Add a loop analysis step to infer the exit values of loop phi parameters. (#6696)

* Initial loop analysis pass

* More changes for a single-pass implication propagation

* Update slang-ir-autodiff-loop-analysis.cpp

* Cleanup + new system for loop analysis

* Fixup bugs in loop analysis

* Remove some relation types to simplify the analysis. Add test

* Remove unused

* Address comments

* Fix issue with continue loops

* Update reverse-loop-exit-value-inference-1.slang

* Update reverse-continue-loop.slang

1 files changed, 46 insertions, 0 deletions

diff --git a/tests/autodiff/reverse-loop-simple.slang b/tests/autodiff/reverse-loop-simple.slang
new file mode 100644
index 000000000..18b672860
--- /dev/null
+++ b/tests/autodiff/reverse-loop-simple.slang
@@ -0,0 +1,46 @@
+//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
+//DISABLE_TEST:SIMPLE(filecheck=CHK):-target glsl -stage compute -entry computeMain -report-checkpoint-intermediates
+
+//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;
+
+//CHK: note: checkpointing context of 24 bytes associated with function: 'test_simple_loop'
+[Differentiable]
+float test_simple_loop(float y)
+{
+    //CHK: note: 20 bytes (FixedArray<float, 5> ) used to checkpoint the following item:
+    float t = y;
+
+    //CHK: note: 4 bytes (int32_t) used for a loop counter here:
+    for (int i = 0; i < 3; i++)
+    {
+        t = t * t;
+    }
+
+    return t;
+}
+
+[numthreads(1, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    {
+        dpfloat dpa = dpfloat(1.0, 0.0);
+
+        __bwd_diff(test_simple_loop)(dpa, 1.0f);
+        outputBuffer[0] = dpa.d; // Expect: 8.0
+    }
+
+    {
+        dpfloat dpa = dpfloat(0.4, 0.0);
+
+        __bwd_diff(test_simple_loop)(dpa, 1.0f);
+        outputBuffer[1] = dpa.d; // Expect: 0.0131072
+    }
+}
+
+//CHK-NOT: note
\ No newline at end of file