Update checkpoint policy to make obvious recompute decisions. (#2753)

* Update checkpoint policy to make obvious recompute decisions.

Also adds an optimization to fold updateElement chains on the same array or struct into a single makeArray or makeStruct.

* Bug fixes around array types with different int typed count.

* change test.

* Fix.

---------

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

2 files changed, 85 insertions, 0 deletions

diff --git a/tests/autodiff/array-param.slang b/tests/autodiff/array-param.slang
new file mode 100644
index 000000000..fd78b3246
--- /dev/null
+++ b/tests/autodiff/array-param.slang
@@ -0,0 +1,83 @@
+
+//TEST(compute):COMPARE_COMPUTE_EX:-slang -compute -shaderobj -output-using-type
+//TEST(compute, vulkan):COMPARE_COMPUTE_EX:-vk -compute -shaderobj -output-using-type
+
+//TEST_INPUT:ubuffer(data=[0], stride=4):out,name=outputBuffer
+RWStructuredBuffer<float> outputBuffer;
+
+static const uint32_t N_LATENT_DIMS = 4;
+static const uint32_t kDecoderInputCount = 6;
+struct LatentTexture
+{
+    static const uint32_t kLatentDimsCount = N_LATENT_DIMS;
+    static const uint32_t kLatentTextureCount = N_LATENT_DIMS / 4;
+
+    [BackwardDifferentiable]
+    void getCodeStochastic(float2 uv, out float code[kLatentDimsCount])
+    {
+        return getCode(uint2(1,2), code);
+    }
+
+    void getCode(uint2 texel, out float code[kLatentDimsCount])
+    {
+        for (uint i = 0; i < kLatentTextureCount; ++i)
+        {
+            for (uint j = 0; j < 4; ++j)
+            {
+                code[i * 4 + j] = j;
+            }
+        }
+    }
+    [BackwardDerivativeOf(getCode)]
+    void bwd_getCode(uint2 texel, float d_out[kLatentDimsCount])
+    {
+        outputBuffer[0] = d_out[0];
+    }
+}
+
+static LatentTexture gLatents;
+
+[BackwardDifferentiable]
+void test(float arr[10], out float result[3])
+{
+    float sum = 0;
+    [ForceUnroll]
+    for (int i = 0; i < LatentTexture.kLatentDimsCount + kDecoderInputCount; i++)
+        sum += arr[i];
+    result[0] = sum;
+    result[1] = sum;
+    result[2] = sum;
+}
+
+[BackwardDifferentiable]
+float evalDecoder()
+{
+    // Latent code.
+    float latentCode[LatentTexture.kLatentDimsCount];
+    gLatents.getCodeStochastic(float2(1,2), latentCode);
+
+    // Model input.
+    float input[kDecoderInputCount + LatentTexture.kLatentDimsCount];
+    input[0] = 0;
+    input[1] = 1;
+    input[2] = 2;
+    input[3] = 3;
+    input[4] = 4;
+    input[5] = 5;
+    [ForceUnroll]
+    for (int i = 0; i < LatentTexture.kLatentDimsCount; i++)
+    {
+        input[kDecoderInputCount + i] = latentCode[i];
+    }
+
+    float res[3];
+    test(input, res);
+    return res[0] + res[1] + res[2];
+}
+
+
+[numthreads(1, 1, 1)]
+void computeMain(uint3 dispatchThreadID: SV_DispatchThreadID)
+{
+    __bwd_diff(evalDecoder)(1.0);
+}
diff --git a/tests/autodiff/array-param.slang.expected.txt b/tests/autodiff/array-param.slang.expected.txt
new file mode 100644
index 000000000..f38cc1080
--- /dev/null
+++ b/tests/autodiff/array-param.slang.expected.txt
@@ -0,0 +1,2 @@
+type: float
+3.0