Add basic reflection query for checking if entry point is "sample-rate"

- This really just checks two basic things:
  1. Was there any global variable declared with `in` and `sample`?
  2. Did any code encountered during lowering referenece `gl_SampleIndex`?

- This doesn't cover what HLSL could need, nor what we would need for cross-compilation. Consider it GLSL-specific for now.

- In order to generate the information with even a reasonable chance of being accurate (not giving a ton of false positives) I tried to integrate the checks into the lowering process (so they only see code that is referenced, one hopes).
  - For this to work with my testing setup, I needed to make sure that lowering is always performed, prior to emitting reflection info
  - This change broke several reflection tests, because they had been using code that wouldn't actually pass the downstream compiler. I checked in fixes for those.

1 files changed, 17 insertions, 0 deletions

diff --git a/source/slang/reflection.cpp b/source/slang/reflection.cpp
index 8e5044d13..1beacc21b 100644
--- a/source/slang/reflection.cpp
+++ b/source/slang/reflection.cpp
@@ -751,6 +751,18 @@ SLANG_API void spReflectionEntryPoint_getComputeThreadGroupSize(
     }
 }
 
+SLANG_API int spReflectionEntryPoint_usesAnySampleRateInput(
+    SlangReflectionEntryPoint* inEntryPoint)
+{
+    auto entryPointLayout = convert(inEntryPoint);
+    if(!entryPointLayout)
+        return 0;
+
+    if (entryPointLayout->profile.GetStage() != Stage::Fragment)
+        return 0;
+
+    return (entryPointLayout->flags & EntryPointLayout::Flag::usesAnySampleRateInput) != 0;
+}
 
 // Shader Reflection
 
@@ -1497,6 +1509,11 @@ static void emitReflectionEntryPointJSON(
         write(writer, "\n]");
     }
 
+    if (entryPoint->usesAnySampleRateInput())
+    {
+        write(writer, ",\n\"usesAnySampleRateInput\": true");
+    }
+
     dedent(writer);
     write(writer, "\n}");
 }