to 'source/slang')

diff --git a/source/slang/slang-emit.cpp b/source/slang/slang-emit.cpp
index f5b818c5d..31e6d17be 100644
--- a/source/slang/slang-emit.cpp
+++ b/source/slang/slang-emit.cpp
@@ -802,7 +802,7 @@ Result linkAndOptimizeIR(
     // can assume that all ordinary/uniform data is strictly
     // passed using constant buffers.
     //
-    collectGlobalUniformParameters(irModule, outLinkedIR.globalScopeVarLayout);
+    collectGlobalUniformParameters(irModule, outLinkedIR.globalScopeVarLayout, target);
 #if 0
     dumpIRIfEnabled(codeGenContext, irModule, "GLOBAL UNIFORMS COLLECTED");
 #endif
diff --git a/source/slang/slang-ir-collect-global-uniforms.cpp b/source/slang/slang-ir-collect-global-uniforms.cpp
index fb2a2233c..aad0de44f 100644
--- a/source/slang/slang-ir-collect-global-uniforms.cpp
+++ b/source/slang/slang-ir-collect-global-uniforms.cpp
@@ -49,6 +49,7 @@ struct CollectGlobalUniformParametersContext
     //
     IRModule* module;
     IRVarLayout* globalScopeVarLayout;
+    CodeGenTarget target = CodeGenTarget::Unknown;
 
     IRGlobalParam* _getGlobalParamFromLayoutFieldKey(IRInst* key)
     {
@@ -174,7 +175,47 @@ struct CollectGlobalUniformParametersContext
         // parameters that were present in the layout information (they are
         // represented as the fields of the global-scope `struct` layout).
         //
-        for (auto fieldLayoutAttr : globalParamsStructTypeLayout->getFieldLayoutAttrs())
+        // For CUDA targets, we need to ensure unsized arrays come last to satisfy
+        // the layout constraint in slang-ir-layout.cpp
+        auto fieldAttrs = globalParamsStructTypeLayout->getFieldLayoutAttrs();
+
+        // Create ordered field list - for CUDA, put unsized arrays last
+        List<IRStructFieldLayoutAttr*> orderedFields;
+
+        if (target == CodeGenTarget::CUDASource)
+        {
+            // For CUDA: separate regular and unsized array fields
+            List<IRStructFieldLayoutAttr*> regularFields;
+            List<IRStructFieldLayoutAttr*> unsizedArrayFields;
+
+            for (auto fieldLayoutAttr : fieldAttrs)
+            {
+                auto globalParam =
+                    _getGlobalParamFromLayoutFieldKey(fieldLayoutAttr->getFieldKey());
+                if (globalParam && as<IRUnsizedArrayType>(globalParam->getDataType()))
+                {
+                    unsizedArrayFields.add(fieldLayoutAttr);
+                }
+                else
+                {
+                    regularFields.add(fieldLayoutAttr);
+                }
+            }
+
+            // Add regular fields first, then unsized arrays
+            for (auto field : regularFields)
+                orderedFields.add(field);
+            for (auto field : unsizedArrayFields)
+                orderedFields.add(field);
+        }
+        else
+        {
+            // For other targets: preserve original order
+            for (auto field : fieldAttrs)
+                orderedFields.add(field);
+        }
+
+        for (auto fieldLayoutAttr : orderedFields)
         {
             // We expect the IR layout pass to have encoded field per-field
             // layout so that the "key" for the field is the corresponding
@@ -339,11 +380,15 @@ struct CollectGlobalUniformParametersContext
     }
 };
 
-void collectGlobalUniformParameters(IRModule* module, IRVarLayout* globalScopeVarLayout)
+void collectGlobalUniformParameters(
+    IRModule* module,
+    IRVarLayout* globalScopeVarLayout,
+    CodeGenTarget target)
 {
     CollectGlobalUniformParametersContext context;
     context.module = module;
     context.globalScopeVarLayout = globalScopeVarLayout;
+    context.target = target;
 
     context.processModule();
 }
diff --git a/source/slang/slang-ir-collect-global-uniforms.h b/source/slang/slang-ir-collect-global-uniforms.h
index 76f56f074..5f9393a9b 100644
--- a/source/slang/slang-ir-collect-global-uniforms.h
+++ b/source/slang/slang-ir-collect-global-uniforms.h
@@ -11,6 +11,9 @@ struct IRVarLayout;
 /// Collect global-scope shader parameters that use uniform/ordinary
 /// storage into a single `struct` (possibly wrapped in a constant buffer).
 ///
-void collectGlobalUniformParameters(IRModule* module, IRVarLayout* globalScopeVarLayout);
+void collectGlobalUniformParameters(
+    IRModule* module,
+    IRVarLayout* globalScopeVarLayout,
+    CodeGenTarget target = CodeGenTarget::Unknown);
 
 } // namespace Slang
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