Legalize type as well in legalizeOperand (#8483)

This fixes a type mismatch issue. See the generated cuda code

```cuda
struct Query_0
{
    EmptyExample_0 query_0;
    uint hasNonEmptyAbsorbingBoundary_0;
};

struct Query_1
{
    uint hasNonEmptyAbsorbingBoundary_0;
};

struct GlobalParams_0
{
    Query_0* gQuery_0;
    RWStructuredBuffer<float3 > gInput_0;
    RWStructuredBuffer<float> gOutput_0;
};

...
Query_1 _S4 = *globalParams_0->gQuery_0;      // ==> type mismatch at call site!

```

**Root Cause:** During the empty type legalization pass in Slang's IR
processing, struct types were being optimized. e.g., `Query_0` →
`Query_1` with empty type removed), but this created an inconsistency:

**Function parameters were updated:** When Query_compute_0 function was
legalized, its parameter type was correctly updated from `Query_0` to
the optimized `Query_1`

**Global parameter types were NOT updated:** The
`ParameterBlock<Struct>` type in globalParams still referenced the old
`Query_0` type

The PR adds special handling for type operands in the `legalizeInst`
function. This triggers the legalization of the `StructType` from the
original `legalizeOperand` call site. The leaglized result will be saved
in the type-to-legal-type map and be re-used when the same type requires
legalization again (e.g. in the `IRFunc` as parameter)

Fixes: https://github.com/shader-slang/slang/issues/7905

1 files changed, 63 insertions, 0 deletions

diff --git a/tests/bugs/gh-7905.slang b/tests/bugs/gh-7905.slang
new file mode 100644
index 000000000..69dd6d3ba
--- /dev/null
+++ b/tests/bugs/gh-7905.slang
@@ -0,0 +1,63 @@
+//TEST:SIMPLE(filecheck=CHECK): -target cuda -entry runPointEstimator
+
+// Test for issue #7905: CUDA Backend failure due to type mismatch
+// This test ensures that struct types in ParameterBlock operands are properly
+// legalized and don't create type mismatches in generated CUDA code.
+
+#define ZOMBIE_PROBLEM_DIMENSION 3
+
+public interface IExample<let DIM : int>
+{
+    // computes the distance to the boundary
+    float compute(vector<float, DIM> x);
+};
+
+public struct Query<Example,let DIM : int>
+    where Example : IExample<DIM>
+{
+    // private AbsorbingBoundaryGeometricQueries absorbingBoundaryGeometricQueries;
+    private Example query;
+    private uint hasNonEmptyAbsorbingBoundary;
+
+    public float compute(vector<float, DIM> x)
+    {
+        return query.compute(x);
+    }
+};
+
+public struct EmptyExample<let DIM : int> : IExample<DIM>
+{
+    // computes the distance to the boundary
+    public float compute(vector<float, DIM> x)
+    {
+        internal static const float FLT_MAX = 3.402823466e+38F;
+        return FLT_MAX;
+    }
+};
+
+
+typedef EmptyExample<ZOMBIE_PROBLEM_DIMENSION> ExampleQuery;
+typedef Query<ExampleQuery, ZOMBIE_PROBLEM_DIMENSION> QueryType;
+
+
+uniform ParameterBlock<QueryType> gQuery;
+uniform RWStructuredBuffer<float3> gInput;
+uniform RWStructuredBuffer<float> gOutput;
+
+
+[shader("compute")]
+[numthreads(256, 1, 1)]
+void runPointEstimator(uint3 threadId: SV_DispatchThreadID,
+                       uniform uint n)
+{
+    const uint idx = threadId.x;
+
+    if (idx >= n) {
+        return;
+    }
+
+    float res = gQuery.compute(gInput[idx]);
+    gOutput[idx] = res;
+}
+
+// CHECK-NOT: Query_1