Fix scalar to array conversion for tessellation factors (#7837)

* Fix scalar to array conversion for tessellation factors in GLSL legalization

Add scalar-to-array conversion support in adaptType() function to handle
cases where users declare scalar tessellation factors (e.g., float TessLevelInner)
but GLSL requires arrays (float[2] for gl_TessLevelInner). This prevents the
generation of BuiltinCast instructions that crash the SPIR-V emitter.

Fixes crash: "unimplemented: Unhandled local inst in spirv-emit: BuiltinCast"

- Add scalar-to-array case in slang-ir-glsl-legalize.cpp adaptType()
- Fill all array elements with the scalar value for tessellation factors
- Add test case for scalar tessellation factor conversion

Fixes #7000

Co-authored-by: Yong He <csyonghe@users.noreply.github.com>

* Apply review feedback fixes

- Change test directive to TEST:SIMPLE
- Use IRArrayType instead of IRArrayTypeBase
- Use MakeArrayFromElement for cleaner scalar-to-array conversion

Co-authored-by: Yong He <csyonghe@users.noreply.github.com>

* Fix type conversion in scalar-to-array tessellation factor conversion

Convert scalar value to array element type before creating array to handle
cases where scalar type differs from array element type (e.g., int to float[3]).

Co-authored-by: Yong He <csyonghe@users.noreply.github.com>

* Use CHECK-DAG for order-independent tessellation factor checks

Co-authored-by: Yong He <csyonghe@users.noreply.github.com>

---------

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Yong He <csyonghe@users.noreply.github.com>

2 files changed, 64 insertions, 0 deletions

diff --git a/source/slang/slang-ir-glsl-legalize.cpp b/source/slang/slang-ir-glsl-legalize.cpp
index f001384a4..ac4d5c336 100644
--- a/source/slang/slang-ir-glsl-legalize.cpp
+++ b/source/slang/slang-ir-glsl-legalize.cpp
@@ -2094,6 +2094,18 @@ ScalarizedVal adaptType(IRBuilder* builder, IRInst* val, IRType* toType, IRType*
             }
         }
     }
+    else if (auto toArray = as<IRArrayType>(toType))
+    {
+        // Handle scalar-to-array conversion for tessellation factors
+        if (as<IRBasicType>(fromType))
+        {
+            // Convert the scalar value to the array's element type first
+            auto arrayElementType = toArray->getElementType();
+            auto convertedVal = builder->emitCast(arrayElementType, val);
+            val = builder->emitMakeArrayFromElement(toType, convertedVal);
+            return ScalarizedVal::value(val);
+        }
+    }
     // TODO: actually consider what needs to go on here...
     return ScalarizedVal::value(builder->emitCast(toType, val));
 }
diff --git a/tests/pipeline/tessellation/scalar-tessellation-factor.slang b/tests/pipeline/tessellation/scalar-tessellation-factor.slang
new file mode 100644
index 000000000..9fc97732d
--- /dev/null
+++ b/tests/pipeline/tessellation/scalar-tessellation-factor.slang
@@ -0,0 +1,52 @@
+//TEST:SIMPLE(filecheck=CHECK): -target spirv -stage hull -entry hullMain -warnings-disable 39001
+
+// Test for issue #7000: scalar tessellation factors should convert to arrays properly
+
+struct VSOutput
+{
+    float4 Pos : SV_POSITION;
+    float3 Normal;
+    float2 UV;
+};
+
+struct HSOutput
+{
+    float4 Pos : SV_POSITION;
+    float3 Normal;
+    float2 UV;
+};
+
+struct ConstantsHSOutput
+{
+    float TessLevelOuter[3] : SV_TessFactor;
+    float TessLevelInner : SV_InsideTessFactor;  // Scalar (should convert to float[2] for GLSL)
+};
+
+ConstantsHSOutput ConstantsHS()
+{
+    ConstantsHSOutput output;
+    output.TessLevelInner = 4.0;
+    output.TessLevelOuter[0] = 4.0;
+    output.TessLevelOuter[1] = 4.0;
+    output.TessLevelOuter[2] = 4.0;
+    return output;
+}
+
+[shader("hull")]
+[domain("tri")]
+[partitioning("integer")]
+[outputtopology("triangle_cw")]
+[outputcontrolpoints(3)]
+[patchconstantfunc("ConstantsHS")]
+HSOutput hullMain(InputPatch<VSOutput, 3> patch, uint InvocationID: SV_OutputControlPointID)
+{
+    HSOutput output;
+    output.Pos = patch[InvocationID].Pos;
+    output.Normal = patch[InvocationID].Normal;
+    output.UV = patch[InvocationID].UV;
+    return output;
+}
+
+// CHECK: OpExecutionMode
+// CHECK-DAG: OpDecorate {{.*}} BuiltIn TessLevelInner
+// CHECK-DAG: OpDecorate {{.*}} BuiltIn TessLevelOuter
\ No newline at end of file