More fixes for reverse-mode on complicated loops (#2675)

* Multiple fixes to get various loop tests to pass.

* Create reverse-nested-loop.slang

* Fix for variables becoming inaccessible during cfg normalization

* Removed comments and moved break-branch-normalization to eliminateMultiLevelBreaks

* Fix.

* Override liveness tests

1 files changed, 43 insertions, 0 deletions

diff --git a/tests/autodiff/reverse-nested-loop.slang b/tests/autodiff/reverse-nested-loop.slang
new file mode 100644
index 000000000..08cde5230
--- /dev/null
+++ b/tests/autodiff/reverse-nested-loop.slang
@@ -0,0 +1,43 @@
+//TEST(compute):COMPARE_COMPUTE_EX:-slang -compute -shaderobj -output-using-type
+//TEST(compute, vulkan):COMPARE_COMPUTE_EX:-vk -compute -shaderobj -output-using-type
+//TEST(compute):COMPARE_COMPUTE_EX:-cpu -compute -output-using-type -shaderobj
+
+//TEST_INPUT:ubuffer(data=[0 0 0 0 0], stride=4):out,name=outputBuffer
+RWStructuredBuffer<float> outputBuffer;
+
+typedef DifferentialPair<float> dpfloat;
+typedef float.Differential dfloat;
+
+[BackwardDifferentiable]
+float test_simple_nested_loop(float y)
+{
+    float t = y;
+
+    for (int i = 0; i < 2; i++)
+    {
+        for (int j = 0; j < 2; j++)
+        {
+            t = t * (i + j + 1);
+        }
+    }
+    
+    return t;
+}
+
+[numthreads(1, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    {
+        dpfloat dpa = dpfloat(1.0, 0.0);
+
+        __bwd_diff(test_simple_nested_loop)(dpa, 1.0f);
+        outputBuffer[0] = dpa.d; // Expect: 12.0 * 1
+    }
+
+    {
+        dpfloat dpa = dpfloat(1.0, 0.0);
+
+        __bwd_diff(test_simple_nested_loop)(dpa, 0.4f);
+        outputBuffer[1] = dpa.d; // Expect: 12 * 0.4 = 4.8
+    }
+}