no_diff diagnostics improvement (#7655)

close #6286.

This PR is to improve the diagnostics for no_diff usage.

In a differentiable function, any calls to a non-diff function with constant arguments should not require no_diff attribute.
This PR adds this extra check at `checkAutoDiffUsages` where it checks the differentiability on IR.

In a differentiable method, we will force to use `[NoDiffThis]` attribute if there is access to non-differentiable `This` type. Once this access is detected we will report a warning to bring users attention that this access won't generate any derivative, they have to use `[NoDiffThis]` to suppress that warning.
This PR adds this check at type checking stage, because it's the easiest way to find out all the `This` accesses.

1 files changed, 1 insertions, 0 deletions

diff --git a/tests/autodiff/material2/DiffuseMaterial.slang b/tests/autodiff/material2/DiffuseMaterial.slang
index 1422ee30c..a5c0aaa30 100644
--- a/tests/autodiff/material2/DiffuseMaterial.slang
+++ b/tests/autodiff/material2/DiffuseMaterial.slang
@@ -16,6 +16,7 @@ public struct DiffuseMaterial : IMaterial
     }
 
     [BackwardDifferentiable]
+    [NoDiffThis]
     public DiffuseMaterialInstance setupMaterialInstance(out MaterialInstanceData miData)
     {
         float3 albedo = getAlbedo(baseColor);