Check if debugVar for is debuggable types in the legalization pass (#8326)

## Problem
When generic functions with debug variables were specialized with
concrete types containing non-debuggable fields (e.g.,
`StructuredBuffer`), the IR cloning process would create invalid
`DebugVar` instructions without checking if the substituted types
remained debuggable.

## Solution
This fix adds a defensive check in the legalization pass that removes
the debugVar created for the non-debuggable types.

---------

Co-authored-by: slangbot <ellieh+slangbot@nvidia.com>
Co-authored-by: slangbot <186143334+slangbot@users.noreply.github.com>

1 files changed, 62 insertions, 0 deletions

diff --git a/tests/spirv/debug-var-generic-param.slang b/tests/spirv/debug-var-generic-param.slang
new file mode 100644
index 000000000..85049eefe
--- /dev/null
+++ b/tests/spirv/debug-var-generic-param.slang
@@ -0,0 +1,62 @@
+//TEST:SIMPLE(filecheck=CHECK):-target spirv -entry main -stage compute -g2 -emit-spirv-directly
+
+// Test for debug variable handling with generic parameters and structs containing resources
+// This test ensures that structs containing StructuredBuffer fields don't get invalid DebugVar instructions
+
+StructuredBuffer<uint4> gData;
+
+interface IGeometryReader
+{
+    float4 read(uint attributeIndex);
+}
+
+struct PositionReader : IGeometryReader
+{
+    float4 read(uint vertexIndex)
+    {
+        return m_geometryBuffer[vertexIndex];
+    }
+
+    __init(StructuredBuffer<uint4> geometryBuffer)
+    {
+        m_geometryBuffer = geometryBuffer;
+    }
+
+    StructuredBuffer<uint4> m_geometryBuffer;
+}
+
+float4 test<Reader: IGeometryReader>(Reader reader)
+{
+    float4 pos = reader.read(0);
+    return pos;
+}
+
+RWStructuredBuffer<float4> result;
+
+[numthreads(1,1,1)]
+void main()
+{
+    let reader = PositionReader(gData);
+    float4 pos = test(reader);
+    
+    result[0] = pos;
+}
+
+// Verify that debug info is generated but no invalid DebugVar for struct with StructuredBuffer
+// CHECK: OpExtInst %void {{.*}} DebugExpression
+
+// Ensure we have the expected legitimate debug variables
+// CHECK: pos{{.*}}DebugLocalVariable{{.*}}
+// CHECK: vertexIndex{{.*}}DebugLocalVariable{{.*}}
+
+// After legitimate debug vars, ensure we don't create debug vars for non-debuggable types
+// Specifically check that we don't create debug vars for variables containing StructuredBuffer:
+// - No debug var for 'reader' (PositionReader struct instance)
+// - No debug var for 'm_geometryBuffer' (StructuredBuffer field)
+// The absence of these variables in the output proves the fix is working
+// CHECK-NOT: reader{{.*}}DebugLocalVariable{{.*}}
+// CHECK-NOT: m_geometryBuffer{{.*}}DebugLocalVariable{{.*}}
+// CHECK-NOT: geometryBuffer{{.*}}DebugLocalVariable{{.*}}
+
+// Verify the function ends properly
+// CHECK: OpFunctionEnd
\ No newline at end of file