Generalize collectInductionValues (#3031)

* Generalize collectInductionValues

* Support affine transformations of loop index as induction variables

* Test for generalized induction value collection

* Neaten inductive variable finding

* Store the type of implication success when finding inductive variables

* Test that loop induction finding does not alway succeed

* Support chains of additions and branches of additions in induction variable finding

* Use c++17 for downstream compilers

1 files changed, 43 insertions, 0 deletions

diff --git a/tests/autodiff/long-while-loop.slang b/tests/autodiff/long-while-loop.slang
new file mode 100644
index 000000000..20d802e2a
--- /dev/null
+++ b/tests/autodiff/long-while-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:SIMPLE(filecheck=CHECK): -target hlsl -profile cs_5_0 -entry computeMain -line-directive-mode none
+
+//TEST_INPUT:ubuffer(data=[0], stride=4):out,name=outputBuffer
+RWStructuredBuffer<float> outputBuffer;
+
+[BackwardDifferentiable]
+float sin_series(float x, int iterations)
+{
+    float result = x;
+    float term = x;
+    int i = 1;
+    [MaxIters(30)]
+    do
+    {
+        term *= -1.0f * x * x / ((2 * i) * (2 * i + 1));
+        result += term;
+        i++;
+    } while (i < iterations);
+    return result;
+}
+
+// Check that the intermediate context of sin_series does not have an array for `i`.
+// This differs from ./long-loop.slang in that it uses an equivalent do/while
+// loop, this tests checks that induction variables are still correctly identified.
+
+// CHECK: struct s_bwd_sin_series_Intermediates
+// CHECK-NOT: int {{[A-Za-z0-9_]+}}[{{.*}}]
+// CHECK: }
+
+[numthreads(1, 1, 1)]
+void computeMain(uint3 dispatchThreadID: SV_DispatchThreadID)
+{
+    var x = diffPair(float.getPi(), 1.0);
+
+    __bwd_diff(sin_series)(x, 30, 1.0f);
+
+    outputBuffer[0] = x.d; // -1.0
+}
+
+
+