Fix type checking & loop value hoisting (#2907)

* Fix type checking crash in language server.

* Fix loop var hoisting logic.

Fixes #2903.

* fix.

---------

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

2 files changed, 80 insertions, 0 deletions

diff --git a/tests/autodiff/reverse-loop-diff-only-3.slang b/tests/autodiff/reverse-loop-diff-only-3.slang
new file mode 100644
index 000000000..e36b6c09c
--- /dev/null
+++ b/tests/autodiff/reverse-loop-diff-only-3.slang
@@ -0,0 +1,74 @@
+//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;
+
+// Test that compute does not have a context.
+// CHECK-NOT: struct {{[a-zA-Z0-9_]*}}_compute_{{[a-zA-Z0-9_]*}}
+
+[BackwardDifferentiable]
+[PreferRecompute]
+float compute(float x, float y, out float k)
+{
+    k = y * 2;
+    return x * y;
+}
+
+// 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;
+    int i = 0;
+    [MaxIters(8)]
+    do
+    {
+        float k = float(0.f);
+        w += compute(i, y, k);
+        w += k * k;
+        i++;
+    }
+    while (i < 8);
+
+    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-3.slang.expected.txt b/tests/autodiff/reverse-loop-diff-only-3.slang.expected.txt
new file mode 100644
index 000000000..fedac0520
--- /dev/null
+++ b/tests/autodiff/reverse-loop-diff-only-3.slang.expected.txt
@@ -0,0 +1,6 @@
+type: float
+93.000000
+27.300001
+0.000000
+0.000000
+0.000000