[llvm] [DirectX] Propagate shader flags mask of callees to callers (PR #118306)

[S. Bharadwaj Yadavalli via llvm-commits]

bharadwajy wrote:

> > > A few more comments on the algorithm. Also we should probably have a test that has an SCC of size greater than one.
> > 
> > 
> > Call Graph of code in `propagate-function-flags-test.ll` has an SCC with size 3. Let me know if you had some other test scenario in mind. Thanks!
> 
> Ah, that's true, but it doesn't seem to be a very good test case. Consider:
> 
> ```diff
> diff --git a/llvm/lib/Target/DirectX/DXILShaderFlags.cpp b/llvm/lib/Target/DirectX/DXILShaderFlags.cpp
> index 0392d3c84735..01bf300a7f02 100644
> --- a/llvm/lib/Target/DirectX/DXILShaderFlags.cpp
> +++ b/llvm/lib/Target/DirectX/DXILShaderFlags.cpp
> @@ -97,19 +97,12 @@ void ModuleShaderFlags::initialize(Module &M) {
>        // Update combined shader flags mask for all functions in this SCC
>        SCCSF.merge(CSF);
> 
> -      CurSCCFuncs.push_back(F);
> +      FunctionFlags[F].merge(SCCSF);
>      }
> 
>      // Update combined shader flags mask for all functions of the module
>      CombinedSFMask.merge(SCCSF);
> 
> -    // Shader flags mask of each of the functions in an SCC of the call graph is
> -    // the union of all functions in the SCC. Update shader flags masks of
> -    // functions in CurSCC accordingly. This is trivially true if SCC contains
> -    // one function.
> -    for (Function *F : CurSCCFuncs)
> -      // Merge SCCSF with that of F
> -      FunctionFlags[F].merge(SCCSF);
>    }
>  }
> ```
> 
> With this, `propagate-function-flags-test.ll` still passes (perhaps by coincidence). So it doesn't seem to be a very good test of how we're handling SCCs with more than one function.

Expanded `propagate-function-flags.ll` to test the case highlighted above.

https://github.com/llvm/llvm-project/pull/118306