Fix bug in legalizeFuncType that leads to invalid IR. (#2902)

* Fix bug in legalizeFuncType that leads to invalid IR.

* Diagnose on functions that never returns when differentiate it.

---------

Co-authored-by: Yong He <yhe@nvidia.com>

1 files changed, 43 insertions, 0 deletions

diff --git a/tests/diagnostics/unbound-loop.slang b/tests/diagnostics/unbound-loop.slang
new file mode 100644
index 000000000..5e85c3c66
--- /dev/null
+++ b/tests/diagnostics/unbound-loop.slang
@@ -0,0 +1,43 @@
+//TEST:SIMPLE(filecheck=CHECK): -entry computeMain -target hlsl -profile cs_6_5
+
+
+RWStructuredBuffer<float> outputBuffer;
+
+typedef DifferentialPair<float> dpfloat;
+typedef float.Differential dfloat;
+
+// CHECK: function 'test_loop_with_continue' never returns
+[BackwardDifferentiable]
+float test_loop_with_continue(float y)
+{
+    float t = y;
+    
+    // OOPS! No `++i`! 
+    for (int i = 0; i < 3;)
+    {
+        if (t > 4.0)
+            continue;
+
+        t = t * t;
+    }
+
+    return t;
+}
+
+[numthreads(1, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    {
+        dpfloat dpa = dpfloat(2.0, 0.0);
+
+        __bwd_diff(test_loop_with_continue)(dpa, 1.0f);
+        outputBuffer[0] = dpa.d; // Expect: 32.0
+    }
+
+    {
+        dpfloat dpa = dpfloat(0.4, 0.0);
+
+        __bwd_diff(test_loop_with_continue)(dpa, 1.0f);
+        outputBuffer[1] = dpa.d; // Expect: 0.0131072
+    }
+}
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