Added `[BackwardDifferentiable]` tags for intrinsic + builtin methods (#2732)

* Added higher-order differentiability decorators for built-ins + preliminary tests

* Update diff.meta.slang

4 files changed, 104 insertions, 0 deletions

diff --git a/tests/autodiff/high-order-builtins-1.slang b/tests/autodiff/high-order-builtins-1.slang
new file mode 100644
index 000000000..6b0c33ca6
--- /dev/null
+++ b/tests/autodiff/high-order-builtins-1.slang
@@ -0,0 +1,47 @@
+//TEST(compute):COMPARE_COMPUTE_EX:-cpu -compute -output-using-type -shaderobj
+//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 0 0 0], stride=4):out,name=outputBuffer
+RWStructuredBuffer<float> outputBuffer;
+
+[BackwardDifferentiable]
+float f(float x)
+{
+    return x * x;
+}
+
+[BackwardDifferentiable]
+float outerF(float x)
+{
+    return f(sin(x));
+}
+
+[BackwardDifferentiable]
+float df(float x)
+{
+    return __fwd_diff(outerF)(DifferentialPair<float>(x, 1.0)).d; // 4*sin^3(x)
+}
+
+[numthreads(1, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    // Given f(x) = sin^2(x),
+    // f'(x) = 2*sin(x)*cos(x)
+    // f''(x) = 2*cos^2(x) - 2*sin^2(x)
+    //
+
+    // Expect f''(4) = -0.291
+    {
+        var p = diffPair(4.0, 0.0);
+        __bwd_diff(df)(p, 1.0);
+        outputBuffer[0] = p.d;
+    }
+
+    // Expect f''(4) = -0.653643
+    {
+        var p = diffPair(2.0, 0.0);
+        __bwd_diff(df)(p, 0.5);
+        outputBuffer[1] = p.d;
+    }
+}
diff --git a/tests/autodiff/high-order-builtins-1.slang.expected.txt b/tests/autodiff/high-order-builtins-1.slang.expected.txt
new file mode 100644
index 000000000..4fa4ade6d
--- /dev/null
+++ b/tests/autodiff/high-order-builtins-1.slang.expected.txt
@@ -0,0 +1,5 @@
+type: float
+-0.291000
+-0.653643
+0.000000
+0.000000
diff --git a/tests/autodiff/high-order-builtins-2.slang b/tests/autodiff/high-order-builtins-2.slang
new file mode 100644
index 000000000..b15dee7c7
--- /dev/null
+++ b/tests/autodiff/high-order-builtins-2.slang
@@ -0,0 +1,47 @@
+//TEST(compute):COMPARE_COMPUTE_EX:-cpu -compute -output-using-type -shaderobj
+//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 0 0 0], stride=4):out,name=outputBuffer
+RWStructuredBuffer<float> outputBuffer;
+
+[BackwardDifferentiable]
+float f(float x)
+{
+    return sin(x) + x * x;
+}
+
+[BackwardDifferentiable]
+float outerF(float x)
+{
+    return f(pow(x, 3));
+}
+
+[BackwardDifferentiable]
+float df(float x)
+{
+    return __fwd_diff(outerF)(DifferentialPair<float>(x, 1.0)).d; // x^3 + x^6
+}
+
+[numthreads(1, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    // Given f(x) = sin(x^3) + x^6
+    // f'(x) = cos(x^3)*(3*x^2) + 6*x^5
+    // f''(x) = 6*cos(x^3)*x - 9*sin(x^3)*(x^4) + 30*x^4
+    //
+
+    // Expect f''(4) = -0.291
+    {
+        var p = diffPair(1.0, 0.0);
+        __bwd_diff(df)(p, 1.0);
+        outputBuffer[0] = p.d;
+    }
+
+    // Expect f''(4) = -0.653643
+    {
+        var p = diffPair(2.0, 0.0);
+        __bwd_diff(df)(p, 0.5);
+        outputBuffer[1] = p.d;
+    }
+}
diff --git a/tests/autodiff/high-order-builtins-2.slang.expected.txt b/tests/autodiff/high-order-builtins-2.slang.expected.txt
new file mode 100644
index 000000000..9f5d74b29
--- /dev/null
+++ b/tests/autodiff/high-order-builtins-2.slang.expected.txt
@@ -0,0 +1,5 @@
+type: float
+25.668574
+167.893206
+0.000000
+0.000000