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, 4 insertions, 0 deletions

diff --git a/tests/autodiff/dynamic-object-bwd-diff.slang b/tests/autodiff/dynamic-object-bwd-diff.slang
index a10c48f9b..a80025d52 100644
--- a/tests/autodiff/dynamic-object-bwd-diff.slang
+++ b/tests/autodiff/dynamic-object-bwd-diff.slang
@@ -26,7 +26,9 @@ struct C : IInterface2
 struct A : IInterface
 {
     float a;
+
     [BackwardDifferentiable]
+    [NoDiffThis]
     float calc(IInterface2 i2, float x)
     {
         float b = no_diff(i2.innerCalc(x));
@@ -37,7 +39,9 @@ struct A : IInterface
 struct B : IInterface
 {
     float a;
+
     [BackwardDifferentiable]
+    [NoDiffThis]
     float calc(IInterface2 i2, float x)
     {
         float b = no_diff(i2.innerCalc(x));