Fix handling of `[PreferRecompute]`. (#2855)

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

2 files changed, 78 insertions, 0 deletions

diff --git a/tests/autodiff/reverse-loop-diff-only.slang b/tests/autodiff/reverse-loop-diff-only.slang
new file mode 100644
index 000000000..64db4b814
--- /dev/null
+++ b/tests/autodiff/reverse-loop-diff-only.slang
@@ -0,0 +1,72 @@
+//TEST(compute):COMPARE_COMPUTE_EX:-slang -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 0 0 0 0], stride=4):out,name=outputBuffer
+RWStructuredBuffer<float> outputBuffer;
+
+typedef DifferentialPair<float> dpfloat;
+typedef float.Differential dfloat;
+
+[BackwardDifferentiable]
+[PreferRecompute]
+float compute(float x, float y)
+{
+    return x * y;
+}
+
+[BackwardDifferentiable]
+[ForceInline]
+float infinitesimal(float x)
+{
+    return x - detach(x);
+}
+
+// Test that computeLoop compiles to just return 0.
+// CHECK: float computeLoop{{[_0-9]*}}(float y{{[_0-9]*}})
+// CHECK-NOT: for{{.*}}
+// CHECK: return 0
+
+[BackwardDifferentiable]
+[PreferRecompute]
+float computeLoop(float y)
+{
+    float w = 0;
+
+    for (int i = 0; i < 8; i++)
+    {
+        w += compute(i, y);
+    }
+
+    return w - detach(w);
+}
+
+// Since computeLoop is recomputed, test_simple_loop should have nothing to store
+// therefore we check that there is no intermediate context type generated for test_simple_loop.
+
+// CHECK-NOT: struct {{[a-zA-Z0-9_]*}}test_simple_loop{{[a-zA-Z0-9_]*}}
+[BackwardDifferentiable]
+float test_simple_loop(float y)
+{  
+    float x = computeLoop(y);
+    return y + x;
+}
+
+[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: 29.0
+    }
+
+    {
+        dpfloat dpa = dpfloat(0.4, 0.0);
+
+        __bwd_diff(test_simple_loop)(dpa, 0.5f);
+        outputBuffer[1] = dpa.d; // Expect: 14.5
+    }
+
+    outputBuffer[2] = computeLoop(1.0);
+}
diff --git a/tests/autodiff/reverse-loop-diff-only.slang.expected.txt b/tests/autodiff/reverse-loop-diff-only.slang.expected.txt
new file mode 100644
index 000000000..f3b93a6a8
--- /dev/null
+++ b/tests/autodiff/reverse-loop-diff-only.slang.expected.txt
@@ -0,0 +1,6 @@
+type: float
+29.000000
+14.500000
+0.000000
+0.000000
+0.000000